ChrisWiggles
Senior HTF Member
- Joined
- Aug 19, 2002
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Background Guide to Setting Source Options
Why am I writing this guide?
Simple! There has been a great deal of confusion about the settings and ‘calibrations’ of source devices. Well-intentioned users commonly misunderstand the functions of some adjustments, and end up unintentionally degrading their image quality. This FAQ /guide is an attempt to filter through some of the mess and assemble a decent background in one place, so that you can do your best to make sure that your playback chain is not degrading your video unnecessarily.
The layout:
I’ve organized this guide into two parts with background sections first, in the hope that everyone will want to read the background first before going on to adjust settings and calibrate. For you throw-away-the-manual adventurers, you can skip ahead to the adjustment section that applies to your system. The numbers match between the two parts, so if you’ve skipped ahead to the goodies of finding the right setting and it’s confusing, circling back to the background explanation may help!
Say, who’s behind this fiasco of a FAQ? What’s the conspiracy!
I’ve written and compiled this material with the help of Guy Kuo, Keith Jack, Stacey Spears, Joe Murphy Jr, Bob Pariseau, and the indirect help of many other knowledgeable folks, posts, books, alternate personalities etc. Thanks guys! Much of this background has already been discussed on the forums, but is scattered and obscured by popular misinformation. My hope is to unite a solid background that is sorely lacking.
Wait a minute, you’re wrong about _____!
I’ve taken great care to make sure the information is trustworthy by having some of the biggest video super-heroes check to make sure the content is solid, so you might actually find that if you read through the background you’ll discover that what you read in the past may not have been as correct as you thought. But if I have left something out or made a mistake, let me know and I’ll fix it! I have used some simplified terms, for instance I label non-linear R’G’B’ simply RGB, etc, for simplicity and clarity: this is not likely to cause any confusion since I can’t fathom any HT environment dealing in any non-corrected linear RGB values!
What tools do I need?
If you are a Home Theater enthusiast, I should certainly hope you already own a copy of Avia or Digital Video Essentials. If you’re a nut like me you own both, and perhaps also Avia PRO! For testing Studio versus PC levels Avia PRO or DVE are necessary.
BACKGROUND
1)Analog input/outputs from digital sources
Say, what the heck is an IRE?
As often as the term IRE is thrown around when discussing video, relatively few actually know what it means!
An IRE simply a representation of volts: there are with 140 IRE units in one volt. This simplified expressing the ~700mV excursion of an analog video waveform, with white represented using 100 IRE instead of an odd 714mV. As I will describe, IRE units are ambiguous at describing the intended image content unless you know whether or not the 7.5 IRE setup pedestal is present. Many do not grasp that IRE is merely another way to represent volts, and as such confuse IRE into some mysterious value that magically describes the actual image information, which cannot do without caveats.
North American NTSC standards historically used a level for the analog output of black that was 53.6mV (aka 7.5 IRE) above the blanking voltage of 0mV (0 IRE), and we still do. Other standards like HD, Japanese NTSC, etc use 0mV to output black, and lack the 53.6mV (7.5 IRE) ‘setup pedestal’ that North America uses. This IRE setup option allows you to switch between these two voltage output levels for black. Neither will necessarily provide any universal increase in picture quality: it merely alters the voltage output that is used to represent black. With a correctly designed player and a good display, upon recalibrating your display to the new source outputs, your picture would be identical. As we all know the ideal player is rare and displays vary, so in some systems one setting may be preferred over the other to prevent a degraded picture. But neither setting is universally preferred. I’ve explained how to examine the behavior of your specific system to determine which setting(if any) is preferred in the second half of this FAQ.
Test patterns from test DVDs are (unfortunately, in my opinion) often labeled or described in IRE units. These are merely labels, and they usually assume the presence of setup, thus the source outputs black at 7.5 IRE. If there is no setup then the source is outputting black at 0IRE and the labels on the test patterns are now wrong for that system. The absolute IRE levels will change depending on the behavior of the source device, and the DVD has no control over this. These charts accurately show that the encoded digital values that are the stimulus do not change, while the absolute mV outputs (hence IRE values) will change depending on the voltage for black output:
**
For Avia and Avia PRO--
7.5 IRE output:
0 IRE output:
“Players with a 0 IRE representation for black and 100 IRE for 100% white will output IRE levels that don't match the on disc labeling would do the following. Notice that the relationship between labeled IRE and percent stimulus remains the same as for players with 7.5 IRE setup. However, the output IRE and mV change.” -GK
**
(From Guy Kuo)
You can see that in a system that outputs black at 7.5IRE, the labels are accurate. In a system that outputs black at 0IRE, the labels must be recalculated: actual IRE levels when setup is not present = (labeled IRE-7.5) * 100/92.5. You can see that an Avia pattern labeled 10 IRE will end up about being output at a voltage about 2.5IRE (more accurately 2.7 IRE or 19.29mV) in a system without setup. As long as the display is correctly calibrated to the source, the pattern should be imaged correctly.
If that last portion seemed like too many numbers, don’t worry! The most important point you need to take away is that IRE units are merely another way of expressing mV.
It should be obvious already that DVDs are not analog. They contain digitally encoded video. As such, there are no voltages read from a DVD(it’s an optical media!). By extension, there are of course no absolute IRE units represented on a DVD. A DVD uses 8-bit digital levels from 1-254 to represent the image data. Only when that data must be output in an analog form do voltages, hence IRE, even come into play. That’s right: if you are using a digital output, there is no analog video signal, thus IRE units do not come into play in any form (cautious note: the adjustment may unintentionally affect digital output, but if designed correctly it should not.).
Because many have confused IRE units into some mysterious creature of a unit, they’ve confused digital levels and IRE as somehow being the same: i.e. that IRE are encoded on DVDs, or that DVDs only go down to 7.5 IRE while HD has better black capabilities because HD goes down to 0 IRE.
This is rubbish.
Both HD material and DVDs use the same digital levels. It is the ANALOG output standards which can vary. The encoded levels represent black just as black. The dynamic range is the same. Video encodes black at digital 16. Period. That’s black, and whether it is output at 0 IRE or 7.5 IRE the resultant image should be equally black. If there is any difference in the visible levels of black, your video chain is miscalibrated. If you connect sources that output at various voltages, you have to calibrate to EACH of these sources. Users will often connect a DVD player that outputs black at 7.5 IRE, then connect an HD source that outputs black at 0 IRE, discover that the HD source is darker, and mistakenly conclude that HD has improved black capabilities. This discovery of changed blacks is merely that you have different sources sending different signals. You must calibrate your display to each individually.
If you’ve followed this far, then you’ll see that the following types of statements(some repeated often) are complete nonsense:
WRONG! Blacker-than-black data has nothing to do with whether a source outputs at 0 IRE or 7.5 IRE. You know already that IRE is just mV, and absolute mV are not encoded in any way on the DVD. The DVD is encoded in digital values from 1-254. Reference black is encoded at digital 16, with nominal reference white at 235. Codes 0 and 255 are illegal for image data. Codes 1-15 represent data that is below reference black, hence it is called blacker-than-black (BTB). Codes 236-254 are peak whites. I will refrain from calling them ‘whiter than white’ because this implies that they shouldn’t normally be present or visible in the final picture. They should be, unlike BTB(BTB should not regularly be visible in the final calibrated image)! It is important to maintain the full range of encoded data through your video chain for the best image. When the digital image data is converted into an analog waveform at an analog output, only then does IRE enter the picture. BTB data will simply fall below whatever the IRE output level for black is. In a system that outputs black at 7.5 IRE, BTB data will be output at voltages slightly below 7.5 IRE. In a system that outputs black at 0 IRE, BTB data will be output at voltages slightly below 0mV (simply negative volts). If you’ve digested that correctly, you realize that BTB data can be maintained in BOTH situations.
Unfortunately, in reality DVD players are often designed poorly and may clip BTB data. Some will clip BTB in both settings, others will clip it in one or the other. A correctly designed DVD player will maintain BTB data at analog output regardless of whether it is set to output black at 0 IRE or 7.5 IRE.
“Why does data below black even exist? That makes no sense! What can be blacker than black!?”
In video, headroom and footroom is important for a number of reasons. The most basic is that mastering can be less than perfect, so some “fudge-room” has always existed. However, even with ‘perfect’ mastering, data regularly extends outside reference black/reference white. Peak white data allows for highlight details to be maintained, which is common in clouds and other bright objects. BTB data helps prevent image anomalies from hard clipping of the analog waveform at black when converted to analog. BTB can also sometimes become visible as the actual black level on a CRT display floats up and down with image content because black level retention on CRTs is not perfect. The mastering engineer is viewing on a CRT display and actively changing the encoded levels so that they are imaged correctly on the display. This reverse-float compensation in black is allowed with BTB footroom. This reverse float compensation should be the only times data encoded below black is visible in the final image. If you are using a PLUGE pattern with BTB bars to calibrate, you should calibrate so that the BTB data is not visible. BTB data also helps define dithering duty patterns on DLP projectors. Lastly, BTB and peak white data is quite useful for any image processing/scaling etc applied to an image. For all these potential reasons, video engineers advocate preserving full BTB and peak white data whenever possible. Lastly, this data is helpful for any image processing that is applied on an image, such as sharpening, scaling, etc.
Now you should understand better what an IRE is, what the 7.5 IRE/0 IRE difference does NOT entail, and what blacker-than-black data really is.
For more reading, see posts in these threads:
http://www.avsforum.com/avs-vb/showt...61#post4030461
http://archive2.avsforum.com/avs-vb/...09#post3307309
This thread has some useful attached pictures that label patterns with their actual encoded values in digital levels, and not in ambiguous IRE units. The digital levels written to the disc itself are fixed and absolute even though the analog voltages vary. Knowing the digital values tells you exactly what a portion of the pattern should look like. Parts encoded 16 are unambiguously black, always!:
http://www.avsforum.com/avs-vb/showt...hreadid=418084
2) Digital outputs and digital levels
I explained IRE in background section 1, so you should already recognize that IRE only describes analog waveforms, and is ambiguous as to the actual intended image content. When using digital transmission formats like SDI, DVI, HDMI, analog measurements like IRE units or mV are useless for describing the image data. As briefly explained before, digital video uses 8-bit encoding, which creates 256 unique steps from 0-255.
Video from DVDs or other digital sources, follows Studio RGB standards which encodes reference black at level 16, and nominal reference white at level 235. Outside these bounds is the footroom and headroom that contain blacker-than-black(BTB) and peak white data. Footroom and headroom is necessary for the best possible video reproduction for the reasons discussed briefly in background section 1:
Mastering fudge room
Highlight details and undershoot
Minimizing analog waveform anomalies at D/A converters
Compensation for the inability of CRTs to clamp black levels perfectly
Determining dithering patterns on DLPs
Any image processing applied
Enter the PC.
If you’re a computer graphics person, you may recognize the 0-255 scale of digital levels. But you may be confused because with computer graphics black is at 0, white is at 255, and that’s it! There is no footroom or headroom for BTB or peak white data. Since computers and video often have to be dealt with at the same time, this creates a problem between PC levels and Studio levels.
Projectors with digital inputs have to be able to handle both video applications and computer graphics applications. They should be able to calibrate or switch their white and black levels to accommodate both Studio levels and PC levels, but some don’t. Because video sources and graphics sources may be used simultaneously in some applications, video source manufacturers tend to include an option to leave the digital outputs at Studio levels, or to re-map them to PC levels.
Mapping Studio levels to PC levels can be done a few ways. Sometimes all the levels are just shifted down 16 steps, thus clipping off BTB data, but not introducing banding/contouring or clipping highlight details. If there are other PC level sources fed to the display, their whites will be substantially brighter. The clipping of BTB data is undesirable and the brightness mis-match is also noticeable, however note that there will be no banding problems. Usually the levels are expanded: digital 16 (black) is shifted down to 0, and 235 (white) is shifted up to 255 (or sometimes a value slightly lower than 255) thus expanding the numerical range between black and white to match PC levels. Note that this doesn’t improve contrast in the final image. In this case, re-mapping Studio levels to PC levels will destroy BTB and peak white image data, and introduce banding/contouring artifacts because of the expansion. This is also undesirable.
Always try to maintain Studio levels whenever possible in your system. You should use Avia PRO or DVE to test whether or not levels are being clipped. Both discs contain patterns with both BTB and peak white data. Note that the current consumer Avia does not, it only contains data in the range or 16-235. Thus if BTB or peak white data is being clipped, you won’t see it with Avia! If you are clipping the black or white bars in Avia, then your system is doing even more severe damage to the video by clipping above black shadow details and below-white detail: very bad! Note that Avia PRO also has some very useful ramp patterns with levels encoded at equal width so as to be completely banding-free. These are very useful for observing banding/contouring caused by the playback system.
For more reading, see this thread, especially the expert posts by Don Munsil and Stacey Spears:
http://www.avsforum.com/avs-vb/showt...hreadid=416292
3) Upconverting players and possible colorspace issues
This issue is still a fairly obscure one, and at this point I am including it only for the sake of being comprehensive. My concern is that people will read this portion about colorspace problems, and blame all color problems on this issue when it may have nothing to do with what they are seeing.
Note that this specific discussion ONLY applies to component video outputs: analog YPbPr or digital HDMI YCbCr.
This issue may arise in other narrow situations, but is quite unlikely.
(I’ve labeled ITU-R Recommendations BT.601 and BT.709 simply SD 601 and HD 709 so readers can follow which is which as they read)
If you are using YPbPr/YCbCr output, you are outputting component video that is actually encoded on the DVD. Your display is then transforming this component video into a form that it can use to drive the display (usually always RGB). The problem that can arise is that Standard Definition material uses one set of equations (SD 601) to move between RGB and YPbPr/YCbCr, while High Definition material uses a slightly different equation (HD709). A DVD is a digital SD source, as such the YCbCr on it was created using the SD 601 equations and should be decoded into RGB using the same SD 601 matrix or color errors will result.
Your display will likely apply either the SD 601 or the HD 709 decoding depending on the resolution it is seeing at input. An upconverting DVD player is sending an HD signal that your TV will respond to by decoding using the HD 709 decoding(usually). Unfortunately, your upconverting DVD player may or may not have properly re-coded the component video into HD 709. If it did not, then you have a mismatch: SD 601 encoded material is being incorrectly decoded with HD 709 equations. This color encode/decode mismatch will lead to color errors.
Note again that this section is included for the sake of being comprehensive. The actual source material is unpredictable, and may or may not be encoded using the proper color matrix. In my opinion, it is worthwhile for enthusiasts and video purists to consider and fix this colorspace problem if present, but because the problem is fairly limited to mis-designed upscaling DVD players at this point, I don’t see it as a concern for the majority of users. Hopefully, manufacturers will design upconverting players correctly to twist the color space into HD 709 before output.
See especially Stacey’s images attached in post 2 of this thread, along with the discussions nearing the end of the thread:
http://www.avsforum.com/avs-vb/showt...0&pagenumber=1
4) HTPCs
Because HTPCs are a huge discussion area, I can’t hope to cover all the possible problems that can arise with all the software, drivers, hardware, settings, etc that can come into play. In any case, I just reiterate that it is important to design your HTPC and settings purposefully so that you can maintain Studio RGB for video playback, and calibrate your display to this and not to the graphics’ PC RGB levels.
See the Computers and HTPC forum here at HTF!
******** ON TO THE SETTINGS! ********
1) For DVD players when using Analog outputs (Composite, S-video, Component video):
When using analog outputs, many DVD players have an option to change the IRE ouput level for black between 7.5 IRE and 0 IRE. There have been many misleading posts suggesting that 0 IRE output universally provides “deeper” blacks, is necessary to maintain blacker-than-black data, increases the picture’s contrast, or otherwise will improve your picture. These recommendations are not correct. To understand why, read the explanations in background #1 that differentiate between analog output voltage levels represented by IRE, and the actual digitally encoded values on the DVD.
Q: “So which IRE output setting should I use, and since it varies between players and systems how do I know what’s right for my system?”
A: There are two main performance considerations to take into account:
a) First is the adjustment range of your display. The most important thing to do is to make sure that your display has enough black level adjustment range(brightness) to accommodate either 0 IRE or 7.5 IRE output for black. Most displays should have plenty of adjustment range to handle both, but if you find that no matter how far you raise or lower your black level setting that your black levels remain either submerged (too dark) or elevated (too bright: grayish) with one of the output settings, make sure you use the other setting that allows the combination of your DVD player’s output and your display’s adjustment range to show black properly. If you find yourself in this situation, keep this setting, and do not continue on to the other considerations, as proper black level in the image is the most important. In most cases, though, you will find that your display will have enough adjustment range to handle both output voltages properly. If both are handled properly, then the next thing to consider in choosing between 0 IRE and 7.5 IRE is blacker-than-black (BTB) data:
b) Next to consider is the preservation of blacker-than-black data. This issue has been confused a lot, so if my recommendations don’t agree with what you’ve been told in the past, please read the explanations behind them (background #1).
Ideally, a DVD player will preserve the full range of digital data contained on a DVD when outputting an analog signal in both the 0IRE setting, and the 7.5 IRE setting. In practice, many times this is not the case. To find out whether a specific player will pass blacker-than-black data, and in which setting, it must be tested. Reviewers sometimes describe whether or not a player passes BTB data, but unless the settings and connection method for this test are revealed, the information is not very useful. Some players will correctly pass BTB data in both settings, while many others will only pass BTB data in one of the settings, and some will clip BTB data in BOTH settings. (Others will perform still worse and clip more than just BTB data, but also clip above-black shadow details; hopefully you do not have a player like this!) To test for BTB data, you must use a test disc that contains such data, namely Avia PRO, or DVE. Note that consumer Avia does not contain BTB data. If you are clipping the black bars in Avia, your system is clipping even more than just BTB data: it is clipping above-black shadow details as well. Using the PLUGE patterns on DVE is the most likely scenario for the average enthusiast, but if you do have access to Avia Pro I recommend using it.
Using DVE, I particularly like Title 12, Chps 13-15. Chp 13 has a 20% center bar that is not blindingly bright when you raise your black levels to see the three bars beside it. If you’re not familiar with DVE, the two pairs of inner bars are above black, the background is black (digital 16) and the outermost pair of bars are below black. If your system is preserving BTB data, you will see all three bars when you raise your black level at your display to observe. If BTB data is being clipped, you will only see the inner two pairs of bars: the outermost below-black bars will appear black and match the background, which is black. Chp 14 is a useful full-range ramp marked by dots at the points for reference white and black. Chp 15 has a ramp in the lower portion of the pattern that runs from slightly above black to below black. Black crosses at the center.
After you’ve tested your DVD player to see whether it passes BTB, and in which setting(s), you should choose one that maintains BTB data. Note again that this is secondary to being able to calibrate black in your system properly in the first step. I hope users will share their player-specific findings on the preservation of BTB data in both of these settings to aid others who have the same player!
If you have a well-designed player that passes BTB data in BOTH the 0IRE and 7.5IRE output modes, then you can use either one. Always note that you have to calibrate to your chosen setting. If you do not recalibrate, your picture will be wrong: the black level output on your DVD player will not match the display’s calibration which leads to elevated or submerged blacks in the final image.
Extra: The last consideration is only if you have a player that correctly passes BTB data in both settings AND your display can be calibrated properly to either output: convenience. If you have enough inputs on your display, and per-input calibration adjustments, then you can go ahead and calibrate each input to a particular source, and it won’t matter which setting you choose. However, many times multiple sources are run through switchers, receivers, etc, or there are no per-input calibrations on your display. If you have sources conforming to different IRE standards, you would need to recalibrate your display each time you switched between them. This is annoying! You may want to set your DVD player to match the other sources more closely, which should eliminate the need to recalibrate between sources. While sources always will vary slightly in analog outputs and it is ideal to have individual calibrations for each source, when using a switcher, etc, this is often not possible. In my opinion, these slight differences are a worthy sacrifice for convenience, as few will want to recalibrate between different sources at 7.5 and 0IRE each time, and not recalibrating in this situation will result in very incorrect black levels and a significantly degraded picture for the odd source that is using a different output level. Where possible, always calibrate for each individual source, as voltage output precision isn’t always perfect! Where not possible, using the same output standards can be an acceptable compromise instead of needing to recalibrate the display each time you switch sources. How acceptable a compromise this is depends on how accurately the sources hit the standard voltages. If they vary widely enough as to be objectionable with a single calibration, you may just need to live with adjusting your display calibrations frequently.
2) For DVD players when using a digital output (DVI, HDMI).
When using digital outputs, your primary concern is to get the DVD’s image data output as undisturbed as possible. As simple as this might seem, design/price constraints, sloppy engineering, and ‘features’ can get in the way of transferring the digital data from the DVD intact. Always try to avoid using any image-altering features such as picture controls. These adjustments will usually have negative impacts on picture quality.
When using digital outputs, the major adjustment option you have is the one for digital levels. As is common in consumer labeling, the labels for this can be confusing. The most common labeling will at least hopefully show that you are making an adjustment to the DVI/HDMI digital outputs, and usually the options will read ‘Normal/Enhanced’ or ‘Normal/Expanded’ or ‘Video/PC,’ or some such label. The latter is clearer, as this adjustment is choosing whether or not the digital image data is correctly output using Studio (also called Video) levels, or is incorrectly re-mapped to PC levels. You should choose to maintain Studio levels by checking to make sure this option is properly set. Usually the default setting will correctly choose the option for Studio levels. Check to make sure.
Note that the Studio/PC level option will only work for DVI and HDMI RGB. If you are using HDMI YCbCr, Studio levels should be preserved correctly(and as far as I’m aware sources aren’t screwing this up, yet…) and the option change will either have no effect or be unavailable.
Because you are using digital outputs, adjustments for analog outputs shouldn’t be a consideration. Unfortunately again, due to cost-saving designs sometimes analog output adjustments, such as those for IRE setup, are implemented digitally even though they have nothing to do with digital outputs. Here your concern is still to ensure that the digital image data is being left as undisturbed as possible. In a well-designed player, the IRE option will have no effect whatsoever when using digital outputs. If this setting causes any change in the image when using the digital outputs, you should use test patterns to see which option leaves data un-clipped. In this instance, the degree of clipping or image alterations may be severe, so Avia, DVE, or any good test disc will come in handy. In Avia, look for the moving near-black and near-white white bars; in DVE use the ramps (Title12:Chp14) and check for clipping (if you have access to Avia PRO, the Deep Ramps are excellent tests!). Use the IRE setup setting that maintains as much data as possible through to your display. The default setting may more likely be the preferred setting. Default is usually the 7.5IRE setting. This was reported to be the case on the Denon 3910; users should test this on their players and share model-specific observations to aid others!
With the hope that digital levels and IRE are conceptually disentangled, you should understand that the IRE setup option is really for the analog output, and shouldn’t have to be discussed when using digital outputs. Unfortunately, instead of implementing these analog adjustments in the analog domain, cost-conscious designs seem to be altering the digital values, which necessitates double-checking this option to make sure your digital levels are not being tampered with.
3) Colorspace issues with upconverting DVD players
This is written only for those who are using component video, either analog YPbPr or digital HDMI YCbCr output. If you are using analog RGB, DVI(which is digital RGB)or HDMI RGB output this section does not apply to you! I omitted composite and s-video because of course you cannot output HD video via either.
A DVD is a digital SD source, as such the YCbCr on it was created using the SD 601 equations and should be decoded using the same matrix or color errors will result. Upconverting players should be modifying the colorspace to match the HD 709 coding, but some do not. Most displays will simply apply SD 601 decoding to any SD inputs, and HD 709 decoding to any HD inputs. If an upconverting player left the SD 601 colorspace encode intact, a display that applies HD 709 decoding to any HD inputs will unknowingly apply the wrong decode, leading to color errors. I place the blame with the DVD player.
You can check for this color problem by examining the color decoder test pattern on Avia(found under the section Special Tests: Color Decoder Check). If the player is upconverting to an HD resolution and not twisting the colorspace into 709, you will likely see color decoding errors in the Avia test pattern, with the most significant one being green depression(note that this is not a grayscale error but a color decoding error, and will not depend on you having correct grayscale: you will see this problem on the color decoder check pattern regardless!). To avoid these color decoding errors, your display may allow you to change between 709 and 601 manually. If it does not, using HDMI RGB or DVI RGB (analog RGB is a rarity, but also would avoid this problem) should eliminate this problem. If your only output option is analog component video YPbPr and your display does not have its own upscaling capabilities, then you may have to live with these color errors.
4) HTPCs
If you are using an HTPC, I will dodge the complex arena that is computer video, and merely recommend strongly that you do your best to maintain Studio levels and prevent your computer from expanding the video to PC levels. To check this, examine deep ramps on Avia PRO, or use the ramps and PLUGE patterns on DVE. Note that consumer Avia does not contain data outside the bounds of reference black/white (16-235) so you will not be able to observe the clipping of data outside these bounds using Avia. Moving to PC levels will usually clip data 1-15 and 235-255(or significant portions of this data); this data is present in the ramps and PLUGE patterns on DVE and in many patterns on Avia PRO.
Remember that proper playback of video requires Studio levels to maintain the full range of image data. This includes data outside the ‘bounds’ of the reference black/white points. Achieving this on a PC can be difficult sometimes, and it also means that your desktop and your video cannot both look correct at the same time. Expanding your video to match PC levels (0-255) will make your desktop and your video ‘agree’ and eliminate the need to recalibrate, but you’ve also negatively impacted video playback by clipping useful image data and introducing banding/contouring artifacts. This is undesirable, you should strive to maintain Studio levels if at all possible. Since this guide is directed at HT enthusiasts, I am assuming that accurate video playback is priority #1. I acknowledge that for users in other environments(multi-use, graphics etc) the problems introduced by expanding to PC levels might be an acceptable compromise for convenience. But wherever you strive for the best possible video quality, Studio levels are fundamental.
CZ
**I considered not including the links to AVS posts as it is an outside forum, however the particular expert posts there are superb. I think this guide functions well without them, but I'd like to include them for the time being for those who would like a little more reading. If it is an issue, I can remove them.
Thanks!
--Chris
Why am I writing this guide?
Simple! There has been a great deal of confusion about the settings and ‘calibrations’ of source devices. Well-intentioned users commonly misunderstand the functions of some adjustments, and end up unintentionally degrading their image quality. This FAQ /guide is an attempt to filter through some of the mess and assemble a decent background in one place, so that you can do your best to make sure that your playback chain is not degrading your video unnecessarily.
The layout:
I’ve organized this guide into two parts with background sections first, in the hope that everyone will want to read the background first before going on to adjust settings and calibrate. For you throw-away-the-manual adventurers, you can skip ahead to the adjustment section that applies to your system. The numbers match between the two parts, so if you’ve skipped ahead to the goodies of finding the right setting and it’s confusing, circling back to the background explanation may help!
Say, who’s behind this fiasco of a FAQ? What’s the conspiracy!
I’ve written and compiled this material with the help of Guy Kuo, Keith Jack, Stacey Spears, Joe Murphy Jr, Bob Pariseau, and the indirect help of many other knowledgeable folks, posts, books, alternate personalities etc. Thanks guys! Much of this background has already been discussed on the forums, but is scattered and obscured by popular misinformation. My hope is to unite a solid background that is sorely lacking.
Wait a minute, you’re wrong about _____!
I’ve taken great care to make sure the information is trustworthy by having some of the biggest video super-heroes check to make sure the content is solid, so you might actually find that if you read through the background you’ll discover that what you read in the past may not have been as correct as you thought. But if I have left something out or made a mistake, let me know and I’ll fix it! I have used some simplified terms, for instance I label non-linear R’G’B’ simply RGB, etc, for simplicity and clarity: this is not likely to cause any confusion since I can’t fathom any HT environment dealing in any non-corrected linear RGB values!
What tools do I need?
If you are a Home Theater enthusiast, I should certainly hope you already own a copy of Avia or Digital Video Essentials. If you’re a nut like me you own both, and perhaps also Avia PRO! For testing Studio versus PC levels Avia PRO or DVE are necessary.
BACKGROUND
1)Analog input/outputs from digital sources
Say, what the heck is an IRE?
As often as the term IRE is thrown around when discussing video, relatively few actually know what it means!
An IRE simply a representation of volts: there are with 140 IRE units in one volt. This simplified expressing the ~700mV excursion of an analog video waveform, with white represented using 100 IRE instead of an odd 714mV. As I will describe, IRE units are ambiguous at describing the intended image content unless you know whether or not the 7.5 IRE setup pedestal is present. Many do not grasp that IRE is merely another way to represent volts, and as such confuse IRE into some mysterious value that magically describes the actual image information, which cannot do without caveats.
North American NTSC standards historically used a level for the analog output of black that was 53.6mV (aka 7.5 IRE) above the blanking voltage of 0mV (0 IRE), and we still do. Other standards like HD, Japanese NTSC, etc use 0mV to output black, and lack the 53.6mV (7.5 IRE) ‘setup pedestal’ that North America uses. This IRE setup option allows you to switch between these two voltage output levels for black. Neither will necessarily provide any universal increase in picture quality: it merely alters the voltage output that is used to represent black. With a correctly designed player and a good display, upon recalibrating your display to the new source outputs, your picture would be identical. As we all know the ideal player is rare and displays vary, so in some systems one setting may be preferred over the other to prevent a degraded picture. But neither setting is universally preferred. I’ve explained how to examine the behavior of your specific system to determine which setting(if any) is preferred in the second half of this FAQ.
Test patterns from test DVDs are (unfortunately, in my opinion) often labeled or described in IRE units. These are merely labels, and they usually assume the presence of setup, thus the source outputs black at 7.5 IRE. If there is no setup then the source is outputting black at 0IRE and the labels on the test patterns are now wrong for that system. The absolute IRE levels will change depending on the behavior of the source device, and the DVD has no control over this. These charts accurately show that the encoded digital values that are the stimulus do not change, while the absolute mV outputs (hence IRE values) will change depending on the voltage for black output:
**
For Avia and Avia PRO--
7.5 IRE output:
Code:
LabeledPercentOutputOutput
IREStimIREmV
7.50.07.553.6
102.710.071.4
2013.520.0142.9
3024.330.0214.3
4035.140.0285.7
5045.950.0357.1
6056.860.0428.6
7067.670.0500.0
8078.480.0571.4
9089.290.0642.9
100100.0100.0714.30 IRE output:
“Players with a 0 IRE representation for black and 100 IRE for 100% white will output IRE levels that don't match the on disc labeling would do the following. Notice that the relationship between labeled IRE and percent stimulus remains the same as for players with 7.5 IRE setup. However, the output IRE and mV change.” -GK
Code:
LabeledPercentOutputOutput
IREStimIREmV
7.50.00.00.0
102.72.719.3
2013.513.596.5
3024.324.3173.7
4035.135.1251.0
5045.945.9328.2
6056.856.8405.4
7067.667.6482.6
8078.478.4559.8
9089.289.2637.1
100100.0100.0714.3**
(From Guy Kuo)
You can see that in a system that outputs black at 7.5IRE, the labels are accurate. In a system that outputs black at 0IRE, the labels must be recalculated: actual IRE levels when setup is not present = (labeled IRE-7.5) * 100/92.5. You can see that an Avia pattern labeled 10 IRE will end up about being output at a voltage about 2.5IRE (more accurately 2.7 IRE or 19.29mV) in a system without setup. As long as the display is correctly calibrated to the source, the pattern should be imaged correctly.
If that last portion seemed like too many numbers, don’t worry! The most important point you need to take away is that IRE units are merely another way of expressing mV.
It should be obvious already that DVDs are not analog. They contain digitally encoded video. As such, there are no voltages read from a DVD(it’s an optical media!). By extension, there are of course no absolute IRE units represented on a DVD. A DVD uses 8-bit digital levels from 1-254 to represent the image data. Only when that data must be output in an analog form do voltages, hence IRE, even come into play. That’s right: if you are using a digital output, there is no analog video signal, thus IRE units do not come into play in any form (cautious note: the adjustment may unintentionally affect digital output, but if designed correctly it should not.).
Because many have confused IRE units into some mysterious creature of a unit, they’ve confused digital levels and IRE as somehow being the same: i.e. that IRE are encoded on DVDs, or that DVDs only go down to 7.5 IRE while HD has better black capabilities because HD goes down to 0 IRE.
This is rubbish.
Both HD material and DVDs use the same digital levels. It is the ANALOG output standards which can vary. The encoded levels represent black just as black. The dynamic range is the same. Video encodes black at digital 16. Period. That’s black, and whether it is output at 0 IRE or 7.5 IRE the resultant image should be equally black. If there is any difference in the visible levels of black, your video chain is miscalibrated. If you connect sources that output at various voltages, you have to calibrate to EACH of these sources. Users will often connect a DVD player that outputs black at 7.5 IRE, then connect an HD source that outputs black at 0 IRE, discover that the HD source is darker, and mistakenly conclude that HD has improved black capabilities. This discovery of changed blacks is merely that you have different sources sending different signals. You must calibrate your display to each individually.
If you’ve followed this far, then you’ll see that the following types of statements(some repeated often) are complete nonsense:
WRONG! Blacker-than-black data has nothing to do with whether a source outputs at 0 IRE or 7.5 IRE. You know already that IRE is just mV, and absolute mV are not encoded in any way on the DVD. The DVD is encoded in digital values from 1-254. Reference black is encoded at digital 16, with nominal reference white at 235. Codes 0 and 255 are illegal for image data. Codes 1-15 represent data that is below reference black, hence it is called blacker-than-black (BTB). Codes 236-254 are peak whites. I will refrain from calling them ‘whiter than white’ because this implies that they shouldn’t normally be present or visible in the final picture. They should be, unlike BTB(BTB should not regularly be visible in the final calibrated image)! It is important to maintain the full range of encoded data through your video chain for the best image. When the digital image data is converted into an analog waveform at an analog output, only then does IRE enter the picture. BTB data will simply fall below whatever the IRE output level for black is. In a system that outputs black at 7.5 IRE, BTB data will be output at voltages slightly below 7.5 IRE. In a system that outputs black at 0 IRE, BTB data will be output at voltages slightly below 0mV (simply negative volts). If you’ve digested that correctly, you realize that BTB data can be maintained in BOTH situations.
Unfortunately, in reality DVD players are often designed poorly and may clip BTB data. Some will clip BTB in both settings, others will clip it in one or the other. A correctly designed DVD player will maintain BTB data at analog output regardless of whether it is set to output black at 0 IRE or 7.5 IRE.
“Why does data below black even exist? That makes no sense! What can be blacker than black!?”
In video, headroom and footroom is important for a number of reasons. The most basic is that mastering can be less than perfect, so some “fudge-room” has always existed. However, even with ‘perfect’ mastering, data regularly extends outside reference black/reference white. Peak white data allows for highlight details to be maintained, which is common in clouds and other bright objects. BTB data helps prevent image anomalies from hard clipping of the analog waveform at black when converted to analog. BTB can also sometimes become visible as the actual black level on a CRT display floats up and down with image content because black level retention on CRTs is not perfect. The mastering engineer is viewing on a CRT display and actively changing the encoded levels so that they are imaged correctly on the display. This reverse-float compensation in black is allowed with BTB footroom. This reverse float compensation should be the only times data encoded below black is visible in the final image. If you are using a PLUGE pattern with BTB bars to calibrate, you should calibrate so that the BTB data is not visible. BTB data also helps define dithering duty patterns on DLP projectors. Lastly, BTB and peak white data is quite useful for any image processing/scaling etc applied to an image. For all these potential reasons, video engineers advocate preserving full BTB and peak white data whenever possible. Lastly, this data is helpful for any image processing that is applied on an image, such as sharpening, scaling, etc.
Now you should understand better what an IRE is, what the 7.5 IRE/0 IRE difference does NOT entail, and what blacker-than-black data really is.
For more reading, see posts in these threads:
http://www.avsforum.com/avs-vb/showt...61#post4030461
http://archive2.avsforum.com/avs-vb/...09#post3307309
This thread has some useful attached pictures that label patterns with their actual encoded values in digital levels, and not in ambiguous IRE units. The digital levels written to the disc itself are fixed and absolute even though the analog voltages vary. Knowing the digital values tells you exactly what a portion of the pattern should look like. Parts encoded 16 are unambiguously black, always!:
http://www.avsforum.com/avs-vb/showt...hreadid=418084
2) Digital outputs and digital levels
I explained IRE in background section 1, so you should already recognize that IRE only describes analog waveforms, and is ambiguous as to the actual intended image content. When using digital transmission formats like SDI, DVI, HDMI, analog measurements like IRE units or mV are useless for describing the image data. As briefly explained before, digital video uses 8-bit encoding, which creates 256 unique steps from 0-255.
Video from DVDs or other digital sources, follows Studio RGB standards which encodes reference black at level 16, and nominal reference white at level 235. Outside these bounds is the footroom and headroom that contain blacker-than-black(BTB) and peak white data. Footroom and headroom is necessary for the best possible video reproduction for the reasons discussed briefly in background section 1:
Mastering fudge room
Highlight details and undershoot
Minimizing analog waveform anomalies at D/A converters
Compensation for the inability of CRTs to clamp black levels perfectly
Determining dithering patterns on DLPs
Any image processing applied
Enter the PC.
If you’re a computer graphics person, you may recognize the 0-255 scale of digital levels. But you may be confused because with computer graphics black is at 0, white is at 255, and that’s it! There is no footroom or headroom for BTB or peak white data. Since computers and video often have to be dealt with at the same time, this creates a problem between PC levels and Studio levels.
Projectors with digital inputs have to be able to handle both video applications and computer graphics applications. They should be able to calibrate or switch their white and black levels to accommodate both Studio levels and PC levels, but some don’t. Because video sources and graphics sources may be used simultaneously in some applications, video source manufacturers tend to include an option to leave the digital outputs at Studio levels, or to re-map them to PC levels.
Mapping Studio levels to PC levels can be done a few ways. Sometimes all the levels are just shifted down 16 steps, thus clipping off BTB data, but not introducing banding/contouring or clipping highlight details. If there are other PC level sources fed to the display, their whites will be substantially brighter. The clipping of BTB data is undesirable and the brightness mis-match is also noticeable, however note that there will be no banding problems. Usually the levels are expanded: digital 16 (black) is shifted down to 0, and 235 (white) is shifted up to 255 (or sometimes a value slightly lower than 255) thus expanding the numerical range between black and white to match PC levels. Note that this doesn’t improve contrast in the final image. In this case, re-mapping Studio levels to PC levels will destroy BTB and peak white image data, and introduce banding/contouring artifacts because of the expansion. This is also undesirable.
Always try to maintain Studio levels whenever possible in your system. You should use Avia PRO or DVE to test whether or not levels are being clipped. Both discs contain patterns with both BTB and peak white data. Note that the current consumer Avia does not, it only contains data in the range or 16-235. Thus if BTB or peak white data is being clipped, you won’t see it with Avia! If you are clipping the black or white bars in Avia, then your system is doing even more severe damage to the video by clipping above black shadow details and below-white detail: very bad! Note that Avia PRO also has some very useful ramp patterns with levels encoded at equal width so as to be completely banding-free. These are very useful for observing banding/contouring caused by the playback system.
For more reading, see this thread, especially the expert posts by Don Munsil and Stacey Spears:
http://www.avsforum.com/avs-vb/showt...hreadid=416292
3) Upconverting players and possible colorspace issues
This issue is still a fairly obscure one, and at this point I am including it only for the sake of being comprehensive. My concern is that people will read this portion about colorspace problems, and blame all color problems on this issue when it may have nothing to do with what they are seeing.
Note that this specific discussion ONLY applies to component video outputs: analog YPbPr or digital HDMI YCbCr.
This issue may arise in other narrow situations, but is quite unlikely.
(I’ve labeled ITU-R Recommendations BT.601 and BT.709 simply SD 601 and HD 709 so readers can follow which is which as they read)
If you are using YPbPr/YCbCr output, you are outputting component video that is actually encoded on the DVD. Your display is then transforming this component video into a form that it can use to drive the display (usually always RGB). The problem that can arise is that Standard Definition material uses one set of equations (SD 601) to move between RGB and YPbPr/YCbCr, while High Definition material uses a slightly different equation (HD709). A DVD is a digital SD source, as such the YCbCr on it was created using the SD 601 equations and should be decoded into RGB using the same SD 601 matrix or color errors will result.
Your display will likely apply either the SD 601 or the HD 709 decoding depending on the resolution it is seeing at input. An upconverting DVD player is sending an HD signal that your TV will respond to by decoding using the HD 709 decoding(usually). Unfortunately, your upconverting DVD player may or may not have properly re-coded the component video into HD 709. If it did not, then you have a mismatch: SD 601 encoded material is being incorrectly decoded with HD 709 equations. This color encode/decode mismatch will lead to color errors.
Note again that this section is included for the sake of being comprehensive. The actual source material is unpredictable, and may or may not be encoded using the proper color matrix. In my opinion, it is worthwhile for enthusiasts and video purists to consider and fix this colorspace problem if present, but because the problem is fairly limited to mis-designed upscaling DVD players at this point, I don’t see it as a concern for the majority of users. Hopefully, manufacturers will design upconverting players correctly to twist the color space into HD 709 before output.
See especially Stacey’s images attached in post 2 of this thread, along with the discussions nearing the end of the thread:
http://www.avsforum.com/avs-vb/showt...0&pagenumber=1
4) HTPCs
Because HTPCs are a huge discussion area, I can’t hope to cover all the possible problems that can arise with all the software, drivers, hardware, settings, etc that can come into play. In any case, I just reiterate that it is important to design your HTPC and settings purposefully so that you can maintain Studio RGB for video playback, and calibrate your display to this and not to the graphics’ PC RGB levels.
See the Computers and HTPC forum here at HTF!
******** ON TO THE SETTINGS! ********
1) For DVD players when using Analog outputs (Composite, S-video, Component video):
When using analog outputs, many DVD players have an option to change the IRE ouput level for black between 7.5 IRE and 0 IRE. There have been many misleading posts suggesting that 0 IRE output universally provides “deeper” blacks, is necessary to maintain blacker-than-black data, increases the picture’s contrast, or otherwise will improve your picture. These recommendations are not correct. To understand why, read the explanations in background #1 that differentiate between analog output voltage levels represented by IRE, and the actual digitally encoded values on the DVD.
Q: “So which IRE output setting should I use, and since it varies between players and systems how do I know what’s right for my system?”
A: There are two main performance considerations to take into account:
a) First is the adjustment range of your display. The most important thing to do is to make sure that your display has enough black level adjustment range(brightness) to accommodate either 0 IRE or 7.5 IRE output for black. Most displays should have plenty of adjustment range to handle both, but if you find that no matter how far you raise or lower your black level setting that your black levels remain either submerged (too dark) or elevated (too bright: grayish) with one of the output settings, make sure you use the other setting that allows the combination of your DVD player’s output and your display’s adjustment range to show black properly. If you find yourself in this situation, keep this setting, and do not continue on to the other considerations, as proper black level in the image is the most important. In most cases, though, you will find that your display will have enough adjustment range to handle both output voltages properly. If both are handled properly, then the next thing to consider in choosing between 0 IRE and 7.5 IRE is blacker-than-black (BTB) data:
b) Next to consider is the preservation of blacker-than-black data. This issue has been confused a lot, so if my recommendations don’t agree with what you’ve been told in the past, please read the explanations behind them (background #1).
Ideally, a DVD player will preserve the full range of digital data contained on a DVD when outputting an analog signal in both the 0IRE setting, and the 7.5 IRE setting. In practice, many times this is not the case. To find out whether a specific player will pass blacker-than-black data, and in which setting, it must be tested. Reviewers sometimes describe whether or not a player passes BTB data, but unless the settings and connection method for this test are revealed, the information is not very useful. Some players will correctly pass BTB data in both settings, while many others will only pass BTB data in one of the settings, and some will clip BTB data in BOTH settings. (Others will perform still worse and clip more than just BTB data, but also clip above-black shadow details; hopefully you do not have a player like this!) To test for BTB data, you must use a test disc that contains such data, namely Avia PRO, or DVE. Note that consumer Avia does not contain BTB data. If you are clipping the black bars in Avia, your system is clipping even more than just BTB data: it is clipping above-black shadow details as well. Using the PLUGE patterns on DVE is the most likely scenario for the average enthusiast, but if you do have access to Avia Pro I recommend using it.
Using DVE, I particularly like Title 12, Chps 13-15. Chp 13 has a 20% center bar that is not blindingly bright when you raise your black levels to see the three bars beside it. If you’re not familiar with DVE, the two pairs of inner bars are above black, the background is black (digital 16) and the outermost pair of bars are below black. If your system is preserving BTB data, you will see all three bars when you raise your black level at your display to observe. If BTB data is being clipped, you will only see the inner two pairs of bars: the outermost below-black bars will appear black and match the background, which is black. Chp 14 is a useful full-range ramp marked by dots at the points for reference white and black. Chp 15 has a ramp in the lower portion of the pattern that runs from slightly above black to below black. Black crosses at the center.
After you’ve tested your DVD player to see whether it passes BTB, and in which setting(s), you should choose one that maintains BTB data. Note again that this is secondary to being able to calibrate black in your system properly in the first step. I hope users will share their player-specific findings on the preservation of BTB data in both of these settings to aid others who have the same player!
If you have a well-designed player that passes BTB data in BOTH the 0IRE and 7.5IRE output modes, then you can use either one. Always note that you have to calibrate to your chosen setting. If you do not recalibrate, your picture will be wrong: the black level output on your DVD player will not match the display’s calibration which leads to elevated or submerged blacks in the final image.
Extra: The last consideration is only if you have a player that correctly passes BTB data in both settings AND your display can be calibrated properly to either output: convenience. If you have enough inputs on your display, and per-input calibration adjustments, then you can go ahead and calibrate each input to a particular source, and it won’t matter which setting you choose. However, many times multiple sources are run through switchers, receivers, etc, or there are no per-input calibrations on your display. If you have sources conforming to different IRE standards, you would need to recalibrate your display each time you switched between them. This is annoying! You may want to set your DVD player to match the other sources more closely, which should eliminate the need to recalibrate between sources. While sources always will vary slightly in analog outputs and it is ideal to have individual calibrations for each source, when using a switcher, etc, this is often not possible. In my opinion, these slight differences are a worthy sacrifice for convenience, as few will want to recalibrate between different sources at 7.5 and 0IRE each time, and not recalibrating in this situation will result in very incorrect black levels and a significantly degraded picture for the odd source that is using a different output level. Where possible, always calibrate for each individual source, as voltage output precision isn’t always perfect! Where not possible, using the same output standards can be an acceptable compromise instead of needing to recalibrate the display each time you switch sources. How acceptable a compromise this is depends on how accurately the sources hit the standard voltages. If they vary widely enough as to be objectionable with a single calibration, you may just need to live with adjusting your display calibrations frequently.
2) For DVD players when using a digital output (DVI, HDMI).
When using digital outputs, your primary concern is to get the DVD’s image data output as undisturbed as possible. As simple as this might seem, design/price constraints, sloppy engineering, and ‘features’ can get in the way of transferring the digital data from the DVD intact. Always try to avoid using any image-altering features such as picture controls. These adjustments will usually have negative impacts on picture quality.
When using digital outputs, the major adjustment option you have is the one for digital levels. As is common in consumer labeling, the labels for this can be confusing. The most common labeling will at least hopefully show that you are making an adjustment to the DVI/HDMI digital outputs, and usually the options will read ‘Normal/Enhanced’ or ‘Normal/Expanded’ or ‘Video/PC,’ or some such label. The latter is clearer, as this adjustment is choosing whether or not the digital image data is correctly output using Studio (also called Video) levels, or is incorrectly re-mapped to PC levels. You should choose to maintain Studio levels by checking to make sure this option is properly set. Usually the default setting will correctly choose the option for Studio levels. Check to make sure.
Note that the Studio/PC level option will only work for DVI and HDMI RGB. If you are using HDMI YCbCr, Studio levels should be preserved correctly(and as far as I’m aware sources aren’t screwing this up, yet…) and the option change will either have no effect or be unavailable.
Because you are using digital outputs, adjustments for analog outputs shouldn’t be a consideration. Unfortunately again, due to cost-saving designs sometimes analog output adjustments, such as those for IRE setup, are implemented digitally even though they have nothing to do with digital outputs. Here your concern is still to ensure that the digital image data is being left as undisturbed as possible. In a well-designed player, the IRE option will have no effect whatsoever when using digital outputs. If this setting causes any change in the image when using the digital outputs, you should use test patterns to see which option leaves data un-clipped. In this instance, the degree of clipping or image alterations may be severe, so Avia, DVE, or any good test disc will come in handy. In Avia, look for the moving near-black and near-white white bars; in DVE use the ramps (Title12:Chp14) and check for clipping (if you have access to Avia PRO, the Deep Ramps are excellent tests!). Use the IRE setup setting that maintains as much data as possible through to your display. The default setting may more likely be the preferred setting. Default is usually the 7.5IRE setting. This was reported to be the case on the Denon 3910; users should test this on their players and share model-specific observations to aid others!
With the hope that digital levels and IRE are conceptually disentangled, you should understand that the IRE setup option is really for the analog output, and shouldn’t have to be discussed when using digital outputs. Unfortunately, instead of implementing these analog adjustments in the analog domain, cost-conscious designs seem to be altering the digital values, which necessitates double-checking this option to make sure your digital levels are not being tampered with.
3) Colorspace issues with upconverting DVD players
This is written only for those who are using component video, either analog YPbPr or digital HDMI YCbCr output. If you are using analog RGB, DVI(which is digital RGB)or HDMI RGB output this section does not apply to you! I omitted composite and s-video because of course you cannot output HD video via either.
A DVD is a digital SD source, as such the YCbCr on it was created using the SD 601 equations and should be decoded using the same matrix or color errors will result. Upconverting players should be modifying the colorspace to match the HD 709 coding, but some do not. Most displays will simply apply SD 601 decoding to any SD inputs, and HD 709 decoding to any HD inputs. If an upconverting player left the SD 601 colorspace encode intact, a display that applies HD 709 decoding to any HD inputs will unknowingly apply the wrong decode, leading to color errors. I place the blame with the DVD player.
You can check for this color problem by examining the color decoder test pattern on Avia(found under the section Special Tests: Color Decoder Check). If the player is upconverting to an HD resolution and not twisting the colorspace into 709, you will likely see color decoding errors in the Avia test pattern, with the most significant one being green depression(note that this is not a grayscale error but a color decoding error, and will not depend on you having correct grayscale: you will see this problem on the color decoder check pattern regardless!). To avoid these color decoding errors, your display may allow you to change between 709 and 601 manually. If it does not, using HDMI RGB or DVI RGB (analog RGB is a rarity, but also would avoid this problem) should eliminate this problem. If your only output option is analog component video YPbPr and your display does not have its own upscaling capabilities, then you may have to live with these color errors.
4) HTPCs
If you are using an HTPC, I will dodge the complex arena that is computer video, and merely recommend strongly that you do your best to maintain Studio levels and prevent your computer from expanding the video to PC levels. To check this, examine deep ramps on Avia PRO, or use the ramps and PLUGE patterns on DVE. Note that consumer Avia does not contain data outside the bounds of reference black/white (16-235) so you will not be able to observe the clipping of data outside these bounds using Avia. Moving to PC levels will usually clip data 1-15 and 235-255(or significant portions of this data); this data is present in the ramps and PLUGE patterns on DVE and in many patterns on Avia PRO.
Remember that proper playback of video requires Studio levels to maintain the full range of image data. This includes data outside the ‘bounds’ of the reference black/white points. Achieving this on a PC can be difficult sometimes, and it also means that your desktop and your video cannot both look correct at the same time. Expanding your video to match PC levels (0-255) will make your desktop and your video ‘agree’ and eliminate the need to recalibrate, but you’ve also negatively impacted video playback by clipping useful image data and introducing banding/contouring artifacts. This is undesirable, you should strive to maintain Studio levels if at all possible. Since this guide is directed at HT enthusiasts, I am assuming that accurate video playback is priority #1. I acknowledge that for users in other environments(multi-use, graphics etc) the problems introduced by expanding to PC levels might be an acceptable compromise for convenience. But wherever you strive for the best possible video quality, Studio levels are fundamental.
CZ
**I considered not including the links to AVS posts as it is an outside forum, however the particular expert posts there are superb. I think this guide functions well without them, but I'd like to include them for the time being for those who would like a little more reading. If it is an issue, I can remove them.
Thanks!
--Chris
