TV Color question

Discussion in 'Archived Threads 2001-2004' started by Thomas B, Jun 23, 2001.

  1. Thomas B

    Thomas B Agent

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    I asked this question a few days ago over on the TV section of the forum, but didn't get a response, so I am trying again over here. This may be so basic that it is embarrassing for me not to know this, but nevertheless, here goes . . .
    Can someone explain to me the terms "color bias","color temperature" and "color aperture improvement", and the significance of these controls? Thanks.
     
  2. Jay Mitchosky

    Jay Mitchosky Producer

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    quote: Can someone explain to me the terms "color bias","color temperature" and "color aperture improvement", and the significance of these controls?[/quote]
    Wow. I've never heard of "bias" or "aperture improvement". They're probably different terms for something very basic. But I can explain color temperature...
    Every color image you see on a TV is a function of black and white image below. That's where it starts. The shade or tint of the underlying grayscale is referred to as color temperature. It is defined as the temperature you would have to heat a theoretical black body until it becomes gray. In our system of television the standard temperature is 6500 degrees Kelvin, which is somewhat the color of a uniformly overcast sky in the middle of the day. Less than 6500 degrees the gray takes on a reddish tint, above it begins to get blue.
    If the grayscale is tinted than the overall image will be as well, regardless of how you set your Color and Tint controls. Most consumer sets are calibrated to varying extremes above 6500K - manufacturers do this to compete on the showroom floor as our eyes perceive bluer as brighter and whiter. TVs can be recalibrated to achieve the correct grayscale, but a professional with proper measurement equipment is required. The resulting image is more natural with a greater degree of snap (the colors tend to leap out more, and blacks are deeper).
    On your TV you are able to select different (factory set) color temperatures, usually labelled Warm, Medium, and Cool. This refers to the underlying grayscale. Warm will appear relatively red compared to Cool, which is very blue. On most sets Warm is closest to 6500K but is still generally well above. The Cool settings can easily double the reference standard 6500K. Strangely these labels are misnomers. The blue end of the scale is actually hotter in terms of degrees Kelvin than the red end. But I guess people tend to associate red/warm and blue/cool more than the other way around.
    Do a search for posts by Allan Jayne and follow his signature link to his site for video definitions galore. You can also refer to Errol's HDTV website and the Imaging Science Foundation.
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    --Jay
    "No one can hear when you're screaming in digital."
    My Home Theatre Pictures...
    "You're no mesiah. You're, you're a movie of the week. You're a ... t-shirt, at best."
     
  3. Thomas B

    Thomas B Agent

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    Jay, thanks so much for your answer! I have been busy and away for awhile and have just now been able to respond. I have an old (circa 1993) Mitsubishi 35-inch direct view set, CS-35FX1. I realize this set is quite outdated now, but it still has a great picture and I am trying to delay purchase of another set until later when HDTV sets are more reasonable and the standards are settled.
    Anyway, the video control labeled "color bias" on this set has three options from which to choose: Average, Skin-tone, and Accurate. Can you explain what is involved for each of these settings?
    The control labeled "CAI" indicates what the manual calls "Color Aperture Improvement". This is an on/off control, and apparently is a type of noise reduction for color (but is separate from the actual Video Noise Reduction control.) I haven't really seen much difference in the picture whether this control is on or off.
    Also, one additional question on the color temperature control . . . your explanation was fine, but my TV shows three options for Color Temp: High, Middle, and Low. Is it correct to assume that "High" implies "cool", "Middle" implies "medium" (DUH!) and "Low" implies "warm"?
    Thanks again!
     
  4. Jay Mitchosky

    Jay Mitchosky Producer

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    Hey Thomas
    Welcome back! [​IMG] To try and answer your other questions...
     
  5. Thomas B

    Thomas B Agent

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    Thanks again, Jay. As for the "color bias" feature, there is no "OFF" option, so I viewed various scenes on DVD and settled on "Accurate" as the best level for this setting. On normal TV viewing, the "Average" setting appears better in some instances.
    As you suggested, I am leaving that "CAI" control on "OFF" since I really can't discern any difference with this.
    Now, back to the color temperature . . . I examined the various black and white video test patterns on the Avia DVD, and yes, it is very obvious that the "High" color setting is blue and the "Low" is more reddish. The "Middle" setting does appear to be a more neutral gray shade, as you predicted. You mentioned that I should stick with the more red setting. However, does this correspond with the "red push" effect? Avia mentions that this should be minimized as much as possible. Would setting my color temp at "Low" make this "red push" effect worse? Thanks again!
     
  6. Jay Mitchosky

    Jay Mitchosky Producer

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    quote: . You mentioned that I should stick with the more red setting.[/quote]
    Hey Thomas
    Seems you and I have our own private forum running here. [​IMG] You don't want to stick with the "more red" setting, but rather the one that produces the most neutral gray. In comparison to the High setting then, yes, it will definitely appear more red. But the goal is a neutral shade of gray. Most monitors tend be closest in the Warm (or Low in your case) setting, but there are others where Medium/Middle is best. Somebody in another thread offered an intriguing idea to acclimating your eyes to a neutral gray: stare at a black and white newspaper outside mid-day with a uniformly overcast sky. Use that as your reference and judge accordingly. Given that the High setting is definitely out spend some time watching Avia's gray fields (use 70IRE) in Low mode. Walk away and give your eyes a break. Come back and do the same thing in Middle mode. How does the color of gray look? Does it look more or less gray compared to the Low mode? Is it tinted a particular color? Stick with the setting that strikes you as the most neutral.
    quote: ...does this correspond with the "red push" effect? Would setting my color temp at "Low" make this "red push" effect worse?[/quote]
    Primarily not - grayscale and color saturation are separate entities. However, an overly red grayscale would exaggerate an extreme red push. A neutral grayscale would still have a red push (it's the decoder's fault), while the other colors would be fine. To use a "bluer" grayscale to de-emphasize the red oversaturation would serve to wash out the non-red colors in the spectrum.
    Find the most accurate color temperature setting first (limited of course by the available factory settings). Then deal with your red push (post calibration) by backing off on the Color control. Don't touch Tint once calibrated. You will find blue/green undersaturation less objectionable than red oversaturation - that's just the way our eyes work.
    Now, with that in mind...
    Until recently Mitsubishi sets had a very unique capability. In service mode you were able to individually set color and tint for EACH element of the color decoder (ie. RGB). You could use the red color bars and red filter from Avia and adjust red saturation/tint. Same for green bars/filter/sat/tint, and same again for blue. Imagine doing the blue filter thing but for green and red as well. Result? Perfect saturation and tint for all three colors and 0% push/pull. I'm not sure if that ability applied to their direct views, or if it was included in the 1993 model year. Their 2001 sets no longer allow this degree of adjustment, which is really too bad (considering Mits is one of the biggest red push offenders). Search here, Errol's HDTV, and Home Theater Spot for instructions on how to enter service mode and whether or not your set will allow this.
    ------------------
    --Jay
    "No one can hear when you're screaming in digital."
    My Home Theatre Pictures...
    "You're no mesiah. You're, you're a movie of the week. You're a ... t-shirt, at best."
     

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