BryantJones

Basic Calibration w/ DVE

I just picked up DVE and my handy-dandy SPL meter. I calibrated my speakers without a hitch (minus the sub..I'm too scared to play it at 75 db ), but I'm having a problem with the basic video calibration.

How on earth do I calibrate the contrast? That 'blooming' talk made no sense whatsoever. I mean, I can see the scanlines quite clearly on my TV once I get up-close, but I don't know what to look for from there on.

Also, what do I do with the plethora of test-patterns in the reference section? There's no word on how to use them in the narration Is there a good DVE tutorial on the net?

Thanks for the help, once again!

BryantJones

Basic Calibration w/ DVE

I just picked up DVE and my handy-dandy SPL meter. I calibrated my speakers without a hitch (minus the sub..I'm too scared to play it at 75 db ), but I'm having a problem with the basic video calibration.

How on earth do I calibrate the contrast? That 'blooming' talk made no sense whatsoever. I mean, I can see the scanlines quite clearly on my TV once I get up-close, but I don't know what to look for from there on.

Also, what do I do with the plethora of test-patterns in the reference section? There's no word on how to use them in the narration Is there a good DVE tutorial on the net?

Thanks for the help, once again!

douglas-b

The short answer is..... set contrast to the LOWEST setting which still allows white to look white.

The long answer follows. This was written for AVIA but the basic principles still apply. Adjusting for just short of blooming is not the goal. Blooming is the point which should be thought as the red line for the electron guns. Just as you shouldn't keep your engine just below its red line in daily usage, you shouldn't do that with the contrast control of a CRT display. The on disc instructions for HTT and AVIA simply didn't allow time for as complete a discussion as follows. For those really wishing to do it as "right" as possible without instrumentation consider the following as superceding the on disc "instruction for the masses" on HTT, AVIA, and DVE discs....

......
Now for the more nebulous white level setting. You're quite right in noting that white level is more difficult to set. There isn't a hard end point at which to aim. Without instrumentation, the idea isn't to hit a specific light output level, but to remain below the point at which CRT wear and image fidelity worsen. Even with a light meter, one must still pay attention to colorimetry problems as well as absolute light output level. Since most of use don’t' run around with a colorimeter, we look for the point at which blooming appears because that is near the point of increased wear. Once the blooming point is determined on your display, it is taken as the maximal NOT desired setting for white level. Then, we set a viewing level somewhere below that point.
It appears that you are having difficulty detecting when blooming is happening on your display. The best advice I can give is to be VERY close to your screen -- perhaps two feet -- when looking for blooming. Doing this from normal viewing distance doesn't work as well. Turn white level down to a ridiculously low level. Make white actually appear gray. You should see distinct scan lines making up the picture. If you don't see sharp, distinct scan lines, then something is amiss with the display's focus adjustments. If that is the case, it needs to be serviced. You can't see the blurring effect of blooming if the beam is already defocused at low output levels.
I'll assume you're viewing HTT's Contrast Pattern or AVIA's Needle Pulses + Steps pattern or the Black Bars + Log Steps pattern. Look very carefully at the right edge of the rectangles which make up the steps pattern. Pay particular attention to the white rectangle and the one just below it. Turn up white level until you see the width of the white rectangle grow slightly larger. That is the point of blooming. Remember that point. Don't ever go over that point.
Now that you have found the maximum allowable white level. It's time to set viewing level. The lower, the better for CRT life, but you also need enough output to have a decent picture. Once again back white level down to a ridiculous level (making white look definitely gray). Increase white level until white appears white, but stay below the blooming limit which was previously determined. With any luck, white looks white before the point of blooming. If not, then your best course is to REDUCE AMBIANT LIGHT. It is better to adapt your eyes to make the lower level appear white than to overdrive the display to compete with excessive room light. This allows for best image fidelity within the limits of the display's capability. Some people will never control room light and turn up their displays beyond the point of blooming in order to view them in high ambient light. One is free to do so, but one must remember that this shortens display life and compromises image fidelity


--------------------------------------------------------------------------------

Guy Kuo - Video Test Designer
Ovation Multimedia Home of AVIA Pro, AVIA, and S&V Home Theater Tuneup

douglas-b

The short answer is..... set contrast to the LOWEST setting which still allows white to look white.

The long answer follows. This was written for AVIA but the basic principles still apply. Adjusting for just short of blooming is not the goal. Blooming is the point which should be thought as the red line for the electron guns. Just as you shouldn't keep your engine just below its red line in daily usage, you shouldn't do that with the contrast control of a CRT display. The on disc instructions for HTT and AVIA simply didn't allow time for as complete a discussion as follows. For those really wishing to do it as "right" as possible without instrumentation consider the following as superceding the on disc "instruction for the masses" on HTT, AVIA, and DVE discs....

......
Now for the more nebulous white level setting. You're quite right in noting that white level is more difficult to set. There isn't a hard end point at which to aim. Without instrumentation, the idea isn't to hit a specific light output level, but to remain below the point at which CRT wear and image fidelity worsen. Even with a light meter, one must still pay attention to colorimetry problems as well as absolute light output level. Since most of use don’t' run around with a colorimeter, we look for the point at which blooming appears because that is near the point of increased wear. Once the blooming point is determined on your display, it is taken as the maximal NOT desired setting for white level. Then, we set a viewing level somewhere below that point.
It appears that you are having difficulty detecting when blooming is happening on your display. The best advice I can give is to be VERY close to your screen -- perhaps two feet -- when looking for blooming. Doing this from normal viewing distance doesn't work as well. Turn white level down to a ridiculously low level. Make white actually appear gray. You should see distinct scan lines making up the picture. If you don't see sharp, distinct scan lines, then something is amiss with the display's focus adjustments. If that is the case, it needs to be serviced. You can't see the blurring effect of blooming if the beam is already defocused at low output levels.
I'll assume you're viewing HTT's Contrast Pattern or AVIA's Needle Pulses + Steps pattern or the Black Bars + Log Steps pattern. Look very carefully at the right edge of the rectangles which make up the steps pattern. Pay particular attention to the white rectangle and the one just below it. Turn up white level until you see the width of the white rectangle grow slightly larger. That is the point of blooming. Remember that point. Don't ever go over that point.
Now that you have found the maximum allowable white level. It's time to set viewing level. The lower, the better for CRT life, but you also need enough output to have a decent picture. Once again back white level down to a ridiculous level (making white look definitely gray). Increase white level until white appears white, but stay below the blooming limit which was previously determined. With any luck, white looks white before the point of blooming. If not, then your best course is to REDUCE AMBIANT LIGHT. It is better to adapt your eyes to make the lower level appear white than to overdrive the display to compete with excessive room light. This allows for best image fidelity within the limits of the display's capability. Some people will never control room light and turn up their displays beyond the point of blooming in order to view them in high ambient light. One is free to do so, but one must remember that this shortens display life and compromises image fidelity


--------------------------------------------------------------------------------

Guy Kuo - Video Test Designer
Ovation Multimedia Home of AVIA Pro, AVIA, and S&V Home Theater Tuneup