Basic Guide to Color Calibration using a CMS (updated and enhanced) - Page 16

Angryht, although I both saw that as well as read that I do not see how so doing sets the red, as well as the other primary colors, at their proper/target luminance level, unless the purpose is to get the relative luminance correct rather than the absolute luminance correct...put another way, is color decoding a function of ABSOLUTE or RELATIVE luminance and, based on n Tom's write-up, it would appear to be the latter....

Set color level relative to white, use any pattern level you like but 75% is typical.

Zoyd, thank-you and got it...it is the relative level that governs...

I am trying to set the grayscale my Toshiba CRT tube (34HF84), but the red levels are not tracking properly across the entire range. I was able to achieve nearly dead-on 6500k on the 30/90 patterns and get a Delta 0 reading, but the 50-70 range is showing a de-saturation of red to about 96 or 97%. I have a feeling it's caused by the "ROF" control which I accidentally set out of whack like a year ago.

When I boost the Red offset the mid-range is leveled out, but the 80-100 ire red gets oversaturated. If I boost the green and blue drives to compensate on the top end, the mid-range reds drop back to 97%. Any suggestions on which order I should adjust the RGB to correct this?

I have the following controls to work with (no red drive):

RCUT
GCUT
BCUT
GDRV
BDRV

ROF
GOF
YOF
others?

Any help is appreciated. Thanks.

Tom:

Although this should be obvious I want to make sure that I understand the nomenclature...in reviewing (and actually trying) your calibration method the following is unclear to me:

1. RE: Black Level -- what do you mean by peak white when explaining the calibration process...by peak white do you mean Y in fL for a 100 IRE white window?

2. RE: White Level -- what window/full field is displayed when determing the fL...is it a 100 IRE white window / full field?

TIA, noting that I searched the entire thread and could not find clear answers.

Tom, thank-you ever so much...

I just recieved my ca813 light meter and I wanted to take measurements but im confused on exactly how to use it. How do you take measurements from the screen with it? I want to find out contrast ratio and to take color measurements to fine tune the color decoder. I have a rptv. Any help would be appreciated. Thanks

On another topic, have you compared the CA813 absolute measurements to other probes? The reason I ask is when looking at the specs, the absolute accuracy stated is +/- 11% for a smooth illuminant, which means it could be even higher for other, non-well behaved SPD's, just curious.

Interesting, those were the comparisons of the color/white ratios correct? Some absolute errors can cancel in that ratio, what about the absolute numbers, how did the CA813 compare to the i1pro? Or maybe you can't do that since the CA813 is only calibrated for illuminance (lux) mode, correct?

Tom,
Being the super nice, swell, all around great guy that you are would you consider putting a 75% gray window on the super nice, swell, all around great calibration disc you have created? It would be useful for those of us using 75% RGB windows for color decoding.

And evidently it will get you anywhere fast... thanks for the addition!

Tom

Is it possible to create a 20/50/80 or 90 stimulus only pattern? I find that in the Mits DLP,that its hard to just use 20 and 80 because their parameters tend to effect non-linearly in the middle, so having all 3 available will help with some sets..

Tom:

In your description of calibrating color and tint the color is adjusted using ratio of Yred/Ywhite and the tint is adjusted using the xy values of cyan...that said, can you please explain why you use the value of Yred/Ywhite rather than Yblue/Ywhite as I believe -- AND POSSIBLY INCORRECTLY SO --that color control traditionally refers to blue and thus expected the use of Yblue/Yred.

TIA.

Tom, appreciate both the explanation and the quick response...not to mention the fact that I think the last peice -- at least at my current level -- has snapped into place...much thanks.

I have a couple of questions if someone could indulge me for a minute.

1.) I am getting different luminence readings from the 100% contrast pattern as opposed to the 100 IRE window. Aside from the fact that the Spyder2 readings seem to fluctuate while I am trying to measure the luminence, the 100 IRE window gives me a 116 reading compared to the 111 reading on the contrast pattern. It seems like the color saturation would be too low if I based it on the dimmer pattern. Which one is correct?

2.) After setting the right percentage levels, the points line up pretty well on the CIE diagram. The yellow dots line up almost dead-on for all colors except red and yellow. If I adjust the red, it throws off pink and yellow. Should I leave the settings so that pink and yellow are perfect but red is incorrect, or try and find a compromise between all three?

3.) The colors look good for the most part, besides being slightly undersaturated. The problem is that the block patterns on DVE now look way out of whack. If the CIE chart is correct, should I disregard the DVE pattern?

I don't have a jpeg of my measurements since I am at work, but any input would be appreciated. Toshiba CRT tube (34HF84).

Thanks.

By 100% contrast pattern do you mean a full 100% white field? If so, it would be normal to have lower luminance on a 100% white field compared to a 100% white window. But you shouldn't use 100% patterns for calibration anyway because that can cause several accuracy problems. You should use 75% patterns if you have them. And you should always use window patterns, not full field patterns for calibrating color and grayscale.

I am referring to the ref field at the end of the sequence of colored patterns on Tom's disc. It says 100% contrast on it and it is full field. I was getting a lower luminance reading than the IRE 100 window gave me.

Regardless, my main problem is with the color saturation. I set the color decoder according to the appropriate luminance percentages using the 100 IRE window. Even though the CIE color points are mostly dead-on (except red), the DVE color block pattern is all over the place. I don't know what is supposed to be correct.

Can the color decoder be alterd when I adjust the Gray scale tracking?

Why -- that is why 75% IRE and why a window over a full field?

TIA.

Tom does go on to say early in that posting to use WINDOW over full field..
What you want to read is 75% white(I dont think he actually says 100% white), then 75% color..pick the WINDOW patterns over full field windows..ALthough I think if you have FrontProjector, then a FULL wiindow will be better. For RearProj - then window should be used.

If you did use 100% window in white and read the Y luminance, then you have to make sure that your COLOR (R,G,B,C,M,Y) are 100% as well..they have to match each other in pattern..Stick with 75%white pattern window, then 75% Colors window

gregr, Tom

I think you should check both 75% and 100% decoding levels. Yes it is true that 100% patterns tend to blow white and decoding levels out - but don't you want to know that so you can turn down the contrast so that the 100% pattern becomes just as bright as your 75% patterns were so the problems go away?

If you don't calibrate for 100% - then half of the brightness you see won't be calibrated - it will still be annoying blowouts!

If you set the decoding levels with a 75% pattern as suggested. You could easily check if the contrast ratio is too high, with a 100% pattern, right? You can then adjust it accordingly to find the best setting.

Hey all...

This is in reference to one of my specific posts in another thread:

http://www.avsforum.com/avs-vb/showt...5#post12220805

So, in essence, I received my replacement one today and it seems to work right. But I have a specific question about the color decoder and not the program, so I feel it fits in more here.

Background: this is a Sony VPL-VW50 with over 1000 hours on the bulb. With the new colorimeter, I see a problem again with the color decoder. However, I am wondering if this is a problem with the DI implementation. I've gone through setting Red with DI auto and manual. With DI auto, there is no way I can get an appropriate 21% based off of white. Just isn't going to happen. However, with DI manually set, I can set color and tint just fine.

So, here's the question. Do I go ahead and set colors with DI manual and move it back to auto once done, or is there something else I should be doing. I must say it was much easier calibrating this time around, so it was definitely the broken i1 that was my problem.

I'll post more about the specifics in the other thread when I get a chance. Just wanted to deal with the general feeling regarding DI.

Thanks,
Ed