Basic Guide to Color Calibration using a CMS (updated and enhanced) - Page 13 - AVS Forum
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post #361 of 1936 Old 10-24-2007, 10:24 AM - Thread Starter
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Quote:
Originally Posted by awssvtt View Post

1. Is the Eye1 is sensitive enough to measure the 10IRE for brightness setting (0.63% of Y at 100%IRE). If not then the only option is to look at the moving bar for brightness setting. Correct?

No, it isn't. I'd get the CA 813 Light meter and point it towards the lens.

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2. For contrast setting, I got around 4fl with High Contrast Setting (IRIS). I could not increased the value of Y at 100IRE (increase fl) even at Max Contrast Setting. So the only option is to change the Z12k setting to High Brightness but at the expense of Contrast. Thus, a new bulb is needed only at aroung 500 Hrs. Is that the only option that I have?

Again, use the CA 813 to measure light output. Place at the screen plane facing towards the lens.

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3. Do I adjust brightness and contrast using the Z12K menu of I should set Brightness and Contrast at 0 setting and adjust these two parameters via setting Red Gain and Green Offset methodology.

I can only tell you what I do. To adjust Contrast and Brightness, use the Contrast and Brightness controls.

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post #362 of 1936 Old 10-24-2007, 11:52 AM
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Quote:
Originally Posted by awssvtt View Post

Hello Tom,

1. Is the Eye1 is sensitive enough to measure the 10IRE for brightness setting (0.63% of Y at 100%IRE).

Depends on what your actual luminance is that corresponds to 0.63%. At >100 nits (plasmas, LCDS, etc.) 0.0063 x 100=0.63 nits is easily measured by the i1pro as long as you average multiple measurements and perform the dark current offset correction. For FP set-ups at half that value it's still doable but your error bars are increasing quickly so you're probably better off moving to a direct reading using the CA 813. Tom, have you ever done a head-to-head between the 813 and the i1pro, I'd like to know in absolute units where they start to significantly diverge, say around the 5% level below 1 nit (0.05 nits). Previous measurements posted by umr with a PR-670 as reference indicated that below about (0.1 nits) the error bars > 10%. I think the manufacturer rates it to meet error requirements down to 0.2 nits.
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post #363 of 1936 Old 10-24-2007, 11:13 PM - Thread Starter
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Quote:


Tom, have you ever done a head-to-head between the 813 and the i1pro, I'd like to know in absolute units where they start to significantly diverge, say around the 5% level below 1 nit (0.05 nits). Previous measurements posted by umr with a PR-670 as reference indicated that below about (0.1 nits) the error bars > 10%. I think the manufacturer rates it to meet error requirements down to 0.2 nits.

Zoyd, no I haven't. I have a plasma and LCD calibration this weekend. I'll take a look.

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post #364 of 1936 Old 10-25-2007, 05:45 AM
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Hi,

Does anyone have or know where to get the SD color definitions xyY for PAL (EU). I think the SMPTE-C is for the NTSC system only.

Regards,

Kostas
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post #365 of 1936 Old 10-25-2007, 08:13 AM
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Quote:
Originally Posted by kopa13 View Post

Hi,

Does anyone have or know where to get the SD color definitions xyY for PAL (EU). I think the SMPTE-C is for the NTSC system only.

Regards,

Kostas

PAL/SECAM (EBU)
R: 0.6400 0.3300 0.222021
G: 0.2900 0.6000 0.706645
B: 0.1500 0.0600 0.071334
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post #366 of 1936 Old 10-25-2007, 06:20 PM
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Sorry if I have missed this somewhere here (I am pretty green on this calibration stuff) but when I use HCFR in xyY mode my Y calcuations don't even come close to the ref Y. I get numbers like 13.198 for red instead of around the 0.213 ref number. I am sure I am its something simple that I am missing.
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post #367 of 1936 Old 10-25-2007, 06:34 PM
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post #368 of 1936 Old 10-25-2007, 06:36 PM
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Quote:
Originally Posted by zoyd View Post

The 0.213 reference is a ratio, not Y. You want to divide Yred by Ywhite and get 0.213

Ah that makes sense. Thanks!
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post #369 of 1936 Old 10-25-2007, 07:24 PM
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Be sure to be consistent with the percent. In other words, if you are measuring 75 percent R, G, and B, use 75 percent white (75% amplitude/ IRE).

-Greg
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post #370 of 1936 Old 10-25-2007, 07:58 PM
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Here are my numbers on a Mits 73833 using a Spyder II (I know) and HCFR. This is from Toms 1994 sheet. Most of my dE variance seems to come from Saturation which the mits has no control of. Any ideas on correcting it?



Red 0.642 0.332 0.211 6.4% 30.3% 63.3% 0.9
Green 0.300 0.622 0.736 6.9% 71.5% 21.6% 2.2
Blue 0.152 0.065 0.071 2.1% 81.0% 17.0% 1.4
Cyan 0.203 0.327 0.800 4.0% 95.5% 0.5% 4.4
Magenta 0.323 0.140 0.290 2.3% 91.8% 5.9% 2.9
Yellow 0.428 0.522 0.935 1.8% 90.3% 7.9% 2.8
LL
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post #371 of 1936 Old 10-27-2007, 05:51 AM
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Quote:
Originally Posted by zoyd View Post

PAL/SECAM (EBU)
R: 0.6400 0.3300 0.222021
G: 0.2900 0.6000 0.706645
B: 0.1500 0.0600 0.071334

Thanks Zoyd. What about White(D65) xyY and the secondaries values? I know there is a relation between the primaries and the secondaries (ie a percentage or substraction) but I don't remember it

Regards,

kopa13
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post #372 of 1936 Old 10-27-2007, 06:19 AM
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Quote:
Originally Posted by kopa13 View Post

Thanks Zoyd. What about White(D65) xyY and the secondaries values? I know there is a relation between the primaries and the secondaries (ie a percentage or substraction) but I don't remember it

Regards,

kopa13

D65 is D65, it doesn't change with gamut and white Y=1.0. Secondary Y calculate from primary Y (C=B+G, etc.).
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post #373 of 1936 Old 10-29-2007, 03:55 PM
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Is it right that we are most sensitive to +Green in an image. Or am I wrong here. It's worse to have some +green in the grayscale tracing than a over saturated green in the gamut?
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post #374 of 1936 Old 10-29-2007, 05:56 PM - Thread Starter
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My understanding is that the eye is most sensitive to green in low light and most sensitive to red in well-lit environments. Because of the large role that red plays in getting skin tones right, I find that it is most important to get red right in the grayscale with green just behind. Errors in blue are the least troublesome.

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Is it right that we are most sensitive to +Green in an image. Or am I wrong here. It's worse to have some +green in the grayscale tracing than a over saturated green in the gamut?


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post #375 of 1936 Old 10-29-2007, 11:44 PM
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Quote:
Originally Posted by TomHuffman View Post

My understanding is that the eye is most sensitive to green in low light and most sensitive to red in well-lit environments. Because of the large role that red plays in getting skin tones right, I find that it is most important to get red right in the grayscale with green just behind. Errors in blue are the least troublesome.

I'm following your reasoning. The middle scale of the gray's is most importat to get right, escpecially with Red, next after is green n the lows. Last place high part of the grayscale.
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post #376 of 1936 Old 10-30-2007, 09:17 AM
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Quote:
Originally Posted by TomHuffman View Post

The Sony doesn't have a CMS.

Could you comment on this calibration report on a Sony A3000? If there is no CMS, then does Sony have some other approach? How was this done?

http://www.avsforum.com/avs-vb/showt...0#post12008400

umr also said in response to a question about how to duplicate the calibration,

"You would need my $24,000 spectroradiometer to do it. It is pointless for me to tell you how. Measuring colors on displays like this that support xvYCC color space is incredibly challenging and requires the highest level instrument to do a credible job."
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post #377 of 1936 Old 10-30-2007, 10:07 AM - Thread Starter
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The primaries on the before/after charts are almost identical. The difference was that the secondaries were more accurate after calibration. That comes from improved grayscale tracking. The grayscale and color decoding impact the secondaries. You need a CMS to adjust the primaries.

As to the pointlessness of explaining the process and the need for a $24,000 piece of equipment to do it, let's just say I take a rather different view of these things.

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Could you comment on this calibration report on a Sony A3000? If there is no CMS, then does Sony have some other approach? How was this done?

http://www.avsforum.com/avs-vb/showt...0#post12008400

umr also said in response to a question about how to duplicate the calibration,

"You would need my $24,000 spectroradiometer to do it. It is pointless for me to tell you how. Measuring colors on displays like this that support xvYCC color space is incredibly challenging and requires the highest level instrument to do a credible job."
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post #378 of 1936 Old 10-30-2007, 11:08 AM
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Quote:
Originally Posted by kjgarrison View Post

"You would need my $24,000 spectroradiometer to do it. It is pointless for me to tell you how. Measuring colors on displays like this that support xvYCC color space is incredibly challenging and requires the highest level instrument to do a credible job."

It's also a deceptive statement because it implies he did move the primaries (because he thinks that's what you think) when as Tom pointed out all he did was balance the grayscale. If he had been able to adjust the primaries they would lie precisely on top of their targets. Grayscale tracking is not as demanding a calibration task for a probe as CMS calibration because white SPD's (spectral power distributions) are better behaved than isolated primaries.

btw, the improvement in primary color accuracy, which is not included in the report, went from
dE RGB:10.9,5.1,3.5 to 9.2,2.2,2.8 which is marginal at best.
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post #379 of 1936 Old 10-30-2007, 11:38 AM
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Quote:
Originally Posted by TomHuffman View Post

The primaries on the before/after charts are almost identical. The difference was that the secondaries were more accurate after calibration. That comes from improved grayscale tracking. The grayscale and color decoding impact the secondaries. You need a CMS to adjust the primaries.

As to the pointlessness of explaining the process and the need for a $24,000 piece of equipment to do it, let's just say I take a rather different view of these things.

Oh, I see. Very interesting. No magic involved. The primary colors for at least that particular set were pretty good to begin with.

Thank you.

I love this thread. It's kinda like reading Scientific American, fascinating but pretty much incomprehensible for us noobs.
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post #380 of 1936 Old 10-30-2007, 05:14 PM
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Tom,

Great thread for us beginners. I have Sharp 12K MKII and Colorfacts 6.0 Pro. I'm still learning to us it. Anyway I have read through the whole thread and I get the jist of the procedures. I have one question. In the Sharp CMS you have Gain, Offset and Gamma. WHEN and HOW do I adjust the gamma setting. I'm coming over from CRTs and normally we would adjust our RGB Gain pots to try to achieve an even cutoff point for all three tubes. This was more or less setting Gamma. If Gamma pots was to low, you would lose shadow detail. If to high, you would wash out shadow detail and have a slight glow on screen. Then we went on into calibrating the gains and cuts. Is it the same for the DLP gamma setting on my Sharp?

Thanks

Andre
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post #381 of 1936 Old 10-30-2007, 06:06 PM
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ALL,

Does anyone know anything about the TOPCON BM-7 Luminance Colorimeter? Any info would be great.

Thanks All

Andre
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post #382 of 1936 Old 10-30-2007, 07:16 PM - Thread Starter
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The GRB Gamma adjustments just adjust the grayscale throughout the entire range, whereas the RGB Gain is for the top end and the RGB Offset is for the low end. I find the Standard Gamma preset to be just about right for the Sharps. Use the items in the Gamma menu to adjust grayscale tracking.

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Tom,

Great thread for us beginners. I have Sharp 12K MKII and Colorfacts 6.0 Pro. I'm still learning to us it. Anyway I have read through the whole thread and I get the jist of the procedures. I have one question. In the Sharp CMS you have Gain, Offset and Gamma. WHEN and HOW do I adjust the gamma setting. I'm coming over from CRTs and normally we would adjust our RGB Gain pots to try to achieve an even cutoff point for all three tubes. This was more or less setting Gamma. If Gamma pots was to low, you would lose shadow detail. If to high, you would wash out shadow detail and have a slight glow on screen. Then we went on into calibrating the gains and cuts. Is it the same for the DLP gamma setting on my Sharp?

Thanks

Andre


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post #383 of 1936 Old 10-31-2007, 03:50 AM
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Quote:
Originally Posted by TomHuffman View Post

The GRB Gamma adjustments just adjust the grayscale throughout the entire range, whereas the RGB Gain is for the top end and the RGB Offset is for the low end. I find the Standard Gamma preset to be just about right for the Sharps. Use the items in the Gamma menu to adjust grayscale tracking.

Tom, a naive question but what exactly do you mean by the terms "top end" and "bottom end"...for example, does "top end" mean "add white" while "bottom end" means "add black"?

Thanks.

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post #384 of 1936 Old 10-31-2007, 06:11 AM - Thread Starter
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Quote:
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Tom, a naive question but what exactly do you mean by the terms "top end" and "bottom end"...for example, does "top end" mean "add white" while "bottom end" means "add black"?

Not quite. By top end and bottom end I mean the brighter part of the gray scale and the darker part of the grayscale respectively. You add or subtract amounts of RGB to ensure that both are neutral gray, or as close to it as possible.

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post #385 of 1936 Old 10-31-2007, 06:50 AM
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Quote:
Originally Posted by TomHuffman View Post

Not quite. By top end and bottom end I mean the brighter part of the gray scale and the darker part of the grayscale respectively. You add or subtract amounts of RGB to ensure that both are neutral gray, or as close to it as possible.

Tom:

Appreciate the response but I am guess that I am a little "brain dead" this moring...must be result of too much travel lately.

While I understand that (i) gray, as in the colour, is the combinations of various amount of RGB and (ii) 0 IRE to 100 IRE is the same gray (read combination of RGB) with difference brightness/luminace I still am puzzled as to the meaning.understanding of:

-- brighter part of the gray scale; and
-- darker part of the gray scale.

With that is a possible nivices interpretation that "brighter part of the gray scale" means brighter combinations/portion of RGB while the "darker part of thh gray scale" means the darker combinations/portion of of RGB where brighter and darker refer to chromaticity (i.e. exclude luminace).

TIA.

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post #386 of 1936 Old 10-31-2007, 08:09 AM - Thread Starter
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Brighter: 80-100 IRE, Darker: 10-30 IRE

Quote:
Originally Posted by Joelc View Post

Tom:

Appreciate the response but I am guess that I am a little "brain dead" this moring...must be result of too much travel lately.

While I understand that (i) gray, as in the colour, is the combinations of various amount of RGB and (ii) 0 IRE to 100 IRE is the same gray (read combination of RGB) with difference brightness/luminace I still am puzzled as to the meaning.understanding of:

-- brighter part of the gray scale; and
-- darker part of the gray scale.

With that is a possible nivices interpretation that "brighter part of the gray scale" means brighter combinations/portion of RGB while the "darker part of thh gray scale" means the darker combinations/portion of of RGB where brighter and darker refer to chromaticity (i.e. exclude luminace).

TIA.


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post #387 of 1936 Old 10-31-2007, 08:55 AM
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Quote:
Originally Posted by TomHuffman View Post

Brighter: 80-100 IRE, Darker: 10-30 IRE

Tom:

So, in other words, the gain/offset controls add and subtract the amount of gray with high luminance (i.e. 80-100 IRE*)/low luminance (i.e. 10-30 IRE*) to a given IRE window (say, 50 IRE) so that the combination (i.e. 50IRE to gain + offest) results in the desired color temperature (say, 6500K) for the given window....do I now get it?

* The only difference between IRE windows is the brightness/luminance...that is, all IRE windows have the same chromaticity but different brightness/luminance.

TIA.

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post #388 of 1936 Old 10-31-2007, 10:06 AM - Thread Starter
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Again, not exactly. They would add/subtract gray, only if you adjusted the RGB controls in tandem. Typically, you would adjust one or more of these controls to get neutral gray, i.e., if it measures too much red at the bottom, then lower the R offset control. If it measures too little blue at the top end, then raise the B Gain control. You want a balance of RGB throughout the entire range.

The issue of raising or lowering the amount of gray has to do with gamma, which is a related concept. Each level 10-90 IRE should have a prescribed level of brightness (forgetting now the color balance) to achieve a desired gamma curve.

Gamma is to the grayscale what color decoding is to the gamut.

Quote:
Originally Posted by Joelc View Post

Tom:

So, in other words, the gain/offset controls add and subtract the amount of gray with high luminance (i.e. 80-100 IRE*)/low luminance (i.e. 10-30 IRE*) to a given IRE window (say, 50 IRE) so that the combination (i.e. 50IRE to gain + offest) results in the desired color temperature (say, 6500K) for the given window....do I now get it?

* The only difference between IRE windows is the brightness/luminance...that is, all IRE windows have the same chromaticity but different brightness/luminance.

TIA.


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post #389 of 1936 Old 10-31-2007, 10:57 AM
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This stuff is complicated and my heads feels as though it is going to explode...that said, here goes another kick at the can...

Quote:
Originally Posted by TomHuffman View Post

Again, not exactly. They would add/subtract gray, only if you adjusted the RGB controls in tandem. Typically, you would adjust one or more of these controls to get neutral gray, i.e., if it measures too much red at the bottom, then lower the R offset control. If it measures too little blue at the top end, then raise the B Gain control. You want a balance of RGB throughout the entire range.

I understand that when performing a gray scale calibration that for each IRE window one want to achieve, among other things, a given chromaticity/color and a given luminance/brightness such that the resulting color temperature is 6,500K -- right?

I also understand that, asuming that the luminance/brightness is correct, that the chromaticity is adjusted by adding/subtracting amounts of red, green and blue -- right?

I do not undersatnd the use of the terms "bottom end" and "top end"...is it as simple as:

a) offsets are used to adjust the chromaticity for the lower IRE windows; and
b) gains are used to adjust the chromaticity for the higher IRE windows?

If yes, then where is the magic cutoff point and why?

If no, then I am still lost...not a comfortable feeling.


Quote:
Originally Posted by TomHuffman View Post

The issue of raising or lowering the amount of gray has to do with gamma, which is a related concept. Each level 10-90 IRE should have a prescribed level of brightness (forgetting now the color balance) to achieve a desired gamma curve.

I wil tackle this one next...that said, I understand (or, at least think I do)that each level of 10-90 IRE should have a prescribed brightness as it is the combination of color/chromaticity and brightness/luminance that produce the 6,500K...that said, I am lost as to how gamma fits in!


Quote:
Originally Posted by TomHuffman View Post

Gamma is to the grayscale what color decoding is to the gamut.

Also an issue for another day....

Thanks for everything...much appreciated..

Joel
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post #390 of 1936 Old 10-31-2007, 11:55 AM - Thread Starter
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Quote:
Originally Posted by Joelc View Post

I understand that when performing a gray scale calibration that for each IRE window one want to achieve, among other things, a given chromaticity/color and a given luminance/brightness such that the resulting color temperature is 6,500K -- right?

The only color relevant to the grayscale is white, which should be 0.3127, 0.329. I would avoid using the term "color temperature". This is a shorthand way of referring to the appropriate balance of red and blue, but it ignores green. So you could have a color temperature of 6500k and the color of white could appear too green or magenta. Stick to D65 or 0.3127, 0.329 as a way of describing the target color of white.

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Originally Posted by Joelc View Post

I do not undersatnd the use of the terms "bottom end" and "top end"...is it as simple as:

a) offsets are used to adjust the chromaticity for the lower IRE windows; and
b) gains are used to adjust the chromaticity for the higher IRE windows?

If yes, then where is the magic cutoff point and why?

Yes, it is that simple. There is no "magic cutoff". An offset primarily adjusts 10-30 IRE, but it has a smaller affect above that. A gain control primarily adjusts 80-100 IRE but will have a smaller affect below that. The precise affect they have will only be seen by direct measurement. That's why you may have to go back and forth several times to get it right--they often have interactive effects.

Tom Huffman
ChromaPure Software/AccuPel Video Signal Generators
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