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post #31 of 37 Old 12-01-2008, 12:05 AM
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Originally Posted by TomHuffman View Post

I haven't responded because I have been on Thanksgiving vacation and not following the thread.

I really don't understand why these debates cannot remain respectful and without personal animus. It is not personal. It was not my intention to question your "honor" and I'll ignore your unhelpful assertions about what I do and do not understand.

Okay, so how doesn't your method of eliminating color error overestimate dE at, say, 30% for a given absolute difference in u' and v'?

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Of course, the CIELUV and CIELAB specifications include consideration of the brightness of the measured sample compared to a reference. This is because the colors in a gamut include a specified level of brightness. Thus, a measured color whose brightness deviates from that reference has a higher dE than one that doesn't. However, the same cannot be said for white.

White is, um, definitional. It's a normalization thing. Yn == 1.0.

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The basis of this debate is stated in your claim that "To compute dE, you would need to specify a measured Y (normalized) and an assumed gamma to compute dE in the above situation."

That is the entirety of this argument: should an assumed gamma and a measured Y be included in dE calculations for grayscale.

Good. This is where it gets fun, because the "real" "debate" seemed to be whether eliminating gamma error was a good thing, and since that debate is settled, let's talk specific implementations.
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Note: we need an assumed gamma because this the ONLY sense in which we could assume a "correct" level of brightness for white.

White is white. It's a definitional thing. ALL luminance values need to be normalized against the luminance for white, which is 1.0 (what "normalization" means).
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Unlike color, the definition of white includes no specific level of brightness. Indeed, the specified level of brightness for color is defined relative to the brightness of reference white, which is NOT defined in advance.

Wow. Simply wow. Which definition of color includes a specific level of brightness? Is red like 3.14159 ftL? Does it turn magenta when it gets to 9 ftL? Does color care whether you are in metric or imperial measures?

Here's a hint: all luminance values need to be normalized against white. That is the definition. As a result of this, gamma is undefined at Yn = 1.0.

Now gray, on the other hand does depend upon what flavor of gray you are trying to produce. In other words, you need to know some things about what was intended versus what was actually produced.

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So this all boils down to whatever reasons one can offer for or against including a measured Y and an assumed gamma in one's dE calculations for grayscale. The reasons against, as I have suggested, are compelling. Let me enumerate them:

1. Unlike color, there simply is no specification for the "correct" level of brightness for white. There is only what the target gamma specifies.

I'm done chiding you for being sloppy on distinguishing gray from white. The "correct" level of gray is a combination of the target gamma formula, the target exponent and the signal level.

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2. There is not even any fixed definition of the "correct" gamma. This is both because there is more than one way to calculate gamma and because gamma requires assumptions about viewing environment and the characteristics of the display on which the content is mastered.

Good reasons to eliminate gamma error, but then computing gamma error, if it is so unknown, should be pretty tough, huh?

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3. The methodology you suggest

You have clearly demonstrated that you do not know this.
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is a literal application of the CIE specification for a context in which it was never intended.

Huh? They did not know about gamma and grayscale in the 70s?
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The CIE specification is intended for grading color difference,

Of which, grayscale is an example.
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not for grayscale tracking, which poses a different set of issues.

Such as?? I'm really curious. This is stuff that seems not to have been included in the SMPTE Journal.

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4. The methodology you suggest is inconsistent with industry standards. There is no other source I am aware of that calculates grayscale error in the way you describe.

Aside from the CIE, right? But hey, what do they know? In other words, show me how you aren't overestimating error? Or concede that it is something you aren't worried about.

By the way, which method are we talking about, again? I'm not sure since I'm pretty sure we have not disclosed our actual algorithm, pretty much ever. And we most assuredly have not done so in this thread.
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ColorFacts does not.

We take pride in having deployed things like point gamma calculations years before they did. This really isn't any different.
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Greg Rogers' Display Calibration Calculator does not.

Greg generally uses dE(uv).
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ISF recommends that it is MORE important to get the low end of the grayscale right rather than LESS important as you seem to suggest.

You are making this too easy:
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Originally Posted by TomHuffman View Post

What's wrong with the ISF description of color?

I am a graduate of the ISF seminar, and I think that the organization has performed a valuable service at educating the public about the importance of accurate video. However, the ISF understanding of color is not entirely clear.

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Cliff Plavin of Progressive Labs has always argued for dC only for grayscale. I have resisted this, because although I agree that dL should be ignored, I didn’t see any reason to ignore dH. However, when you look at the actual data, the contribution of dH to grayscale errors is negligible. Thus, I now think this is a defensible position.

Really? You think that dE76 doesn't encompass dH inside dC? Would it surprise you to learn that it does?
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The one you advocate here is not. If you are aware of any other reputable source that calculates grayscale dE the way you advocate here, then I'd sure like to know.

This is getting pedantic, but the only methods I have talked about are either a) the standards themselves, or b) people's specific "adjustments" to them.

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5. This methodology has the effect of systematically and sometimes grossly understating grayscale error. One might argue the point because of the eye’s poor sensitivity to color at very low light conditions, as was suggested in the original post's irrelevant discussion of scotpic, mesopic, photopic vision. But as I pointed out, the level of illumination required for this phenomenon to matter is much lower than any grayscale reading would ever include. Nonetheless, you apparently continue to endorse the view that we should calculate the dE of a specified white, say x0.314, y0.351, differently at 90% stim than at 100% stim where our variable sensitivity to color perception is surely irrelevant.

Tom - Please stop. Seriously. Reading comprehension is not your strong suit. I'm having fun picking this apart, but now you are embarrassing yourself.

So that we are clear: the method should be constant across any set of numbers. The output is what changes based upon the inputs. All that I posted, above, was a set of numbers that were straight CIE76 with dL = 0 and a constant du' and dv'. That's all. The point was to demonstrate a desirable property of color error that was intended by the CIE, and that also shows up in CIE94 and CIE00. It is this property that our little trick preserves, while eliminating gamma error. No, we do not aribtrarily set dL to 0.

The rest of this is simply demonstrating that despite having published a dE calculator of your own, you do not really understand what goes on in the numbers. Your complaint, in this case, is with the CIE itself, not us..

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Your own example has the dE of the SAME COLOR OF WHITE dropping nearly 2 points for no other reason than from going from 100% to 90% stim and reduced by more than half at 40% stim.

Yep. The numbers are what they are, it's not our method. In fact, it is a lot closer to yours. The only thing I did was let L* vary, rather than hold it constant to show how the CIE intended the equation to work. Obviously, you did not recognize that.

If you think it is as easy to see a given color difference when there is approx. 1/7th - 1/10th as much light around as what you are adapted to for white then that sounds like a testable hypothesis. One might even develop a model, of people's color perception. Here's a hint: if you want to be taken seriously, don't use your "sunlight/inside light" example from your WSR article. That one was simply bad.

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I frankly find it difficult to even take this very seriously. It appears to arise from a rigid application of a mathematical model without regard to the consequences for practical application much less common sense.

What consequences are there for practical application? That you set a high hurdle for imperceptibility? That you have to rely on software that does all of the computation for you in real time? That our users have to toggle a control if they want to use it? Do tell. I'm curious here, too.

As for common sense: I'm all ears. I'd really be entertained to learn why you prefer tool vendors who were fast-and-loose with published standards.

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Consider the following. Assume a 35 fL peak output, 2.2 gamma display. Also assume a consistent white of x0.314, y0.351. This is the white point for DCI. Now what’s the dE of this white relative to a Rec. 709 reference of x0.3127, y0.329? According to the methodology you endorse here, at 100% stim it is 17.5 (you get a slightly different number I suppose because of rounding differences), but at 20% stim it is 3.4, well within the SMPTE’s recommendation of a dE of no more than 4.0 L*a*b* units. So, using your recommended methodology, x0.314, y0.351 at 20% stim is a perfectly acceptable calibration result.

Careful, you are perilously close to saying that SMPTE uses L* when computing dE (you would be right there, though individuals vary in interpretation as this thread demonstrates). However, your math is off. Let's leave aside Lab76 alone until we master Luv. In CIE76 or CIE94 terms, it is over 9.

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Here’s the RGB values for that color of white.

Our numbers match here.

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Bill, this is madness.

Agreed.
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Are you really telling your customers to not bother with an error this large at the low end of the grayscale because our eyes just won’t be sensitive to it?

No.
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Here’s a simple experiment. Just look at a 20% (approx. 3.5 cd/m2) window or field of x0.314, y0.351. If you can’t tell the difference between that and another window or field of x0.3127, y0.329 then getting your display calibrated is the least of your worries.

Agreed. However, your "simple experiments", judging by the WSR article, often involve such "minor nuisances" as significant changes in ambient light spectrum and luminous flux, so one does have to double-check these things.

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6. This recommendation isn't even internally inconsistent. Surely you do not also advocate using a different set of standards for judging the dE of pri/sec colors when using 75% windows as opposed to 100% patterns. But you should to be consistent with your view that the eye becomes progressively less sensitive to color at lower light levels and that the dE measurement should reflect this.

Huh? It does, and so does yours, unless you use dE(uv) for gamut work. We recommend people turn off gamma correction when doing primary/secondary work. This was discussed previously.

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If you did then, all else being equal, a color of red at 75% should have a lower dE than the same color of red at 100% stim.

A given absolute difference in chromaticity would be less visible at lower light levels. Whether it drops below the threshold of visibility is another matter. This is curious from someone who just published something on the underappreciated nature of brightness in color measurement. Ironic, even.

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Of course, you don’t advocate this because the brightness of color is judged against white as a reference, which changes proportionally. But that’s the point, isn’t it? The brightness of white is relevant for gamma, levels, and calculating the dE of color. It is NOT relevant for calculating the dE of itself.

Huh? Are you confusing white, which is a point, with gray, which is a line connecting white and black? If white changes, then the entire adaptation model changes (must be re-normalized). Luminous flux is captured in the "Lightness" component of color error. You really don't understand this, do you?

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You seem to want to make the narrow point that IF you include a measured lightness element and assumed gamma in dE calculations that you get the result you describe. I don’t question this result. What I question is whether this approach offers a reasonable calibration methodology or sound color science.

Gauntlet thrown; gauntlet accepted. I am now free to post my critique of your CMS document. Hilarity will ensue.

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BTW, Grassmann's Law explains why the brightness of RGB equals the brightness of white and why the brightness of each of the secondaries equals the brightness of the contributing primaries. That was not the issue I mentioned, which was the relative brightness (relative to each other and relative to the original white at the same level of stimulus) of the grays that result after removing all of the chroma from color signals.

Tom - Here's a clue, as in "let me spell it out for you":

The additive mixture of primaries is an algebraic property between the defined primary locations and the white point. If your white point is constant (say, D65), but your primaries deviate from the established standard, then a change in the relative mix of the primaries will change the amount of total light, aka Grassman's law. When you change a saturation control, you are changing the relative mix of these primaries (note my red desaturation example, above). In other words, whether the predicted "no change" in luminance actually occurs is entirely dependent upon the actual locations of the primaries.

This application of Grassman's law is, I suspect, more advanced than your understanding since your CMS document includes the contradictory admonishments to set red to as close to 21% as possible using a saturation control, while not using color decoder controls to change the gamut. However, we'll give you a head start to make wholesale changes. It's late, and I am now bored with this utterly and thoroughly.

Bill

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post #32 of 37 Old 12-01-2008, 12:56 AM
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Originally Posted by TomHuffman View Post

Bill, you are just making this stuff up. Please refer us to where I defined "saturation", incorrectly or otherwise. What we mildly disagreed about was the definition of chroma, which you are apparently confusing with saturation. I defined chroma as "colorfulness of a color relative to a sample of white at a similar level of illumination." Here's how Fairchild defines chroma "Colorfulness of an area judged as a proportion of the brightness of a similarly illuminated area that appears white. . ." [Color Appearance Models, p. 103]. Here's how Schanda defines chroma: "Colorfulness of an area judged as a proportion of the brightness of a similarly illuminated area that appears white. . ." [Colormetry: Understanding the CIE System, Glossary, p. 445]. The two online references I provided offered similar definitions. I could go on. However, if I were to define saturation it would be either "colorfulness relative to its own brightness", or, more simply, "distance from the white point on a CIE chart."

Tom - Please read. Really. Please read. What I said, above, was, essentially, that chroma has different meanings depending upon context, and these contexts have important and very different distinctions. To a video engineer, chroma is the color difference signal which pairs with luma. Poynton, chapter 11; I especially like the margin note on page 94 ("The video literature often calls these quantities chrominance. That term has specific meaning in color science, so in video I prefer the term modulated chroma.") The point here is that if you use chroma to mean both, then you need to be really clear about what it is you are talking about.

Please show me, in my quotes, where I confused chroma and saturation, with chroma as you define it. I'm waiting. I found this particularly cute in your wikipedia article:

"With three attributescolorfulness (or chroma or saturation), lightness (or brightness), and hueany color can be described." (emphasis mine)

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A strawman is when one incorrectly characterizes his opponent's position or argument so as to make it seem less plausible than it really is. The only position that I attribute to you for the purpose of this argument is the one I quoted directly, namely that "To compute dE, you would need to specify a measured Y (normalized) and an assumed gamma to compute dE in the above situation."

To which situation, then do you think I was referring? And which attributes did you attach to it?

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I feel a need to remind everyone that assertion is not the same as argument. I gave a series of reasons for why one should not use an assumed gamma and measured brightness in dE calculations for grayscale in my latest post, including examples of others who I guess you think are similarly mistaken. Instead of responding, you simply assume the truth of the very position in dispute and offer a series of truncated quotes from earlier posts, which has the overall effect of making it rather difficult to make sense of this latest post.

Irony, Tom, irony. That post was my frustration that you were not actually reading nor responding directly to what I wrote. The post afterwards, which was much longer, took longer to write.

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It seems silly to you because you apparently don't understand the difference between chroma and saturation. I refer you to the sources I have already cited--online and published hardcopy--for clarification. I will gladly provide others.

You mean the variable one you used initially, or the ones that repeat the definition you called, what was it, hazy?
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Originally Posted by TomHuffman View Post

The theoretical part is a little hazy because even the passage I quoted concedes that the definition of chroma varies depending on the context.

I understood it. At one point, you even believed that I did:
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Originally Posted by TomHuffman View Post

BTW, it occurs to me that this is just another way of stating the point you made in your post that the eye sees more color at higher levels of illumination.

In fact, you were perilously close to saving yourself my preceding post about how the dE equations work if you could have connected your quote, immediately above, with this:
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Originally Posted by TomHuffman View Post

Of course, color perception is less acute at low light levels than at higher light levels, but I still don't see how this is relevant to measuring grayscale dE error UNLESS the formula you use compares the actual measured L against the ideal L for a specified level of stimulus.

This all might have been over.

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I am often amused by the extremely technical and razor thin distinctions that we often obsess over in this forum. Debates about whether we should use 2.5 or 2.2 as a target gamma is one example. Kraz and I have debated intensely about whether to use CIELUV or CIELAB. The thing is, these are relatively small distinctions. What is breathtaking about this debate is that the methodology that you endorse renders truly enormous grayscale errors perfectly acceptable.

If you could calculate them correctly, I'd understand, but the sub-text of the argument is that, well, you don't.

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I asked before, and you chose not to respond. Can you cite any other reputable source that would grade a 20% stim (3.5 cd/m2) grayscale reading of x0.314, y0.351 as within acceptable dE tolerances for a Rec. 709 reference?

Asked and answered. >9 is not acceptable.
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Since you obviously have no respect for my view on the subject

Not any longer.
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and don't seem particularly interested in the sources I cite, then perhaps Greg Rogers' Display Calibration Calculator (http://www.accupel.com) might interest you.

He uses dE(uv). We covered this.

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You would suggest that it would be perfectly valid to grade the grayscale dE error at 20% stim as 3.4, instead of 17.5. This is not a minor technical discrepancy. This is night and day.

Agreed, but this has been a tutorial, of sorts, on calculating dE. I hope you learn the lesson.

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BTW, one correction. It turns out that Grassmann's Law can explain the phenomenon I was describing.

Hallelujah!
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The luminance of the 3 primaries turned into gray will equal 255 in RGB.

So close. Yet so far.
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The proportions are R0.299, G0.587, B0.114, which equal 1.0. However, I still don't see it in CIE Y.

Use the custom white point function in ColorFacts, since I assume this has put you off of our stuff, to compute what your color mix is for a given set of real primaries. Then draw a big circle around those values to account for 4%+ measurement error in luminance. Try a little harder; you may get there.

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post #33 of 37 Old 01-09-2009, 02:08 AM
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Quote:
Originally Posted by Bear5k View Post

Okay, so how doesn't your method of eliminating color error overestimate dE at, say, 30% for a given absolute difference in u' and v'?

Please stop referring to this as "my" method. This the method that the entire industry, so far as I can tell, except for you, uses for gray scale grading.

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Originally Posted by Bear5k View Post

Good. This is where it gets fun, because the "real" "debate" seemed to be whether eliminating gamma error was a good thing, and since that debate is settled, let's talk specific implementations.

This leaves me speechless. Bill, I cannot imagine where you would have gotten the idea that this debate was ever about whether "eliminating gamma error was a good thing."

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Originally Posted by Bear5k View Post

Wow. Simply wow. Which definition of color includes a specific level of brightness? Is red like 3.14159 ftL? Does it turn magenta when it gets to 9 ftL? Does color care whether you are in metric or imperial measures?

This misinterpretation of what I wrote is so bizarre that I can only assume that it is intentional. Yes, the definition of red includes a specific level of brightness. What is that level? Well, for Rec. 709 it is 21.26% of reference white. Now is it remotely possible that you didn't understand that this is what I was referring to, or were you intentionally mischaracterzing my well-known and often-repeated view just to try to score a point? What was it you referred to earlier? Straw man? This is a textbook example.

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Originally Posted by Bear5k View Post

You have clearly demonstrated that you do not know this.
Huh? They did not know about gamma and grayscale in the 70s?
Of which, grayscale is an example.
Such as?? I'm really curious. This is stuff that seems not to have been included in the SMPTE Journal.

Your unfortunate habit of responding individually to snippets of text rather than the entire pasage (or even complete sentence) makes responding to this difficult. Basically, I would just repeat what I said above. CIE has never, to my knowledge, published standards for how to implement dE specifically in grayscale tracking. That's not what they do. The implementation of CIE standards is up to individual industries.

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Originally Posted by Bear5k View Post

By the way, which method are we talking about, again? I'm not sure since I'm pretty sure we have not disclosed our actual algorithm, pretty much ever. And we most assuredly have not done so in this thread.

Bill, you really can't have it both ways. You cannot one moment refer to CIE standards and then in the next breath refer to "our actual algorithm" as though you have implemented something proprietary with respect to dE and grayscale tracking. The CIE dE formula is widely published and relatively simple. Our debate is about the implementation of that formula in grayscale tracking. Presumably we use the same forumla, except that your implementation of it--at least one version--includes the actual measured Y values which are compared against what the target gamma says they should be at each level of stimulus.

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Originally Posted by Bear5k View Post

Greg generally uses dE(uv).

Not just Greg. This or dE(ab) is what the enture industry uses for grayscale dE. That's what we are arguing about. I don't use the label dE(uv) or dE(ab) because I think people find it confusing. BTW, CIE never, so far as I know, endorsed anything called dE(uv), which is a perfect example of how individual industries adapt CIE standards to suit their own needs.

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Originally Posted by Bear5k View Post

You are making this too easy:

Are doing this on purpose? I can't quite tell if you are having us on at this point. In an attempt to show that I have contridicted myself, you quote me citing ISF one place and criticizing them another place. Unfortunately, for anyone who cares to read the full passage, which you (again) quote only the first couple of sentences of from an entirely different thread without any indication where this comes from, they will see that my criticism of ISF has to do with their vague distinction between color accuracy and color saturation. I cite them approvingly here for their training about the importance of getting the low end of the grayscale right. Is it possible for ISF to be mistaken in one area and correct in another? I think so.

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Originally Posted by Bear5k View Post

Really? You think that dE76 doesn't encompass dH inside dC? Would it surprise you to learn that it does?

No, Bill, it does not surprise me. I guess I don't see your point.

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Originally Posted by Bear5k View Post

This is getting pedantic, but the only methods I have talked about are either a) the standards themselves, or b) people's specific "adjustments" to them.

I asked a specific question, a question that you refused to acknowledge, must less answer. I'll ask it again. Do you know of any reputable source that uses dE the way you advocate here for grayscale measurements. Your silence indicates that no you do not.

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Originally Posted by Bear5k View Post

Tom - Please stop. Seriously. Reading comprehension is not your strong suit. I'm having fun picking this apart, but now you are embarrassing yourself.

So that we are clear: the method should be constant across any set of numbers. The output is what changes based upon the inputs. All that I posted, above, was a set of numbers that were straight CIE76 with dL = 0 and a constant du' and dv'. That's all. The point was to demonstrate a desirable property of color error that was intended by the CIE, and that also shows up in CIE94 and CIE00. It is this property that our little trick preserves, while eliminating gamma error. No, we do not aribtrarily set dL to 0.

The obnoxious hand waving aside, this is an important point that I want to emphasize. The quote you (thankfully) reproduce in full made 2 points. First, I mentioned the fact that Derek offered an irrelevant and misleading point about color perception at very low light levels as a way of justifying this methodology (a tactic you have had the good sense to not repeat). I only mentioned it because using this type of technical nonsense as a marketing tactic irritates me. Second, I wrote that "Nonetheless, you apparently continue to endorse the view that we should calculate the dE of a specified white, say x0.314, y0.351, differently at 90% stim than at 100% stim where our variable sensitivity to color perception is surely irrelevant." This was not phrased correctly. What I should have said was "Nonetheless, you apparently continue to endorse the view that we should calculate the dE of a specified white, say x0.314, y0.351, in such a way that at 90% stim you get different results than at 100% stim where our variable sensitivity to color perception is surely irrelevant."

Now here's a question for you and anyone else reading this. Given everything that has been written so far, what was more likely: a) that I was simply careless and misspoke; or b) that I truly didn't understand what you were doing?

Your natural inclination, of course, is to immediately respond based on b) because rather than argue the merits of this methodology, you insist upon simply attacking me. My understanding of CIE, my understanding of SMPTE, my understanding of your methods, etc. What's that old lawyer's adage? When the law is against you, argue the facts. When the facts are against you, argue the law. And when both are against you, attack your opponent.

There is nothing about this I don't understand. It is a simple point. The fact that you are not very enthusiastic about defending the methodology on its merits and resort instead to continually insisting that I lack understanding on this or that indicates the weakness of your position.

Here's CalMan's methodology (at least one of them) for calculating grayscale dE in the u'v' space. Assume a target gamma of 2.2, Rec. 709, and the following grayscale readings:
90% stim
x0.314
y0.351
Y0.793

20% stim
x0.314
y0.351
Y0.029

What's the dE? Well, using the method you endorse, the dE is 12.2 at 90% and at 4.1 at 20%. But, x0.314, y0.351 translates to
R 89%
G 105%
B 85%
and is an error large enough that it would be clearly visible at 20% stim and completely unacceptable as a calibration target. Yet, your dE metric says that the error is only 4.1, which is a (barely) acceptable result.

The formula is:
=SQRT((L1-L2)^2+(u1-u2)^2+(v1-v2)^2) where
L1=91.37 (@90%) 19.64(@20%)
L2=91.37 (@90%) 19.64(@20%)
u1= 0
u2= -8.392 (@90%), -1.803 (@20%)
v1= 0
v2= 13.64 (@90%) 2.93 (@20%)

This is a literal application of the CIE standard, and yet it gives an incorrect result: @ 20% x0.314, y0.351 is a good grayscale result. It isn't. A word to anyone else following this: If a calibrator tells you that this is an acceptable result, you should ask for your money back.

The correct implementation is the same formula, but with these values:
L1=100
L2=100
u1= 0
u2= -9.184
v1=0
v2= 14.92

for a dE of 17.5 regardless of the level of stimulus.

Bill, I understand what you are doing. That's the problem.

Quote:
Originally Posted by Bear5k View Post

The rest of this is simply demonstrating that despite having published a dE calculator of your own, you do not really understand what goes on in the numbers. Your complaint, in this case, is with the CIE itself, not us..

Yep. The numbers are what they are, it's not our method. In fact, it is a lot closer to yours. The only thing I did was let L* vary, rather than hold it constant to show how the CIE intended the equation to work. Obviously, you did not recognize that.

If you think it is as easy to see a given color difference when there is approx. 1/7th - 1/10th as much light around as what you are adapted to for white then that sounds like a testable hypothesis. One might even develop a model, of people's color perception. Here's a hint: if you want to be taken seriously, don't use your "sunlight/inside light" example from your WSR article. That one was simply bad.

This is just another repetition of what you have already said many times now. I invite anyone who cares to try to adjust their RGB biases to achieve x0.314, y0.351 @ 20% and see if you are able to clearly see the difference between that and x0.3127, y0.329 in test patterns and real program material.

Quote:
Originally Posted by Bear5k View Post

What consequences are there for practical application? That you set a high hurdle for imperceptibility? That you have to rely on software that does all of the computation for you in real time? That our users have to toggle a control if they want to use it? Do tell. I'm curious here, too.

As for common sense: I'm all ears. I'd really be entertained to learn why you prefer tool vendors who were fast-and-loose with published standards.

Again, I am not personally doing anything. Again, can you tell me of any other reputable source that uses the method you advocate for calculating dE for grayscale? Just one? Oh, yes, I already asked that question. I'm still waiting for an answer.

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Careful, you are perilously close to saying that SMPTE uses L* when computing dE (you would be right there, though individuals vary in interpretation as this thread demonstrates). However, your math is off. Let's leave aside Lab76 alone until we master Luv. In CIE76 or CIE94 terms, it is over 9.

That's odd, because you posted the number yourself as 18.4. But I guess that IS over 9. For the record, this is a REALLY minor point, but one you must emphasize as part of your "Tom doesn't understand" approach. The SMPTE standard is 4.0 Lab. That is roughly equivalent to 5.0 Luv. The dE of x0.314, y0.351 relative to Rec. 709 is 17.5 in CIELUV [dE(uv)] and 13.2 CIELAB in [dE(ab)].

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Agreed. However, your "simple experiments", judging by the WSR article, often involve such "minor nuisances" as significant changes in ambient light spectrum and luminous flux, so one does have to double-check these things.

You "agree" that the difference between 0.314, 0.351 and 0.3127, 0.329 at a typical 20% stim would be clearly visible and yet you continue to insist on a dE metric that reports the difference as perceptually negligible? OK, well that was easy. You just conceded the entire debate. BTW, is "ambient light spectrum and luminous flux" just a incredibly pretentious way of saying viewing conditions and perceived brightness? If you want to make a point here, you might want to fill that out a little.

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Huh? It does, and so does yours, unless you use dE(uv) for gamut work. We recommend people turn off gamma correction when doing primary/secondary work. This was discussed previously.

A given absolute difference in chromaticity would be less visible at lower light levels. Whether it drops below the threshold of visibility is another matter. This is curious from someone who just published something on the underappreciated nature of brightness in color measurement. Ironic, even.

You have basically 2 affirmative arguments for this methodology buried in the endless sniping at me: 1) it's the CIE standard; 2) people are less sensitive to color error at lower light levels so the dE number should reflect this. I was responding to 2), but on reflection I am not sure that this argument was sound. I withdraw it. BTW, this is the 3rd time you've referred to my WSR article. I'd be happy to comment on your published work in this area if you have any.

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Huh? Are you confusing white, which is a point, with gray, which is a line connecting white and black? If white changes, then the entire adaptation model changes (must be re-normalized). Luminous flux is captured in the "Lightness" component of color error. You really don't understand this, do you?

Whoa, are you actually insinuating that I don't understand something? Astonishing. You really need to try out some new material. No, Bill, I don't lack an understanding of white vs. gray.

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Gauntlet thrown; gauntlet accepted. I am now free to post my critique of your CMS document. Hilarity will ensue.

If this is typical of the level of discourse we can expect, I doubt that. You are, of course, free to post anything you like. It's a free country.

I'm not going to respond to your comments about Grassman's Law as I withdrew those comments in the next post, so it is a moot point.

Tom Huffman
ChromaPure Software/AccuPel Video Signal Generators
ISF/THX Calibrations
Springfield, MO

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post #34 of 37 Old 11-25-2009, 05:05 AM
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Resurrecting an old thread.

I am using Delta E 1976 for greyscale. And for colour, Delta E 1994.

In Calman the default is 1976. That is what I used when calibrating the grayscale.

However, where it gets confusing is the colour tab. In Calman there is a box in the middle labelled Delta E 94 (with the readouts for luminance, saturation, hue) already regardless of what is set in the global options. My formula preference in the Calman options are still set to 1976. Do I need to change this option, is Calman being clever and over-riding it for this screen tab anyway? I realised after calibrating and getting everything to less than a Delta E of 1, that I had not changed the global setting because I was reading the Delta E 94 box on the tab and assumed I didn't need to do anything!
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post #35 of 37 Old 11-28-2009, 08:33 AM
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Originally Posted by JonStatt View Post

Resurrecting an old thread.

I am using Delta E 1976 for greyscale. And for colour, Delta E 1994.

In Calman the default is 1976. That is what I used when calibrating the grayscale.

However, where it gets confusing is the colour tab. In Calman there is a box in the middle labelled Delta E 94 (with the readouts for luminance, saturation, hue) already regardless of what is set in the global options. My formula preference in the Calman options are still set to 1976. Do I need to change this option, is Calman being clever and over-riding it for this screen tab anyway? I realised after calibrating and getting everything to less than a Delta E of 1, that I had not changed the global setting because I was reading the Delta E 94 box on the tab and assumed I didn't need to do anything!

I thought this would have a quick answer. But as I didn't, I did the experiment myself. I can confirm that no matter what you set as the global option for Delta E measurement, for the Colour tab, it forces the display/use of 1994 anyway. The global setting does not affect the resultant reading.
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post #36 of 37 Old 11-29-2009, 07:46 PM
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Originally Posted by JonStatt View Post

I thought this would have a quick answer. But as I didn't, I did the experiment myself. I can confirm that no matter what you set as the global option for Delta E measurement, for the Colour tab, it forces the display/use of 1994 anyway. The global setting does not affect the resultant reading.

This actually depends upon the layout. You can set up the layout to use the global option or a specific set. The default-delivered layout uses some elements of dE94. Probably a better topic for the SpectraCal support forum, though.

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post #37 of 37 Old 11-30-2009, 12:51 AM
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Originally Posted by Bear5k View Post

This actually depends upon the layout. You can set up the layout to use the global option or a specific set. The default-delivered layout uses some elements of dE94. Probably a better topic for the SpectraCal support forum, though.

That makes absolute sense. Thank you. Understood about the Spectracal forum If I have further questions I will ask them there.
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