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Historically, grayscale work used dE 76 and color stuff used dE 94.
It is still taught that way. although like gamma used to be, it also depended a lot on which expert you were talking to.
Regards
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Michael Chen @ The Laser Video Experience
ISF/THX/TLV Video Instructor
The Video Calibration Education Hub  www.TLVEXP.com
and de94 for gamut as Michael posted...
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CalMANv5 will use dE2000 by default for everything because it's more uniform (for color errors) than the older formulas.
Every time a "newer" method of calculating perceptual errors comes out, it is touted as being "better" but every time, it doesn't take too long for someone to find flaws in the newer method. To this day, there's not a single color space option that is perfect/accurate/reliable for every possible measurement.
uv/uvL space relies on hue, saturation, and Luminance to define colors (and to calculate errors). It's difficult, but not impossible, to encounter perceptual errors in uvL space BUT... uvL has the advantage of behaving most like human visual perception in most circumstances. You can think of uvL space as a cylinder with dark (black) on the end of one axis, white at the other end of the center axis, saturation running radially from the center axis to the outside, and hue running around radially. It avoids all sorts of nonlinear functions that have to be applied to other spaces to get the "other" dEs (1994, 2000, etc.).
So if you want to be thorough, use dEuv PLUS an additional calculation of your choice... I use 1994, you may want to use something else.
uv (and uvL) is still probably the most perceptually "reasonable" color space, so using dEuv makes a lot of sense. I use dEuv for both grayscale and color. But I also use dE94 (as an additional line of data in the "raw data" table in CalMAN) as a sanity check to avoid large errors that are missed by the dEuv calculations.
Every time a "newer" method of calculating perceptual errors comes out, it is touted as being "better" but every time, it doesn't take too long for someone to find flaws in the newer method. To this day, there's not a single color space option that is perfect/accurate/reliable for every possible measurement.
uv/uvL space relies on hue, saturation, and Luminance to define colors (and to calculate errors). It's difficult, but not impossible, to encounter perceptual errors in uvL space BUT... uvL has the advantage of behaving most like human visual perception in most circumstances. You can think of uvL space as a cylinder with dark (black) on the end of one axis, white at the other end of the center axis, saturation running radially from the center axis to the outside, and hue running around radially. It avoids all sorts of nonlinear functions that have to be applied to other spaces to get the "other" dEs (1994, 2000, etc.).
So if you want to be thorough, use dEuv PLUS an additional calculation of your choice... I use 1994, you may want to use something else.
CalMANv5 will also support dELuv in addition to the current dEuv.
The Luv color space offers a few advantages for grading video performance. First, it offers a linear chromaticity chart, which Lab does not. This factor was decisive in CIE approving Luv as a Lab alternative in 1976. Second, it is somewhat more sensitive than Lab to small errors in gray, so it presumably offers a little more granularity. Third, it weights red errors somewhat more than Lab, which can be important for getting skin tones correct.
However, the 1976 (Lab or Luv) formulas have some rather profound shortcomings regarding their treatment of luminance errors in color. Thus, I would only use CIELUV for grayscale analysis. For color, use CIE94 or CIEDE2000.
Tom Huffman
ChromaPure Software/AccuPel Video Signal Generators
ISF/THX Calibrations
Springfield, MO
CIE u'v' which is a more uniform 2D colorspace similar to xy.
and
CIE L*U*V* which is very similar to CIE L*a*b* .
The dE uv in CalMAN uses the CIE u'v' space so it is only chromaticity that is reported as error with no regard to luminance or perception.
SpectraCal
CalMAN Lead Developer
One thing to note is that there are two types of uv.
CIE u'v' which is a more uniform 2D colorspace similar to xy.
and
CIE L*U*V* which is very similar to CIE L*a*b* .
The dE uv in CalMAN uses the CIE u'v' space so it is only chromaticity that is reported as error with no regard to luminance or perception.
but v5 should have that latter as well? (L*U*V*)
One thing to note is that there are two types of uv.
CIE u'v' which is a more uniform 2D colorspace similar to xy.
and
CIE L*U*V* which is very similar to CIE L*a*b* .
The dE uv in CalMAN uses the CIE u'v' space so it is only chromaticity that is reported as error with no regard to luminance or perception.
You would never use u'v' for color. It's value lies in grayscale analysis only, where the luminance performance is better treated as gamma response. For the reasons I mention above, I would also not recommend using CIELUV (or CIELAB) for color either, though this is merely a suboptimal idea as opposed to using u'v', which would be a terrible idea.
BTW, the subject of the various color difference formula and their relative performance is a subject that I find endlessly interesting, and strongly influenced by decision to get into this field. CIE endorsed a new color space CIECAM02, but has not yet settled on a color difference formula that uses it. You can find several examples on the web showing how this might be done.
Tom Huffman
ChromaPure Software/AccuPel Video Signal Generators
ISF/THX Calibrations
Springfield, MO
CIE u'v' is a coordinate system where every chromaticity has a fixed value, d65 = 0.1978, 0.4683 u',v'
CIE L*U*V* is based on a white point, so the reference point for white is 0,0.
But if the white point is D50, the u'v' coordinates shift to 0.2092,0.4881, while L*U*V* is still 0,0 since it's coordinate system is in reference to white.
One is a competitor to L*a*b*, where you actually get perceptual saturation effects, and u'v' is the replacement for x,y where you are simply describing chromaticity without respect to perceptual saturation.
The saturation of colors based on luminance is very significant as well.
For Red the u'v' targets are always 0.4507, 0.5229
In L*U*V* at 100% they are 53.2, 175.01, 37.75
at 30% they are 12.7, 41.85, 9.02
So as drop in target luminance the ability to perceive saturation drops as well
SpectraCal
CalMAN Lead Developer
I believe this is the root of most of the misunderstanding.
CIE u'v' is a coordinate system where every chromaticity has a fixed value, d65 = 0.1978, 0.4683 u',v'
CIE L*U*V* is based on a white point, so the reference point for white is 0,0.
But if the white point is D50, the u'v' coordinates shift to 0.2092,0.4881, while L*U*V* is still 0,0 since it's coordinate system is in reference to white.
One is a competitor to L*a*b*, where you actually get perceptual saturation effects, and u'v' is the replacement for x,y where you are simply describing chromaticity without respect to perceptual saturation.
The saturation of colors based on luminance is very significant as well.
For Red the u'v' targets are always 0.4507, 0.5229
In L*U*V* at 100% they are 53.2, 175.01, 37.75
at 30% they are 12.7, 41.85, 9.02
So as drop in target luminance the ability to perceive saturation drops as well
=SQRT((100100)^2+(0.0  5.705)^2+(0.0  1.216)^2)
Are you suggesting using the u'v' coordinates u'0.1948, v'0.4683 and u'0.2022, v'0.4963 instead?
Tom Huffman
ChromaPure Software/AccuPel Video Signal Generators
ISF/THX Calibrations
Springfield, MO
CIELUV is now 35 years old. There has been an enormous amount of research by color scientists since 1976. Since 76 the dE formulas have become increasingly complicated in an effort to address shortcomings discovered with the earlier formulas. All of the dE methods approved by CIE since 1976 have been based on the Lab color space.
The Luv color space offers a few advantages for grading video performance. First, it offers a linear chromaticity chart, which Lab does not. This factor was decisive in CIE approving Luv as a Lab alternative in 1976. Second, it is somewhat more sensitive than Lab to small errors in gray, so it presumably offers a little more granularity. Third, it weights red errors somewhat more than Lab, which can be important for getting skin tones correct.
However, the 1976 (Lab or Luv) formulas have some rather profound shortcomings regarding their treatment of luminance errors in color. Thus, I would only use CIELUV for grayscale analysis. For color, use CIE94 or CIEDE2000.
I've always found it odd that calibrators haven't embraced the progress made over the last 35 years. Why wouldn't one simply use CIEDE2000? To not do so suggests that CIE development has headed off in the wrong direction.
And that's why it's the default dE formula in CalMAN5.
Of course we make it easy to switch formulas if you have a personal preference.
SpectraCal
CalMAN Lead Developer
how different are dE1994 and dE2000 for gamut? for grayscale?
Tom Huffman
ChromaPure Software/AccuPel Video Signal Generators
ISF/THX Calibrations
Springfield, MO
Tom Huffman
ChromaPure Software/AccuPel Video Signal Generators
ISF/THX Calibrations
Springfield, MO
I mostly agree, especially with respect to the odd attraction to CIELUV. I am reluctant to wholeheartedly endorse CIEDE2000 I guess for philosophical reasons. I am skeptical that the very small difference in uniformity is worth the truly immense increase in complexity. The complete CIEDE2000 formula is almost comically complex.
does the complexity issue affect the end user at all or just the software developers?
I guess my main question would be less in relation to the complexity of the calculation, but rather given a particular dE2000 result whether the hunt for a better result is made more complex (if that makes sense)...
And I wouldn't say that programming dE 2000 is that complex. If I can manage it in an Excel spreadsheet, a programmer will find it a breeze. CIECAM02 looks like a different kettle of fish...although perhaps the dE formulation ends up being easier, I have no idea.
I guess my main question would be less in relation to the complexity of the calculation, but rather given a particular dE2000 result whether the hunt for a better result is made more complex (if that makes sense)...
dE 1976
dE 1994
where,
dE2000
where,
Here's the added performance of each successive formula
As I said, my only point was philosophical. With CIE94, you get a large increase in performance for a modest increase in complexity. With CIEDE2000 you get a small increase in performance with a huge increase in complexity. CIECAM02 seems to offer little over CIEDE2000, which is why I suspect that it has not been formally adopted. For the user, this added complexity means nothing. Even for the developer, once it is in place all the work is done.
I just have an affinity for Ockham's Razor.
Tom Huffman
ChromaPure Software/AccuPel Video Signal Generators
ISF/THX Calibrations
Springfield, MO
https://dl.dropbox.com/u/70685392/deltaE%282000%29%202.xls
CIELUV : white (4.0), color (4.0)
CIELAB : white (3.0), color (3.0)
CIE94 : white (3.0), color (1.5)
CIE2000 : white (3.0), color (1.5)
it would honestly be great if threads like this were not turned into a 'measuring of swords'.
Those of us that know enough to be capable also know that while the fundamentals are, more or less, in place there are so many varied 'professional' opinions that the term science often fades from view.
Jason
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uv (and uvL) are REALLY all you need if you are using calibration measurements and you are using the calibration software to display an appropriate luminance graph so you can see if there's a possibly understated Luminance error... it will be right there in the software's graph. Most of the differences in 1931 vs 1972 vs 1994 vs 2000 fix oddball "miscalculations" in unusual colors and aren't necessarily focused on making red, green, blue, cyan, magenta, and yellow calculations particularly better... though they do tend to improve.
Someone mentioned calibrators not taking advantage of "newer developments" or "newer science"... if we were working with some esoteric colors that had historic problems being measured accurately... certainly, some "newer science" might be worthwhile. But we're measuring white (and gray) and 6 other highly defined colors that are the 6 colors ANY error calculation method has to get reasonably right in order to not be laughed out of existence.
In short, if you know what you are doing and you use the calibration software correctly (so you can see how close your measured points are to the reference coordinated and so you can see how accurate (or inaccurate) your luminance values are, you really don't even NEED and error calculation unless you simply need to know if +1 green produces a higher or lower error than +2 green (for example). You could achieve the same end calibration result just by zoomingin on the reference point so you see your measurement and the reference with more resolution. In fact, if the cal software supports that capability, I'd venture to say a good calibrator could produce essentially "perfect" results for a given display without a single dE calculation as a guide (by "perfect" I mean get the display as accurate as it can be made given the controls, brand, and model).
With out a doubt that is true. dE's are good to let you know when it doesn't matter any more, but finding optimal settings doesn't require dE at all.
SpectraCal
CalMAN Lead Developer
uv (and uvL) are REALLY all you need if you are using calibration measurements and you are using the calibration software to display an appropriate luminance graph so you can see if there's a possibly understated Luminance error... it will be right there in the software's graph.
Someone mentioned calibrators not taking advantage of "newer developments" or "newer science"... if we were working with some esoteric colors that had historic problems being measured accurately... certainly, some "newer science" might be worthwhile. But we're measuring white (and gray) and 6 other highly defined colors that are the 6 colors ANY error calculation method has to get reasonably right in order to not be laughed out of existence.
Also, the Labbased formulas and Luv weight the contributions of RGB error differently, so if there is a residual error (you can't get it perfect) it is useful to have a dE number to tell you whether that error meets reasonable tolerances. Obviously, because the formulas weight the RGB contributions differently, you may get different results depending on the dE formula you use.
Of course, if you get a really low dE value when you are finished, then it doesn't matter which formula you use. A dE of 1 is going to be a very accurate color regardless of the dE method used to calculate it. It is when the result is less than perfect and compromises have to be made where these sorts of decisions make a real difference.
Tom Huffman
ChromaPure Software/AccuPel Video Signal Generators
ISF/THX Calibrations
Springfield, MO
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