Quote:
Originally Posted by

**HDTVChallenged**
You can choose to calculate dE based solely in two dimensional space (x,y) or three dimensional space (x,y,Y). The latter option effectively "weights" the calculation so that rather large (x,y) errors are masked by the much smaller differences in Y (from the target point.)

**I've seen (x,y) dE errors of 86 or more at 10% stimulus drop to 6-9 (ish) once Y is taken into account.** .

There is ZERO "weighting" of dE by including or excluding luminance from the calculation. You are simply doing two entirely different calculations. Since there is NO luminance included when you use xy or uv or any 2 other coordinates, there's no "weighting" when you add luminance.... you simply add luminance to the calculation. Much like air speed vs land speed.... air speed includes the effects of headwinds or tail winds - this is not "weighting" either, it's simply 2 different ways of measuring speed -- each has it's purposes... as do dE calculations with or without luminance included.

Quote:
Originally Posted by

**HDTVChallenged**
Whether large (x,y) errors at low luminance levels are really worth "sweating over" is another discussion.

One of the things that has improved to some extent with each newer method of calculating dE actually involves "weighting" to make some errors that had small error values in prior calculation methods but were fairly easy to see, es[ecially in side-by-side comparisons. In this case "weighting" does apply because newer formulas try to avoid missing or understating some errors so that ALL errors are equally represented. We still not quite there yet, but dE calculations, in general, are getting better with each new generation of adopted calculation methods. This is ENTIRELY different than using or not using luminance in the calculation. The changes in dE formulas attempt to make a error in, say, salmon pink/orange have the same dE number as an equivalent error (equivalent in how visible the error is) in, say, green, or red, or some other common color.

Quote:
Originally Posted by

**HDTVChallenged**
As always, YMMV, which is why it's nice to have the option to choose between the two methods.

Uhhhhh, YMMV doesn't apply to dE calculations. You can use 1, 2 or 3 coordinates in the calculation. If 2 people measure the same coordinates and both perform the SAME dE calculation using the same number of coordinates, their calculations will NOT vary... they will be the same. Which is the whole point of dE. As long as you are making accurate measurements, and using the formulas correctly and are using the same coordinates (usually 2 or 3 coordinates), you will always get the same result. Software like CalMAN allows you to select the coordinates you use for your dE calculations... as long as whoever you are talking to or comparing notes with is using the same coordinates and the same dE method of calculation (i.e. 1931, 1972, 1994, 2000, etc.) you will be making valid comparisons. (this of course assumes the software doesn't have a bug in dE calculations as CalMAN apparently did for some period of time).

Quote:
Originally Posted by

**HDTVChallenged**
PS: To be honest, I don't really pay any attention to dE until after I'm done "twisting the knobs." I don't find it all that useful from a "mechanical" viewpoint.

Well, you SHOULD be paying attention to dE as you go along... using it as a sanity check can save a TON of time. I look at 3 dEs (usually 1931, uv, and 2000) as I make measurements because graphs don't always tell you how visible an error is, but dE WILL tell you that. I use 2 coordinates plus a 3rd graph with enough "resolution" (fixed vertical axis so as not to be fooled by the software adjusting the axis to make a large error appear small). The setup of the 3rd graph (for luminance) is critical though. There have even been times when I will use xy and xyY dE calculations or uv and uvL so I can see the effects of luminance errors EASILY -- and that's one of the major advantages of a flexible software program like CalMAN. A raw data table can be setup to show you dEuv in one row and you can then have CalMAN display dEuvL on the very next line. uvL color space is pretty useful for calibration since you are looking at one of the more perceptually accurate color spaces because the coordinates are hue, saturation, and Luminance which also happen to be the controls in video displays that have CMS controls. And dEuvL doesn't change periodically while the formulas for calculating dE1931, 1972, 1994, 2000, etc. each have their own unique formulas that attempt to treat all errors equally... with the newer versions getting closer... but none of them are "perfect" yet. Which is why you want to look at more than one dE calculation while you are calibrating. I find myself trying to make the errors for all the dE calculations I look at less than 3 with luminance errors as small as I can get them. You can't always make 2 or 3 or 4 dE calculations all come out lower than 3, but many times you CAN get a better calibration by looking at multiple dE calculations.