Originally Posted by mahlerfan999
On the HCFR program under the preferences, there are advanced settings and one of them is to "use gamma reference to compute gray scale delta E" and if I set the reference to the actual average value that I found instead of 2.22 the software then uses the values based upon my actual gamma instead of the 2.22 reference. I can only imagine it having an impact for luminance values.
I also imagine that the gamma going so screwy at the low end makes the gray scale appear screwy if it uses the expected luminance values for white with a 2.22 reference gamma. I kind of take it as a "for your messed up gamma, you're actually tracking it well." But honestly I just don't know.
I think I can explain some of what you are seeing with the delta E calculation, which I have gleaned from reading lots of the threads and reproducing the HCFR numbers myself while working on my A650. For the grayscale/RGB measures, HCFR uses CIELUV76, which is a lot like the CIELAB76 measures
, except based on the value in the Luv space.
When you do not check the "use gamma reference to compute gray scale delta E" box, HCFR assumes a Y value of 1 for both the actual IRExx measure and the target measure. Thus, it removes luminance from the deltaE calculation, and the deltaE numbers give you a quantitative measure of whether the RGB balance matches white. You see the luminance affect only in the gamma graph.
Now let's take the case where the box is checked. If you look at the formulas for converting to the Luv space
, you will see that u and v are both multiplied by L. Effectively, then, at low luminance, the error measures for color are reduced proportionately and you see small deltaE values even when there is a large imbalance between red and blue.
The reality is that it is harder to see color differences at low luminance, the question is whether the CIELuv formulas overstate this when looking at grayscale. I have seen a discussion in one of the calibration threads where Tom Huffman took the position that one never wants to check this box, you need the deltaE to report to you when there is color shift. On the other side, a representative of the Calman folks argued that luminance should be included in the measure. As you noticed, you can have either high deltaE values or low deltaE values, without changing anything on the set. So each measure can be misleading in some sense. If you leave the box unchecked, you have to take into account that high deltaE values below IRE30 may be reporting color shifts that you cannot really see with your eyes, but at least low deltaE values would confirm that you are dead on. If you check the box, you have to take into account that low deltaE values may tell you everything is okay, when in fact there are significant, noticeable color shifts. Either way, many of the pros in the calibration thread say you have to use your eyes and the Pluge pattern to look for color shifts at the low luminance end.
None of this affects the reliability of your gamma chart, as gamma reflects just luminance and not the white balance.
Hope this helps,