Quote:
Harpmaker wrote:
 To put some hard numbers to the D65 vs C situation...
My Valspar flat enamel tinted Bermuda Beige. This is a pinkish-peach color to the eye.
"D65" L*a*b* values: 84.28, 6.36, 8.79
"C" L*a*b* values: 84.35, 5.82, 8.84
My Behr 1850 tinted Reference Gray (a very neutral dark gray).
"D65" L*a*b* values: 76.56, 0.01, 0.18
"C" L*a*b* values: 76.56, 0.05, 0.09   |
Good example Harp.
So what does all that mean? It's the same color but different numbers. That's because there are two different reference points used.
Now it can be clearly seen why when people talk about color in detail they must use the same reference. Even though the color is the same, if you convert those L*ab values to RGB to get a visual representation of what the color looks like, you will get two different RGB values, meaning two different colors, yet they are from the exact same source. So it really is important to make sure we are all talking the same language and using the same reference point or nothing can be compared.
If you know something was measured referencing a different Illiminant then it's easy to convert that to D65 and then to the RGB value.
Harp this also demonstrates what I said about a true neutral... notice how the neutral gray reference still meets neutral tolerance for both C and D65? (Although if you convert those values to RGB it may not look too neutral based solely on RGB numbers). The neutral reference values based on C come out to be 193 187 197 and based on D65 they are 189 189 189. Bermudia Beige 'C' - 234 204 203, D65- 229 206 194.
I think this does demonstrate very well how important it is to know what reference points are used when discussing colors. If we didn't know that the BB readings above were done in D65 and C, and say these were two different people reporting back... it would be very easy to say that one person got a bad batch when in reality they are perfectly fine. Even the neutral looks off with just the RGB numbers and might get passed over as a true neutral because two people are talking different references and don't know it. If someone showed me those numbers and included the L*ab values I would know right away what was going on, but others may not pick up on that and end up dismissing something when it is actually very good. I do know of one occasion when this exact thing happened, someone nailed a neutral with a mix by eye but because the RGB numbers were based on C, they abandoned that mix and went on to others, and none were as neutral as the one that ended up overlooked.
Like I said, it isn't wrong to use C, but to discuss the color balance everyone would have to be using the same reference, or know what was used and then convert to D65. Sometimes conversions can have user error and throw things off too, so me personally... I'll stick with D65, especially since it's the same language everyone in the film and video industry talk as well.
This is why I am such a stickler for correct data and not scanner or MS Paint values. We tend to throw a lot of things out on the table but unless there is a common reference, everything might as well be swept from the table to the trash because we can't discuss and compare colors unless we know exactly how the readings were done and what they were referenced to.