Thanks for the typo on peak white, I've corrected this in my post.
As I said, 100nits is a legacy reference white value. It is still used by colorists when they grade for HDR because it makes their SDR grade easier. I am sure there are 100nits manual patterns floating around for this reason. But it's not part of the standard. I'm sure that Light Illusion would mention it for simplicity, as a shortcut, but it wouldn't be the first time they are not 100% correct regarding standards. It took them a while to implement BT1886 properly.
I have stopped using manual patterns for calibration about a decade ago, so I'm not going back there when calibrating.
I really don't mind which value you choose. I was only pointing out that AFAIK
, there is no reference white defined in the standard, and that the closest value used in a standard calibration layout was 94.378nits, which it 50% white according to Calman.
This is the value that most professional calibrators not using manual patterns but using an automatic pattern generator will use. It's up to you to decide whether you want to use a legacy value for this (100nits), which calibrators won't be able to measure easily using a pattern generator (100% of pro and most enthusiasts do it that way), or if you prefer to use a value which means something in PQ terms, i.e. 50% white and is therefore measured during an HDR calibration. If Calman's value of 94.378nits is wrong, I'll report it and they'll correct it, so let's not argue about the actual number if you believe it's wrong. What's important is for you to make a decision regarding which "reference white" it is more useful to have in your software, a legacy value that doesn't have any corresponding pattern in a professional (and enthusiast) calibration layout, or a value that is measured in every greyscale sweep when using automatic pattern generators, whether it's done in 11 or 21steps (the most commonly used increments).
Understood, that's what I thought. It just seems to me that just as you add soft start and hard clip points to the plot (outside of the normal spacing) so we can clearly see where they end, you could do the same for "reference white" as it looks like you'd have the space to do this around the area used by this random 48nits value.
You don't have to start from x, you can start from the value you have for y, just like for the two other values. It doesn't matter at all if it says exactly 94.378nits on x (assuming this is the correct value for 50% white) or something slightly different. It's just a useful value (whether you choose to go with 100 or 94nits) to have on the plot, so we can see easily what's before and after "reference white" on the curve. You don't show the exact value input for hard clip either on x, and it doesn't matter, it shows where we hard clip on the plot, and that's useful.
Just to clarify, I'm fine with no values at all on the plot, your tool is great as it is for me, I'm only trying to help making it more useful to others. So don't waste any time doing anything for me. I make suggestions, if you like them, take them, if you don't, leave them and spend the time on more important stuff
Keep up the good work!