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# Posts by hwjohn

Tom, Is the original method incorrect you proposed incorrect? I guess I'm a little confused as to why gamma shows up in the second calculation but not the first?
Tom, can you use your spreadsheet to calculate the xyY with gamma = 1? I wonder if that will yield our linear calculation results... which may be a clue.
I don't know at this point Dan. I have a feeling gamma corection has something to do with it, and that is why you see a non-linearity. Tom just posted some good info that we can experiment with.
Dan, Tom's Accupel and Bruce Lindblooms calculator both suggest the following targets for Red: 75% x0.574, y0.330 50% x0.456, y0.329 25% x0.366, y0.329 You can check out Lindblooms calculator on his site. If you input 1, 0.5, 0.5 (which is what Tom is using with his Accupel) in the RGB box (leave scale unchecked) then you will get the 50% value above. Likewise, if you take the 190, 95, 95 RGB triplet used to master AVSHD 50% Red Sat pattern and normalize it...
Well now we've done it. See what happens when you speak of that which we do not speak of? HINT: This thread isn't meant for discussion of what an IRE/volt/digital value is or the magical powers such entity may or may not possess.
Dan, Check your calculated targets against the targets Tom posted in post 17. I believe they are different. We are trying to figure out why. Bruce Lindbloom's calculator gives those xy as the correct targets for Red.
I think the issue that Dan brought up is probably the reason the HCFR guys chose to keep it constant. I'm sure they knew exactly what the xy targets should be and how to get the correct RGB, so holding Y constant for them may have been trivial. At this point I'm stumped on the xy coordinates. It seems from the HCFR help file that we are doing the same thing that they are. I feel fairly sure that the different methods we are using (Lindbloom/Accupel/Our calcs) are all...
I don't either. Are you going to find out for us?
Tom, I just tried normalizing the 50% red we are using (190,95,95) and put those numbers into Lindblooms calculator. Basically use 190/219 for R, and 95/219 for Green and Blue (Scale box unchecked). The resultant xyY is much closer to the Accupel/Lindbloom numbers you give, indicating that (190,95,95) may actually be a correct triplet for 50% red sat. It appears that all of us may be calculating the target x,y incorrectly. I was doing it the same way you were, by...
I'm pretty sure that Lindbloom (who I also played around with) uses PC levels. Maybe I'm thinking about it wrong, but 100,50,50 is different for PC level 0-255 than video level 16-235. In other words, when you use Lindbloom's calculator, you are getting an x,y output based on 0-255. Maybe I'm crazy. At this point I have looked at it too long and need to take a break. EDIT: Nevermind, just saw you can use it with normalized 0-1. I got the same xy you got with 1, .5, .5...
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