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Photoshop's 50% gray

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  #11  
Old 02-24-2015, 05:38 PM
A Grade A Grade is offline
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Re: Photoshop's 50% gray

The scale does start at 0, so once you've done 256 / 2 = 128 don't you have minus the 1 making it 127 so it fits back into the 0 to 255 scale?
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  #12  
Old 02-24-2015, 06:20 PM
klev klev is offline
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Re: Photoshop's 50% gray

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Originally Posted by A Grade View Post
The scale does start at 0, so once you've done 256 / 2 = 128 don't you have minus the 1 making it 127 so it fits back into the 0 to 255 scale?
What do you mean? You have an even number of bits, so you lack a specific middle level. They have to designate one as invariant for that blending mode, and it was determined to be 128. If you used either 257 or 255 total levels, you would have a distinct middle value, not that it really matters. You lose more precision to other things.
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Old 02-25-2015, 12:00 PM
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andrewrodney andrewrodney is offline
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Re: Photoshop's 50% gray

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Originally Posted by mcdronkz View Post
Is 50% gray really 50% gray? It looks different using different color profiles.
Sure does. Just make a few documents in different color spaces and examine RGB values when you set Lstar to 50 (which really is middle gray). Otherwise, 128 is just a number that's halfway between the two extremes (0-255). RGB numbers don't tell us what a color looks like, they are a partial ingredient and we need an assigned color space to tell us what's what. Lab where Lstar is 50 is a different story. That does define middle gray as we would see it. John is correct:
- 50% gray in PS just means the mathematical halfway point which is 128
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