Post by michelb on Mar 27, 2017 7:16:58 GMT
My purpose is to show how the difference mode, which has not much interest in creative editing, can be used as a powerful tool to reveal hardly visible differences between two images.
It's also to show how it needs its companion tool: the gradient map adustment layer as a powerful 'magnifier'.
The pretext for the comparison will be to compare two versions of the same image, one in aRGB color mode, the other in sRGB.
I have deliberately chosen an aRGB original with cyan/blue shades that sRGB can't faithfully show.
Note: to get an aRGB mode, either you set the mode in your camera or you shoot raw. In the last case, you'll get an aRGB mode if the menu Edit >> color settings is set to 'always optimize for print'.
Now the workflow:
1 - open, then duplicate the image menu Image >> duplicate
2 - select the duplicate, and convert to sRGB, menu Image >> convert color profile
3 - select all (Crl A), copy (Ctrl C), select the original in the photobin, and paste as a new layer (Ctrl V)
You can switch the visibility of layers, and if your display permits, you'll see a color difference. With random original images, you would probably see no difference (no out of range colors).
4 - set the mode to difference: you'll better see WHERE there are differences. Once again, with random original images you would only see a black screen.
Now, it's time to use the black to white gradient map adustment layer magnifier.
You choose the black to white gradient (3rd one) and you move the white output slider tab to the left to get increased contrast. Moving it to 15 will be ok with that image, with random ones, you might have to move to 5 or even less.
Now you can see clearly the mapping of the differences.
This process can be applied to images where you suspect there may be 'out of range' colors in RGB. You'll find that beside cyan hues, there are others which sRGB does not reproduce faithfully.
It's also to show how it needs its companion tool: the gradient map adustment layer as a powerful 'magnifier'.
The pretext for the comparison will be to compare two versions of the same image, one in aRGB color mode, the other in sRGB.
I have deliberately chosen an aRGB original with cyan/blue shades that sRGB can't faithfully show.
Note: to get an aRGB mode, either you set the mode in your camera or you shoot raw. In the last case, you'll get an aRGB mode if the menu Edit >> color settings is set to 'always optimize for print'.
Now the workflow:
1 - open, then duplicate the image menu Image >> duplicate
2 - select the duplicate, and convert to sRGB, menu Image >> convert color profile
3 - select all (Crl A), copy (Ctrl C), select the original in the photobin, and paste as a new layer (Ctrl V)
You can switch the visibility of layers, and if your display permits, you'll see a color difference. With random original images, you would probably see no difference (no out of range colors).
4 - set the mode to difference: you'll better see WHERE there are differences. Once again, with random original images you would only see a black screen.
Now, it's time to use the black to white gradient map adustment layer magnifier.
You choose the black to white gradient (3rd one) and you move the white output slider tab to the left to get increased contrast. Moving it to 15 will be ok with that image, with random ones, you might have to move to 5 or even less.
Now you can see clearly the mapping of the differences.
This process can be applied to images where you suspect there may be 'out of range' colors in RGB. You'll find that beside cyan hues, there are others which sRGB does not reproduce faithfully.
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