- Wed Jun 11, 2008 6:28 pm
#272262
If you're making/editing your greyscale textures in Adobe Photoshop,
you should read this post carefully. Because it's extremely vital for having
precise goals.
By default -literally for press purposes-, Photoshop has "Dot Gain 20%"
profile for greyscale images. This is a setting for compensating the black ink
diffusion over paper for avoiding dark output when printed. You may wonder
how much this could be affecting your 3D world. Well, too much!
For example, you want 50 percent grey texture for some purpose, what'd you do?
1) Load Photoshop, open a new greyscale document
2) Pick color 127,127,127 and paint with it
Right? Well, I think "yes"...
And you'd probably verify the color from info by reading 127,127,127
Or you'd do these on an RGB document and convert it to greyscale in the end.
Save it? Right? Yes...
You now have an incorrect map because Photoshop applied Dot Gain 20% profile.
Open your map again, oh it's still 127,127,127 so what's wrong here?!
No, it is NOT. Because Photoshop just simulates the same profile now.
As a horrible fact it saved these pixels as 104,104,104!
You don't believe? Open the image in another imaging application and verify.
Of course it's essential that application should have color management
turned off before testing this. Or better, pick one without color management.
So, what's bad about it?
For example you need a weight map and you need precise grey tones,
like you need 50% grey and 10%, too, etc. But painting with 127 won't
give you desired output if you're working in Photoshop just because of
this hidden fact and maybe you'd never know what's happening.
Here's a result from my displacement test which failed due to this:
The bars had to be at 20%, 50% and 100% as I've painted them with
Grey 51, Grey 127, Grey 255. Although with Photoshop defaults
Now, here's the same test with an RGB texture using colors 51,51,51
127,127,127 and 255,255,255 which is precisely same as above texture.
Yes, this was the correct expected look also with the above grey texture
but it didn't give the same result as RGB one. Who was responsible?
Of course, Photoshop's press purpose defaults!
So, how should you set Photoshop for CG purposes?
1) Go to Edit / Color Settings
2) Click "More Options" button
3) Find "Gray" profile having "Dot Gain 20%" in front of it
4) Change it to "sGray" and you're done!
If for some reason you don't have it listed, load it:
sGray.icc
Download >>> http://www.divshare.com/download/2525027-ed7
Now, you can make correct greyscale textures in Photoshop!
If you also need to use press defaults grey profile frequently, you can
stay at Dot Gain 20% and avoid this problem by doing the following:
* On new document, make sure you select sGray before to start:
* Or if you've already opened a greyscale image (or converted it from RGB),
you can still convert is to sGray profile from Edit / Convert to profile...
Although conversion is lossy and you may want to deselect dithering
if you're dealing with flat grey areas on your image.
As a final word, for example you didn't know all of the above and
you've find and loaded a grey RGB image into Photoshop and
decided to convert it to Greyscale because it was already grey.
Oh, now that image is not the same image anymore
you should read this post carefully. Because it's extremely vital for having
precise goals.
By default -literally for press purposes-, Photoshop has "Dot Gain 20%"
profile for greyscale images. This is a setting for compensating the black ink
diffusion over paper for avoiding dark output when printed. You may wonder
how much this could be affecting your 3D world. Well, too much!
For example, you want 50 percent grey texture for some purpose, what'd you do?
1) Load Photoshop, open a new greyscale document
2) Pick color 127,127,127 and paint with it
Right? Well, I think "yes"...
And you'd probably verify the color from info by reading 127,127,127
Or you'd do these on an RGB document and convert it to greyscale in the end.
Save it? Right? Yes...
You now have an incorrect map because Photoshop applied Dot Gain 20% profile.
Open your map again, oh it's still 127,127,127 so what's wrong here?!
No, it is NOT. Because Photoshop just simulates the same profile now.
As a horrible fact it saved these pixels as 104,104,104!
You don't believe? Open the image in another imaging application and verify.
Of course it's essential that application should have color management
turned off before testing this. Or better, pick one without color management.
So, what's bad about it?
For example you need a weight map and you need precise grey tones,
like you need 50% grey and 10%, too, etc. But painting with 127 won't
give you desired output if you're working in Photoshop just because of
this hidden fact and maybe you'd never know what's happening.
Here's a result from my displacement test which failed due to this:
The bars had to be at 20%, 50% and 100% as I've painted them with
Grey 51, Grey 127, Grey 255. Although with Photoshop defaults
Now, here's the same test with an RGB texture using colors 51,51,51
127,127,127 and 255,255,255 which is precisely same as above texture.
Yes, this was the correct expected look also with the above grey texture
but it didn't give the same result as RGB one. Who was responsible?
Of course, Photoshop's press purpose defaults!
So, how should you set Photoshop for CG purposes?
1) Go to Edit / Color Settings
2) Click "More Options" button
3) Find "Gray" profile having "Dot Gain 20%" in front of it
4) Change it to "sGray" and you're done!
If for some reason you don't have it listed, load it:
sGray.icc
Download >>> http://www.divshare.com/download/2525027-ed7
Now, you can make correct greyscale textures in Photoshop!
If you also need to use press defaults grey profile frequently, you can
stay at Dot Gain 20% and avoid this problem by doing the following:
* On new document, make sure you select sGray before to start:
* Or if you've already opened a greyscale image (or converted it from RGB),
you can still convert is to sGray profile from Edit / Convert to profile...
Although conversion is lossy and you may want to deselect dithering
if you're dealing with flat grey areas on your image.
As a final word, for example you didn't know all of the above and
you've find and loaded a grey RGB image into Photoshop and
decided to convert it to Greyscale because it was already grey.
Oh, now that image is not the same image anymore
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