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Problem separating color from picture

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  #11  
Old 02-24-2010, 03:20 AM
ApWizard's Avatar
ApWizard ApWizard is offline
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Re: Problem separating color from picture

Well the Linear Light method produce some incongruence while recomposing so we have to work in 16bit mode with Apply Image:

• create a new layer, fill with white, change blending mode to color;
• merge all in a new layer, duplicate this and delete the white one;
• Apply Image on the second duplicate:
- layer: the color image one;
- invert: checked;
- blending: Add;
- scale: 2;
- offset: 0;

• invert the layer (CTRL+i);
• change the blend mode to linear light;

the Linear Light-colors-only layer stay over the black and white one.

Attachments:
1) color image;
2a) black and white layers done with a white layer in color mode (color contrast is visible)
2b) black and white using desaturation (no color contrast), that's the wrong way;
3) second copy of b/w layer after Apply Image and inversion;

actually there is no difference between the original image and the recomposed one. Just merge all and put in Difference blending mode over the original one, the result is a pure black (0000000) stating there is no difference at all
Attached Images
File Type: jpg 01.jpg (36.3 KB, 11 views)
File Type: jpg 02A.jpg (25.6 KB, 8 views)
File Type: jpg 02B.jpg (24.9 KB, 8 views)
File Type: jpg 03.jpg (11.6 KB, 11 views)
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  #12  
Old 02-24-2010, 03:39 AM
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Re: Problem separating color from picture

I think, I did it exactly as you described first and it basicly worked. But if I mix the images together there is a slightly shifted contrast to the original...

Oh wait, you posted just a new message. I will try that now...

Good hint with the 16 bit mode! I am relatively new to Photoshop, so I have to learn alot...
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  #13  
Old 02-24-2010, 04:25 AM
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Der_W Der_W is offline
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Re: Problem separating color from picture

I always used to create a duplicate of the background layer, set its mode to "Color" and fill the background layer with a 50% gray (or any shade of gray, that's just my standard fill entry ;-)).
After that go to "Edit"-"Fade" and fade it to "Hue" mode.
Works great for me (and using yet another copy of the background layer on top in "Difference" mode tells me that there's no difference between the original and the color separated image.

I uploaded you an action that does exactly that if you didn't understand everything I explained :-)
Attached Files
File Type: zip Separate DerW.zip (496 Bytes, 10 views)
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  #14  
Old 02-24-2010, 05:59 AM
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Re: Problem separating color from picture

That's actually a drastically simplified version of the first one and it does not produce any difference in contrast like the stuff above (without "Apply Image").
Much faster too.

Really great!!!

But the problem with all those techniques is that the color is placed on that grey background. I think it's actually limiting creativity.
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  #15  
Old 02-24-2010, 06:11 AM
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Re: Problem separating color from picture

Is there a way to generate alphatransparent images from the gray color pichture?
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  #16  
Old 02-24-2010, 06:16 AM
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Re: Problem separating color from picture

Quote:
Originally Posted by _jason_ View Post
That's actually a drastically simplified version of the first one and it does not produce any difference in contrast like the stuff above (without "Apply Image").
Much faster too.

Really great!!!

But the problem with all those techniques is that the color is placed on that grey background. I think it's actually limiting creativity.
I think that is mathematically correct. If you have some white in the image, or black or gray, there is basically no color information and that's expressed by 50% gray.
Linear Light in the recomposition (or the others blending modes used by Der_W in the simplified working version) ignore that 50% gray.
As far as you don't touch the luminosity it works fine.
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  #17  
Old 02-24-2010, 09:40 AM
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Re: Problem separating color from picture

I think I'll take a look at the plugin SDK.
I need the separation in another way as it is done with the techniques above.

I really need accurate separations of the greyscale and the color channels as alphatransparent images. Also (optionally) red, green, blue separations on alphatransparency.

The parts have to give 100 percent accurate result if merged back on a white background (no blending modes used at all then).

I know there is a plugin called "Tinter" or so, which does just similar things (recoloring images by separating color information and re-applying modifications to the generated greyscale images). Surely worth to take a look at that too...

Thanks for all the help!

Jason
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