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Colour alterations thru deleting channels


Faouaz Alyagout

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Hi,
I am very fond of Colour alterations on a photo through manipulating RGB or CMYK channels. I recently stumbled upon a method that gave a rather very interesting colour effect I think. I deleted the blue channel out of my RGB image, that left me with cyan and magenta channels. However the problem is that I cannot save that image with the usual formats such as PNG and JPEG. I can only save it as PSD and a bunch of other technical formats. I suppose it is because a channel is missing. I have tried to fill the blue channel with black but that did not give the same effect. Is there a way to save the image with that colour effect, or somehow achieving the exact same result through a method without deleting a channel?
I'd really appreciate your help. Merry Christmas and happy new year.
Screen Shot 2014-12-27 at 10.58.08.pngScreen Shot 2014-12-27 at 10.58.17.pngScreen Shot 2014-12-27 at 10.58.58.png
 

Tom Mann

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FWIW, you can get quite similar color efx by the following procedure:

1. Click on the blue channel - this will select it and turn the other channels off.

2. Click on the "eye" for the main, RGB channel - this will turn on all the other channels, but not select them.

3. Go to image/adjustments/levels, and move the left slider of "output levels" to about 128, and hit "OK".

This will produce colors nearly the same as what you see on screen if you delete the blue channel (as you described in your post), but with this method, the result will be able to be saved by normal methods, not just screen shots.

Using the other sliders, or using the "curves" tool, you can further tune the colors to get the look you want.

HTH,

Tom M
 

IamSam

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A Channel mixer adjustment layer will allow you to do the same thing. In the mixer, just select the channel (blue) and adjust the sliders.
 

IamSam

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You can also use the Advanced Blending in a layer style to turn off the blue channel.

Screen Shot 2014-12-27 at 8.26.23 AM.png

The Channel Mixer adj layer provides a bit more adjustability.
 

Tom Mann

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To me, the more interesting and deeper question is why Adobe software engineers decided to make the result of deleting a channel different from simply replacing a channel with all black or all white, or all gray, or something simple like that. :eek:. They probably have/had something in mind, but whatever it is, it's not obvious to me.

Another question is why did they essentially set up a rule that unless one has all three channels present, you can't save the result in the usual way (ie, the whole point of this thread). Perhaps they didn't want people inadvertently saving images that were missing a channel, but IMHO, they could have just as easily provided one of the usual, "are you sure you want to do tthis" types of warnings.

If anyone has some insight into these two design decisions, I would love to hear it.

Regards,

Tom M
 

thebestcpu

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Hi Faouz

There is a pretty straightforward way to get very close and then with just a bit more work make it exact.

You have to realize that when you delete one of the RGB channels is converts to what is called Spot Channels with CMY spot colors. You effectively have switched to CMYK without the K channel (more on this later)

Here are the simple steps
- Convert your image to a Smart Object
- Open that Smart Object
- Within the Smart Ojbect delete the blue channel and File Save (or Cmd/Cntl + S)
- Go back to your main file (that is in RGB) and Photoshop will display in RGB the desired image

The above are the simple steps that get you close. To get virtually exact, you need to have a CMYK profile that does not use K by creating a custom profile where you remove the black channel generation.

- Go to Edit > Color Settings
- In Working Spaces use the CMYK dropdown and choose Custom at the very top
- Type in a unique name (I used CMY)
- In the separation type use GCR and set the dropdown to None (this makes sure that Blacks are not created with the K channel)
- Leave the other settings at default and click OK
- Now to actually save this profile again go to the CMYK working spaces dropdown and chose the Save CMYK option. This will save this setting for future PS sessions.
- Now in both the main file (which has the single Layer Smart Object) and also in the opened Smart Ojbect file, use the Edit > Color Settings and set the CMYK workspace to your new unique CMY profile.

When I used the above it helps convert back from CMY to RGB more accurately.

So there is a way yet other posts show ways of getting very similar results without the above pushups.

Hope this is helpful.
 

Faouaz Alyagout

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Hi Thebestcpu,
The smart object method worked perfectly. At the end of the process I rastorized the smart object and saved and obtained the exact result I wanted. Thank you so so much :)
Fawaz
 

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