Possible to delete color channels? (Photo/Publisher)

[UdoBerlin]

I would like to keep only the cyan channel in a CMYK image and export to PDF.

[Dan C]

Hi UdoBerlin, 

You can use the curves adjustment to reduce the YMK to 0. (dragging the right node to the bottom on each channel aside from alpha)

Lee

[Dan C]

Hi @UdoBerlin,

Another option is the following:

• If your document has multiple layers, right click the top layer and select 'Merge Visible', to create one new Pixel layer with a full representation of the document.
• Select this Layer in the Layers Studio and navigate to the Channels Studio
• Right click on Pixel Magenta & Pixel Yellow, selecting Clear in the menu that appears.
  Note you will now need to decide if you wish to include the Black channel or not
• If you wish to include this, you can export the image as-is, if not, please right click and select Fill for the Black channel

Please see my screen recording below showing this -

 
I hope this helps  

[UdoBerlin]

Thanks to both of you!  Dan’s answer was exactly what I wanted.

[walt.farrell]

2 hours ago, Dan C said:

• Note you will now need to decide if you wish to include the Black channel or not
• If you wish to include this, you can export the image as-is, if not, please right click and select Fill for the Black channel

I'm curious about that, Dan. I had never tried clearing channels before, so I tried your instructions.

I was surprised to note that if I Clear (rather than Filling) the Black channel at the final step, I lose the entire image. Why does that happen?

[R C-R]

7 hours ago, Dan C said:

Another option is the following:

Just wanted to mention that a macro could be made to do this in one step. It could be one of several in a custom macro library category, of six related macros, one each for C, Y, M reductions with & without retaining the black layer.

That said, I am also surprised that clearing the black channel rather than filling it turns the layer black. 

[thomaso]

17 hours ago, walt.farrell said:

I was surprised to note that if I Clear (rather than Filling) the Black channel at the final step, I lose the entire image. Why does that happen?

You don't lose the entire image, it's just that black gets most dominant as it represents luminosity/brightness in CMY + K (…displayed with an RGB hardware). If you then invert Black, the image "comes back" but pale (= empty composite black channel).

I am rather confused that Filling and Clearing CMY appear both the same AND work opposite to Black. Or: CMY get filled with White while K gets filled with Black. If I use "Clear" (or "Fill") for CYAN it needs to get inverted before I see the expected CYAN domination whereas Clearing Black shows directly the black. Is here the difference of additive / subtractive working that needs to get "repaired"?

[Dan C]

18 hours ago, walt.farrell said:

I was surprised to note that if I Clear (rather than Filling) the Black channel at the final step, I lose the entire image. Why does that happen?

13 hours ago, R C-R said:

That said, I am also surprised that clearing the black channel rather than filling it turns the layer black. 

11 hours ago, thomaso said:

I am rather confused that Filling and Clearing CMY appear both the same AND work opposite to Black. Or: CMY get filled with White while K gets filled with Black. If I use "Clear" (or "Fill") for CYAN it needs to get inverted before I see the expected CYAN domination whereas Clearing Black shows directly the black. Is here the difference of additive / subtractive working that needs to get "repaired"?

I've been discussing this internally and we believe it may be an oversight from RGB/A documents, where the 4th channel is calculated as the 'Alpha' - therefore using 'Clear' on the Alpha would fill the channel in black (removing all Alpha) and using 'Fill' on the Alpha would set the channel to be empty (filled with 'Alpha').

When in a CMYK document, the K channel seems to be incorrectly using the same understanding as above - but I believe it should be the same behaviour as the CMY channels, so I'm logging this as a bug with our devs now

[thomaso]

28 minutes ago, Dan C said:

but I believe it should be the same behaviour as the CMY channels

Yes, but shouldn't for all 4 channels "Clear" cause an empty channel (white) and "Fill" cause full color (c, y, m, k)?
Currently it's different for CMY: both, Clear + Fill, result in a cleared, empty channel while it requires additionally "invert" to get it filled.

[Dan C]

17 minutes ago, thomaso said:

Currently it's different for CMY: both, Clear + Fill, result in a cleared, empty channel while it requires additionally "invert" to get it filled.

Sorry, I had misunderstood that part of your post and was focusing on the K channel - I can see the issue here, I would expect 'Fill' on a C channel to fill with Cyan, as this happens when using 'Fill' on the R channel in an RGB document, so I'm logging this with our devs also