How to create color image from three filtered monochrome images

[LarsHP]

I am trying to find out how to create a color image like astrophotographers do when filtering various wavelengths with a monochrome camera and then blending them together into an RGB image. I understand that it must be some kind of layer work, but how?

Each of the (typically) three monochrome image can be colorized like this: 

Image -> Adjustments -> Channel Mixer -> zero two of the colors for each image.

After the three monochrome images are saved as respectively red, green and blue only images, the idea is to mix these three in layers into a single full color image.

Here is an example where the photographer used some other software, but since I already pay for Adobe CC Photography, I want to use that.

So, what would be a way to mix these three color images into an RGB image?

[Stephen Marsh]

Although it could be done with layers, using channels would be easier if each image was suitable.

[LarsHP]

Thanks for the suggestion, but I don't understand how using channels alone would create the wanted result? I would of course need to stack the three colorized images first, but when deselecting the respective colors for each layer in the Channels panel, I just get a black image.

[Stephen Marsh]

No need for layers and stacking.

RGB colour images are directly created from RGB channels.

Layers just add an extra unnecessary, indirect abstraction. Most image formats don't support layers, but channels are an intrinsic part of their construction.

Open the three separate files. Copy the green channel data from the green file and paste it into the green channel of the red file. Copy the blue channel data from the blue file and paste it into the blue channel of the red file. Then reselect the primary composite/component RGB channel to view the combined result.

This can be automated into an action if you have to do this on a regular basis.

[LarsHP]

I understand what you say, but how to copy one channel to the channel of another image is beyond my Photoshop abilities. The suggestion D Fosse issued is straightforward and easy for me to understand and do, so I think I will stick to that. Thanks for your contribution, though.

[Stephen Marsh]

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@LarsHP wrote:

I understand what you say, but how to copy one channel to the channel of another image is beyond my Photoshop abilities. The suggestion D Fosse issued is straightforward and easy for me to understand and do, so I think I will stick to that. Thanks for your contribution, though.

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You simply go to the channels panel in the green document, click on the green channel, select all, copy, then go to the red document, select the green channel, select all and paste. Then repeat for the blue.

Another method is to use Image > Apply Image to "stamp" channel data from one document channel to another document channel.

It's more direct and simpler than messing with layers. I encourage you to expand your repertoire.

[LarsHP]

Thanks for your effort. After testing your method, I can see I get the wanted result, thanks. This method of course requires the source images to be perfectly aligned. If they aren't, it will require something like using the stacking script and the method D Fosse suggests.

[Stephen Marsh]

I'm glad that you stuck with it!

As you didn't provide any samples all I had to go by was the example link and the separated images that were in proper alignment/register. It's possible to align channel content, however I understand that you are more comfortable with layers.

[D Fosse · Accepted solution]

As layers you'd stack them and put them in Screen blend mode.

[LarsHP]

Thanks! This suggestion was easy to understand and helpful.