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Saving only one color channel

Forum|Forum|3 years ago
May 9, 2022
8 replies
17822 views

Hello. I have an Infrared image from which I would like to extract only the red channel and save it as another image. How can I do this? TIA

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Correct answer Semaphoric

Yet another way would be to use Image > Calculations, with Result set to New Document.

D

Dominik Csordás

Participant

Hello,

Kind of late answer, but I also use the "Image - Calculations". Save the results to new document, and use normal blending.

Then you can convert the image from "Multichannel" to "Grayscale", and you can save as JPG, or whatever format you would like.

TheDigitalDog

Inspiring

All four techniques produce indentical results; use whatever method you desire:

Yet another option, with the red channel active/targeted/selected, using Image > Mode > Grayscale will use the R channel and discard the G and B channels
Yet another way would be to use Image > Calculations, with Result set to New Document.
One way would be to duplicate the file, convert to grayscale, then use apply image and use the original image's red channel as the source to apply to the new file's gray channel. (note: Bend must be set to normal)
Use the Split Channels command. You'll end up with three channels, save the Red channel.

Channel mixer, default doesn't:

Author “Color Management for Photographers" & "Photoshop CC Color Management/pluralsight"

D Fosse

Community Expert

Everything should always display correctly in Photoshop, with full grayscale color management.

My concern is that most files will eventually be used for something (outside Photoshop). That's when this problem shows up, when color management stops. No other application does color management for grayscale, not even the color managed ones. So it's just like any other non-color managed situation.

I feel I'm not getting much traction here, so I'll take a hint and drop it 😉 I just thought it might be useful to be aware of it and take precautions.

TheDigitalDog

Inspiring

My concern is that most files will eventually be used for something (outside Photoshop). That's when this problem shows up, when color management stops

That's true for any image document, as you know; grayscale, RGB, anything. That isn't the topic or question here. Which is why you're not getting traction.

There are four processes that actually accomplish what the OP asked for, some with more steps than others but all that produce identical results. The Channel Mixer doesn't. It isn't (unless you specify an exact setting) providing just the red channel like the others.

Author “Color Management for Photographers" & "Photoshop CC Color Management/pluralsight"

Semaphoric

Correct answer

Community Expert

Yet another way would be to use Image > Calculations, with Result set to New Document.

Stephen Marsh

Community Expert

Yet another option, with the red channel active/targeted/selected, using Image > Mode > Grayscale will use the R channel and discard the G and B channels:

G

gma_ArtsAuthor

Participating Frequently

OK thanks all. Using the info provided I have been able to do it. Thanks again.

Kukurykus

Legend

You did? Mark the correct replies as result...

D Fosse

Community Expert

Well, I certainly didn't. Just read through to the end 😉

TheDigitalDog

Inspiring

Use the Split Channels command. You'll end up with three channels, save the Red channel.

Author “Color Management for Photographers" & "Photoshop CC Color Management/pluralsight"

D Fosse

Community Expert

But what grayscale profile? You get three untagged grayscale files.

In Photoshop you will see them as Dot Gain 15 or 20% because that's the default working gray in Photoshop (if you haven't changed anything). But they won't be seen like that outside Photoshop! Most likely they will be seen as gamma 2.2, at least for screen, which is very different from dot gain 15/20.

Which is why monochrome RGB is much safer.

TheDigitalDog

Inspiring

Tag the channel/doc.

By @TheDigitalDog

My point was that this will change the appearance, and that may not be what the OP wants. It will look wrong outside Photoshop:

To make it look right outside Photoshop, assign the working gray and then convert to gamma 2.2, which at least has the greatest likelihood of looking right on screen.

Or avoid this whole can of worms by keeping the image RGB and use Channel Mixer.

It should only “look wrong” if tagged incorrectly. The data is the data, the OP at this point wants one specific color channel that exists. He doesn't want a mix of channels AFAIK.

Author “Color Management for Photographers" & "Photoshop CC Color Management/pluralsight"

D Fosse

Community Expert

The safest way is the Channel Mixer, which retains the file as monochrome RGB in the original color space. It will duplicate one channel into the other two. Or simply copy the red channel and paste into the other two.

You can always copy a single channel and paste it into a new grayscale file, but then you need to be very careful which grayscale profile you choose, or you will get significant tone curve changes. The reason is that icc grayscale profiles aren't supported anywhere outside Photoshop, and so you need to use a profile that matches the output conditions whatever they happen to be. For this reason, I generally advise against grayscale unless you're very confident and know what you're doing.

Chuck Uebele

Community Expert

Lots of ways. One way would be to duplicate the file, convert to grayscale, then use apply image and use the original image's red channel as the source to apply to the new file's gray channel.

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