: Photoshop: Channel use cases? I understand channel just store color information for an image. But in the real world, what are the actual use cases?

@Harper654

When taking pictures with an infrared filter in front of the sensor, the results often appear pink and unpleasing.

Here's an example of what a picture could look like straight-out-of-camera:


After white balance adjustments, clouds are white again but the sky still looks weird:


By switching the red and blue channels, the sky becomes blue again:

St Lawrence, Stratford-sub-Castle, in infrared..

Note that the first picture isn't the original one. I didn't have access to the RAW file, so I applied the described process in reverse to show the steps.

Here's a youtube video describing this process : "Color Infrared Channel Swap in Photoshop". The swap is done with Channel Mixer but could also be done by copy-pasting the Red and Blue channels.

David Keochkerian is a photographer who took many great IR pictures (example).

His workflow is described here and here. Red/Blue channel swap is mentioned in both.

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@Caterina889

Channels don't only store color.

They can store transparency (alpha) as well. In fact every single layer mask in Photoshop creates an alpha channel.

While alpha channels may not be what one immediately thinks about when thinking of "channels", rest assured there would be no such thing as transparency in Photoshop without channels.

I start almost all extractions with a selection based upon a color channel. Convert it to an alpha channel and refine.

Example: How to remove white background in Photoshop

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@Sarah814

It's extremely useful for the press industry.

Color separation is important.

It's the only way you can clean up crappy non-vector art for the printing press.

For example, prepress has to use Photoshop channels to bring specific colors up to a certain % in order to get enough dot gain for the image to look clean.




To reproduce color and continuous-tone images, printers usually
separate artwork into four plates (called process colors)—one plate
for each of the cyan, magenta, yellow, and black portions of the
image. You can also include custom inks (called spot colors). In this
case, a separate plate is created for each spot color. When inked with
the appropriate color and printed in register with one another, these
colors combine to reproduce the original artwork. helpx.adobe.com/illustrator/using/printing-color-separations.html

That quote is for Illustrator but the same concept applies to Photoshop when dealing with the press industry. You won't always have vector art that has easy color manipulation

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@Vandalay110

Keying. Channels can be used as a starting point for very fast and very accurate selections.
Storing selections. Storing a selection allows you to do filters and math operations on it.
Storing color channels for spot colors. In other words you want to have that golden color on your print or you want varnish on specified locations or just orange.
Un-premultiplying color.
Viewing raw channel info.

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