Inspiring

Answered

Problem inverting a single channel

Forum|Forum|7 years ago
November 2, 2018
6 replies
3772 views

This topic has been closed for replies.

Correct answer jane-e

Hi Doc_Pit

There are two kinds of channels: color and alpha.

The color channels store colors. A couple of examples:

Greyscale: one color channel for shades of grey
RGB: three color channels for Red, Green, Blue
CMYK: four color channels for Cyan, Magenta, Red, Black

There are other color modes.

Alpha channels are also saved selections.

Make a selection > Go to Selection > Save Selection > Name it > It will show up as an alpha channel.

What the tutorial is showing you is called channel masking, meaning make a selection out of a color channel. (Stay with me; I’ll keep it simple!) The idea is that you pick the color channel with the best contrast and copy it. It then stops being a color channel, and becomes an alpha channel. You can leave it named “Red Copy”, but most people would rename it. In the tutorial, I imagine you then go on to clean up the alpha channel to make it more pure black and pure white.

As soon as it is an alpha channel, whether you got it by making and saving a selection or by copying a color channel and cleaning it up, you can go to Select > Load Selection and find it listed there. Copying it converts it to an alpha channel.

Back in the days of CS3, I watched Deke McClelland’s 33 hour tutorial on Channels and Masks several times. This, as I said, is a very brief explanation, but there is more when you are ready for it. It’s fun stuff!

Does this make sense?

Chuck Uebele

Community Expert

Glad you like the forums. There are a lot of knowledgeable people here who donate their time to help.

Doc_PitAuthor

Inspiring

Just want to take a minute to say, it never ceases to amaze me how generous people in this forum are in giving their time to help others. Over the last several years, I've made much more progress than I could ever have made without that help. Many thanks.

jane-e

Community Expert

Thank you for your kind words, Doc_Pit!

Chuck Uebele

Community Expert

By any chance did, did you try inverting it using the main menu? Once in a while my shortcut keys don't work. No idea why.

Doc_PitAuthor

Inspiring

Chuck, I just tried Image>Calculations and checked the Invert box. Yes, that works. Thanks.

jane-e

Community Expert

So glad it’s working!

Semaphoric

Community Expert

Clicking on one channel should select it, and Control+I will invert it:

jane-e

Community Expert

Yes, but in his screen shot of the tutorial, it is on the alpha channel. I suspect he has the composite RGB selected which is why it’s not working.

jane-e

Community Expert

Notice that in your screen shot, he copied the red channel to make an alpha channel. The alpha channel “red copy” is the only channel that is selected or visible.

Since this does not work for you, check to see which channels are selected and visible. It should be only the alpha channel. You can use the keyboard shortcuts to make the alpha channel active and visible, but they won’t be the same shortcuts as in the tutorial. They changed shortly after that, so look at your own panel.

And a favor: do not put your text as a screenshot, as we have an international audience, and they cannot translate a picture. If you post the text, a moderator can include it in your original post. Thank you!!

Does it work now? If not, show your own Channels panel.

Doc_PitAuthor

Inspiring

Thanks to everyone for the responses.

1) Regarding the text/screenshot advice. It never occurred to me. I'll certainly correct that.

2) Jane, when you say "he copied the red channel to make an alpha channel," you lose me. My impression is that we have the composite (RGB) channel and the 3 alpha channels; i.e., the red channel IS an alpha channel. Copying the red channel simply duplicates an existing alpha channel. Not so?

3) Each time I attempted to invert, I selected and made visible only one channel: either R or G or B. Not composite. However, as you indicated, I copied a channel (in this case, the B channel), did a Ctrl+I, and it did invert the channel. If I try it on the B channel, it will not invert, but on the blue copy it will. Because I was just experimenting, I was working on the channel itself. Normally, I would be working on a duplicate channel anyway.

Don't understand why Ctrl+I will not invert the channel but will invert a copy. Since it's good practice to work on a copy, perhaps they are just enforcing best practices. I very much appreciate the help.

jane-e

Correct answer

Community Expert

Hi Doc_Pit

There are two kinds of channels: color and alpha.

The color channels store colors. A couple of examples:

Greyscale: one color channel for shades of grey
RGB: three color channels for Red, Green, Blue
CMYK: four color channels for Cyan, Magenta, Red, Black

There are other color modes.

Alpha channels are also saved selections.

Make a selection > Go to Selection > Save Selection > Name it > It will show up as an alpha channel.

What the tutorial is showing you is called channel masking, meaning make a selection out of a color channel. (Stay with me; I’ll keep it simple!) The idea is that you pick the color channel with the best contrast and copy it. It then stops being a color channel, and becomes an alpha channel. You can leave it named “Red Copy”, but most people would rename it. In the tutorial, I imagine you then go on to clean up the alpha channel to make it more pure black and pure white.

As soon as it is an alpha channel, whether you got it by making and saving a selection or by copying a color channel and cleaning it up, you can go to Select > Load Selection and find it listed there. Copying it converts it to an alpha channel.

Back in the days of CS3, I watched Deke McClelland’s 33 hour tutorial on Channels and Masks several times. This, as I said, is a very brief explanation, but there is more when you are ready for it. It’s fun stuff!

Does this make sense?

Chuck Uebele

Community Expert

It should work.

Sign up

To post, reply, or follow discussions, please sign in with your Adobe ID.

Sign in to Adobe Community

To post, reply, or follow discussions, please sign in with your Adobe ID.

Scanning file for viruses.

This file cannot be downloaded