question about channels?

DD
Posted By
Digga Downs
Sep 13, 2003
Views
544
Replies
6
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Closed
What is the difference between a channel and a layer?

what are the 3 types of channels and how are they used?

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Y
YrbkMgr
Sep 13, 2003
Sounds like questions from the test.

Dude, read the online helpfile (F1), do a search for your terms. It’s an electronic reproduction of the manual and a great resource.
DD
Digga Downs
Sep 13, 2003
Thanks!
Y
YrbkMgr
Sep 13, 2003
I should add, that if you do the search, and have difficulty understanding what you are reading, come back and ask specific questions, like "okay, I know this and that, but does that mean this? Or this?" If you get my point…
DD
Digga Downs
Sep 14, 2003
used help and still cant find the 3 different types of channels or how they are used?
Y
YrbkMgr
Sep 14, 2003
Copy and pasted directly from the Help File:

Channels are grayscale images that store different types of information:

* Color information channels are created automatically when you open a new image. The image’s color mode determines the number of color channels created. For example, an RGB image has four default channels: one for each of the red, green, and blue colors plus a composite channel used for editing the image.

* You can create alpha channels to store selections as 8-bit grayscale images. You use alpha channels to create and store masks, which let you manipulate, isolate, and protect specific parts of an image. In addition to supporting alpha channels from Photoshop, you can save, load, and delete selections as alpha channels in ImageReady 7.0.

* You can create spot color channels to specify additional plates for printing with spot color inks.
GD
glen deman
Sep 14, 2003
Here are some ways I use channels.

When you click on the channels tab, you see the Red, Green, Blue, and composite (RGB) channel. Let’s say you use the magic wand to select various parts of an image; now you have a complicated selection, and if you ever want to go back and make the same selection, you’d have to do the whole thing over. Instead, you can store a selection in the alpha channel. Go to select>save selection. When you save it, a new channel will be created (this is the alpha channel). You will see that it is a black and white image; the white areas are the ones that will be affected and the black areas are "masked" off. Not only can you save complicated selections, but you can also easily modify the mask by painting in areas. If you want to add something to the selection, paint in white and visa versa to subtract. In this way you can really fine tune a selection. Oh, you can also blur the mask to feather the selection.

In an image, you sometimes have a lot of noise. If you try to simply do a median>noise operation, you will blur the whole picture. However, in many cases that noise is mostly present in the blue channel. So, if you de-noise the blue channel by itself, you get rid of some noise without losing definition in the picture.

Sometimes you want to isolate an object from it’s background. In RGB mode, there may not be a lot of contrast between the two. However, in certain channels, that contrast might be increased. So, if in the green channel there’s a large contrast, you can copy that channel, paste it into a new channel, and use levels to create even more contrast. Now you can fine tune this mask and it will be a tight selection of your desired object.

There are other advanced things you can do with channels, of course.

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