PhotoShop Channels

JD
Posted By
James Douglas
Feb 16, 2006
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339
Replies
2
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Closed
I am studying Photoshop and the most recent lesson is using channels. Within the lesson we lasso’d portions of a photo and saved and loaded when needed with the saved selection in place.

My question is what do other’s use "channels" for? Saving selected portions of work to bring back w/o having to go through the selection process again.

BTW, I am doing the lesson again, and again until I throughly understand where I can apply channels to the work I am doing.

Thanks!
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Mike Russell
Feb 16, 2006
"James Douglas" wrote in message
I am studying Photoshop and the most recent lesson is using channels. Within the lesson we lasso’d portions of a photo and saved and loaded when needed with the saved selection in place.

My question is what do other’s use "channels" for? Saving selected portions of work to bring back w/o having to go through the selection process again.

For a picture, a channel is a two dimensional "plane" of pixel data associated with the picture. A black and white image has a minimum of one channel, a brightness value for each pixel. A color image has three or four channels of color data, normally (but not always) a red, green, and blue value for each pixel. You can also create a channel by saving a selection – this kind of channel is called a mask or an alpha channel.

BTW, I am doing the lesson again, and again until I throughly understand where I can apply channels to the work I am doing.

This is a good approach. I’d suggest coming at channels also from the direction of practical knowledge. If you can make a lasso selection, use quick mask mode, or use curves on red, green, and blue, you have some working knowledge of what a channel is. As various light bulbs will turn on and you will tie what you’ve read and what you can do together.

One of my favorite articles about this is Alvy Ray Smith’s one about the alpha channel, and how it relates to masking techniques that were used in the motion picture industry.
ftp://ftp.alvyray.com/Acrobat/7_Alpha.pdf
http://www.alvyray.com/Memos/MemosMicrosoft.htm
—
Mike Russell
www.curvemeister.com
U
usenet
Feb 16, 2006
James Douglas wrote:

I am studying Photoshop and the most recent lesson is using channels. Within the lesson we lasso’d portions of a photo and saved and loaded when needed with the saved selection in place.

My question is what do other’s use "channels" for? Saving selected portions of work to bring back w/o having to go through the selection process again.

BTW, I am doing the lesson again, and again until I throughly understand where I can apply channels to the work I am doing.

A channel is a mask. The R channel, for instance, masks (or reveals) red values. You can modify the visible channels of your picture… For instance, open up a picture, select its R channel, and then modify it with Curves, or even just brightness/contrast. Go back to the RGB channel and see what you hath wrought. The degree to which red is masked will have changed, because you changed the R channel.

Given that channels, even visible ones, are just masks, it stands to reason that you’d be able to save a selection (a mask) in a channel.

And you can also modify the selection using all your normal tools, just like with the visible channel. Make a new channel, paint on it, and then load it as a selection. The quickmask feature is a shortcut to this process.

As far as what *I* use channels for: Color correction in LAB mode always makes me happy. 🙂

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