Adjusting Levels while in channels

I understand the basics of using levels to adjust the dark and light values in an image.

1. )How do you go into each individual R, G, and B channels and adjust them with levels? What should I be looking for?

When using levels on the composite image, I look at the overall image when adjusting levels, what do you look for when looking at the image when viewing it through the R channel with the red cast over it?

2.) what is the advantage of doing it this way?

Thanks!

You don't have to look just at any particuluar channel to make an adjustment on it. While you're in the composite channel, and in the Levels dialog box, simply click on the Channel drop down option and select the channel you want, making your adjustments while viewing the composite.

Ok, I just did it the way you suggested and I didn't get the cast that I get the other way.

So should I adjust the levels this way always, for each individual channel from the drop down whenever I need to adjust levels?

Yes.

The "cast" that you got is really from the option you have chosen in the preferences to show channels in color. They are really black and white channels representing the relative intensity of red, green and blue colors, and you can set the preferences to show them to you that way. As you progress in your Photoshop skills, you will find good use for "seeing" the channels in black and white - and later on you can think about using Curves instead of Levels...

Thanks for your help. Just for final clarification so I understand from a technical point of veiw:

1. What does doing levels on each channel individually accomplish over doing it on the image as a whole? Is it just more accurate?

Thanks.

No, it's different, when you adjust the levels of individual channels, you're manipulating the brightness (the "amount") of that specific color in the highlights, midtones, or shadows of your image.

When you adjust levels in the composite, you're changing OVERALL brightness and contrast (and can introduce color shifts in the process).

So you shouldn't always do it one way or the other. If you're wanting to, for example, reduce a color cast (or introduce one), you can adjust by channel. If you want instead to increase or decrease the overall brightness or contrast of an image you'd more likely use the composite "channel."

But understand that, once you get to this level of image manipulation, you might find Curves, Hue/Saturation, Selective Color, and even the new Match Color to be more sensitive, "surgical" adjustment tools.