Channels in Photoshop
I was messing around with color options in photoshop, just exploring what I could do, when I decided to look at something I normally browse over: the channels panel, at the bottom next to layers. I found something pretty cool, too. If you de-select two of the color options, leaving just one with that open eye next to it, you turn the image black and white and gray only. Even cooler, each color by itself creates a different black and white image, with different parts brighter and darker than the others.
After digging around, I discovered that this is actually how photoshop interprets a picture. It sees three different black and white pictures, one for each main color of light (red, green and blue). The lighter a part of an image, the more light was recorded there, which means more of that color goes there (on that range from 0 to 255). This means that, if a spot on your picture is heavily red, it actually just sees a bright area of gray on its green channel. That’s how photoshop interprets pictures: in shades of gray.
You can see this in any spot on your picture by choosing Window->Info, which will make a little dialog box pop up. When you move your cursor over a spot in your picture, that info pane will show various things, like the x, y position of your cursor, but in the top left of the window it’ll show how much of each color photoshop put into the pixels at that location.
So if you ever get the urge to see how photoshop sees things, just get selective with the channels pane. Maybe you’ll like the new view, too.
Edit (Feb 8 2010; original Jan 20 2010): You can imitate these views using the Channel Mixer in the adjustments pane. The top drop-down that appears in that pane lets you enact these imitations almost automatically; if you like the black-and-white image you get when only the blue channel is selected, just drop down to “Black & White with Blue Filter (RGB).” You can also manually adjust the amount of color output of each channel by using the next drop-down (Output Channel), selecting the appropriate channel, then using the color sliders to modify it. It’s a lot harder to get a black-and-white image using just the sliders, but you can get some surreal colors going on.
~Jon B Kimmel