Bit Depth and Photoshop Elements 10
An important item to understand about color channels is bit depth. A bit holds one of two values; one value is for black, the other for white. The common bit depth of images displayed on your computer monitor is 24.
When you have 256 levels of gray, you’re working with an 8-bit-per-channel image — 8 bits with two possible values each is 28, or 256, possible levels of gray. Multiply 8 bits per channel by 3 channels (the red, green, and blue channels), and you get 24 bits.
Take a look at the Image→Mode menu. You should see a menu selection that says 8 Bits/Channel. When you open an image in Elements, if this menu command is grayed out, you’re working with a 24-bit image, or an image of 8 bits per channel.
What does it mean when you can select the 8 Bits/Channel menu command? You can be certain that your image isn’t an 8-bit-per-channel image. You may be able to select this command because some digital cameras and most low-end, consumer-grade scanners can capture images at higher bit depths.
You can scan a photo on a scanner at 16 bits per channel. When you do, you end up with many more levels of gray. When you take a picture with a quality digital camera, you can capture 16-bit-per-channel images, and you end up with a file containing more than 4,000 levels of gray.
Now, here’s the catch. All files need to be reduced to 8 bits per channel before you print them because that’s all the information any printer uses. In addition, many tools, commands, and panel options work only with 8-bit-per-channel images. So, you ask, What’s the benefit of acquiring images at higher bit depths than I can print them?
If you attempt to adjust brightness and contrast, or make other image enhancements, in an 8-bit-per-channel image, you often destroy some data. You can cause some noticeable image degradation if you move adjustment sliders too far while working with 8-bit-per-channel images.
When you edit your 16-bit and 32-bit images, you don’t destroy data — you simply inform Elements which 256 of the total available levels of gray you want to use. The result is an image with more continuous gray tones than you can achieve in 8-bit-per-channel images.