Choose the Correct Photoshop Mode: LAB, Multichannel, Bit Depth
Choose Image→Mode to view image mode choices available in Adobe Photoshop CS5. Selecting the right one for an image is important because each mode offers different capabilities and results.
The LAB (Lightness, A channel, and B channel) color mode is used by many high-end color professionals use because of its wide color range. Using LAB, you can make adjustments to luminosity (lightness) without affecting color. In this mode, you can select and change an L (lightness or luminosity) channel without affecting the A channel (green and red) and the B channel (blue and yellow).
LAB mode is also good to use if you’re in a color-managed environment and want to easily move from one color system to another with no loss of color.
Some professionals prefer to sharpen images in LAB mode because they can select just the Lightness channel and choose Filter→Sharpen→Unsharp Mask to sharpen only the gray matter of the image, leaving the color noise-free.
Multichannel is used for many things; you can end up in this mode and not know how you got there. Deleting a channel from an RGB, a CMYK, or a LAB image automatically converts the image to Multichannel mode. This mode supports multiple spot colors.
You have more functionality in 16-bit and even 32-bit mode. Depending on your needs, you may spend most of your time in 8-bit mode, which is more than likely all you need.
Bit depth, or pixel depth or color depth, measures how much color information is available to display or print each pixel in an image. Greater bit depth means more available colors and more accurate color representation in the digital image. In Photoshop, this increase in accuracy also limits some available features, so don’t use it unless you have a specific request or need for it.
To use 16-bit or 32-bit color mode, you also must have a source to provide you with that information, such as a scanner or camera that offers a choice to scan in either mode.