Color Bit Depth and Why It Matters

Bit depth is a way to describe how much color information is available about each pixel in an image. It's also called color depth or pixel depth and, as with so many other things, more is better. Greater bit depth (more bits of information per pixel) means more available colors and more accurate color representation in your digital pictures. Consider this: a pixel with a bit depth of 1 has only 2 possible values, either black or white. A grayscale pixel with a bit depth of 8 has 2 to the 8th power, or 256 possible values. And a pixel with a bit depth of 24 has 2 to the 24th power, or about 16 million, possible values. Common values for bit depth range from 1 to 64 bits per pixel. You will find that your Photoshop images tend to be either 8-bit or 16-bit. More information means larger files and longer times, of course. And it also means truer color.

8-Bit Color

It's actually a little bit misleading to call 8-bit color by that name . Depending on the color mode you've chosen to work in, you have anywhere from 8 to 32 bits of information for each pixel. In RBG mode, you have 8 bits each of the red, blue, and green color channels, making 24 bits of color information. In CMYK mode, you have 8 bits each of four channels, or 32 bits in all.

16-Bit Color

In previous versions of Photoshop, not all of the tools and filters worked with 16-bit color. As of Photoshop CS2, all tools and most filters are 16-bit compatible. Does this mean you should do all your work in 16-bit color? No. Technology moves forward in uneven leaps. Even though Photoshop can work in 16-bit color, your monitor can't show you all the millions of colors your image has. And your home/office inkjet or color laser printer can't possibly reproduce them. Within a year or so, this might change as new HDTV monitors and better printing inks come on the market. Adobe has, in effect, raised the bar, and now makers of monitors and printers will have to jump that much higher. The next frontier? 32-bit colorbut Photoshop's support for it at this point is still so limited that it's best to leave it alone.