Bit Depth

Instructions: Read the following article and answer the questions at the end.  Write your answers in complete sentences. Use MS Word or another word processor to write your assignment. Submit your double-spaced work to the teacher after you spell-check, grammar check, and proofread.

Bit depth refers to how much color data a digital file can record for a single pixel. The more bits per pixel, the more colorful your images can be-up to a point. The most information that's ever used for displaying a file is 24 bits per pixel because the 16.8 million colors that can be displayed at that level are many more colors than any human eye can discern. However, there is an advantage to your camera or scanner being able to record and store more color information in a file. Thus, you have a much wider dynamic range. I've yet to see a prosumer or consumer digicam that captures more than 24 bits of information. On the other hand, many of the higher-end linear array cameras capture much more - sometimes as much as 48 bits of information. If you scan from film, 30-bits per pixel is the rule rather than the exception these days.

If you have a camera or scanner that's capable of capturing extended bit depth you should also find an image-processing program (Photoshop 5+ comes to mind) that will enable you to work in an extended bit-depth mode. Of course, you will eventually have to convert your image to a 24-bit file, but by then you'll at least be able to decide which range of 24 bits contains the information you want to keep.

Extended bit depth is also used for CMYK because each color channel of a true-color image needs to contain a full 256 levels of gray. This can't be accomplished at 24 bits per pixel because 4 x 8 is 32. Although no camera or recorder captures in CMYK, some high-end units immediately (or can be made to immediately) translate the image to CMYK. Just to make the discussion of bit depth a bit more confusing, extended bit depth can be used for other purposes, such as extra channels of data that can be used to store masks or texture maps. These are called alpha channels. Alpha channels are created by the program that uses them. Each alpha channel is 8 bits deep. So the more alpha channels you add, the deeper the bit depth of the image becomes.

Finally, all images that are less than true color contain fewer than 24 bits per pixel. If you have fewer colors in your image, you will have fewer bits per pixel. Table 6-1 lists the bit depth and corresponding number of colors.

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