Understanding Bit Depth

FIGURE 12.3

The scan resolution will show up in Photoshop as the Image Size.

5.Exit the scanning software and save the image with a new name. You can now edit it and print it, depending on the resolution.

A bit is the foundation for all computing: it’s the smallest unit of data—a one or a zero. Bit depth is directly related to the amount of data (bits) a scanner or camera captures per pixel. Most scannersoftware provides several scanning bit depths, such as 24-, 36-, and 48-bit depth. Eight bits make up a byte. A byteis a handy way to group bits (1 or 0). Two to the eighth power equals 256. Therefore, 8 bits of data (a byte) can have 256 different values (0–255) (see Table 12.3). For simplicity, let’s call each value a brightness.

Table 12.3 Bit Depth and CorrespondingRGB Colors

Number of Bit Depth Values Available Values Available in an RGB Image

1 2 Not applicable 2 4 2×2×2 = 8 color values. Only applicable to a GIF image (indexed color in Photoshop) 4 16 4×4×4 = 16 color values. Only applicable to a GIF image (indexed color in Photoshop) 8 256 8(R)×8(G)×8(B) = 24 bits = 16,777,216 values 12 4096 12(R)×12(G)×12(B) = 36 bits = 68,719,476,736 values 16 16,384 16(R)×16(G)×16(B) = 48 bits = 281,474,976,710,656 values