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Color modes

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» 4. 8-bit Indexed & Grayscale

8-bit Indexed color

Some image formats (like GIF) can only handle 8-bit color depths. These image formats assign 3 bits for two of the primary RGB colors and 2 more bits for the remaining color. By using this 3-3-2 bit combination they can form up to 256 colors. This color "selection" is called color indexing.

8-bit indexed color images are usually lighter than their 24 or 32-bit counterparts and, due to their color limitations, are better suited for logos and other simple graphics.

Indexed-color image
Figure 4  8-bit indexed color image
Indexed color palette
Figure 5  256-color palette used
for Figure 4

8-bit Grayscale

A grayscale image uses only 8 bits to represent 256 shades of gray, resulting in Black-&-White- like images.

Grayscale-color image
Figure 6  8-bit indexed color image
Grayscale color palette
Figure 7  256-shades of gray
palette used for Figure 6

Note: There are also a few image file formats that support a 16-bit grayscale mode natively (allowing up to 65,536 shades of gray), although browsers and many imaging programs tend to ignore this extra information and adapt it to 8 bits.

More pages of this tutorial → Color modes  <1234

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