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