Originally Posted by slipe
An 8 bit pixel is simply a series of three 8 digit binary codes. 8 binary digits can have 156 possible values in 10base, so there are 156 possible values for red, green and blue. 156 X 156 X 156 gives 3,796,416 possible colors from an 8 bit pixel. The full image file has other information about the relative position of the pixels, compression or decoding information, layers, the size the file would print at etc. But the pixels are simply code that represents a color.
156 should be corrected to 256 (and 256 x 256 x 256 = 16,777,216). Also I would not call this an 8bit pixel, it is 24bit.
The only reason to refer to an n-bit pixel is so you know the range of different values a pixel can have without knowing anything else about the sensor. Therefore it does not make much sense to refer to an 8bit pixel in case of 3 x 8 bits (8 bits per channel).