As for 8bit the as above but 8bit bitmap are very rare and almost dead format and most importantly it is very wide in range !, this format or to be more accurate the lack of unified/standardized format goes to 80s and the its color space is might hard to work with,
Actually, the 8 bit greyscale (Mono8) is a common format used in machine vision cameras. To use that in bitmaps, they need a
greyscale palette. Which then makes
access quite easy, because the byte value directly represents the brightness of the pixel.
Why working with 8bit Windows Bitmap (or 8bit DIB) is hard ? because When we talk Windows Bitmap then the there is a table define these 8bit colors representing 256 color value predefined to be used within this 8bit bitmap, so such bitmap will have lookup table with 256 value, the the pixel with grab the value form there, these values can be 8bit, 16bit.. 24bit color value..
As for generic 8 bit color bitmaps you are right: These are very uncommon nowadays, because memory and storage size are no longer limited and graphics cards / monitors generally use 24 bits or even more.