BMP Color Depth Comparison

I took this picture at a pebbled cove of a black-sand beach in New Plymouth, New Zealand

1-bit color depth

4-bit color depth

8-bit color depth

24-bit color depth

rocks1Bit rocks4Bit rocks8Bit rocks24Bit
File Size 3 MB 12 MB 24 MB 72 MB

These .bmp file sizes are certainly what I expected. Lower color depths have less bits per color, and there are 8 bits per each byte.
The 24 bit image has 8-bits per channel (R,G,B), or 24-bits per pixel.
8-bit has 3 bits for red and green, and 2 bits for blue so 8 bits per pixel.
4-bit has 1 bit for each color, and 1 extra bit that is used for the specified color, so 4 bits per pixel.
1-bit uses only 1 bit per pixel, either black (0) or white (1).

Reference: http://r0k.us/graphics/colSpace.html