Sizes of different image types?
Binary images are clearly smallest in terms of size, followed by indexed (paletted) images. RGB and greyscale images can take different sizes.

There are also (A)RGB images with sizes up to 48 bits but they usually include an extra alpha channel (for transparency purposes) so I haven't described them below.

RGB  (red, green, blue ) - 24 bits (each colour channel takes up 8 bits of space )

RGB (red, green, blue ) - 16 bits ( the green channel usually takes up 6 bits )

RGB (red, green, blue ) - 15 bits ( 5 bits per channel)

RGB (red, green, blue ) - 8 bits ( usually encoded as rrrgggbb )

Greyscale image - 8 - 24 bits ( each colour channel in a greyscale image has the same value)

Indexed image - usually 8 bits  ( the pixels don't carry colour information at all--rather they are indices into a colour table (i.e a palette). An 8-bit palette can hold 256 colours. While larger palettes are possible, they're rarely used because the most important reason to use a palette is to conserve space )

Binary image - 1 bit ( in a binary image, each pixel is stored as 1 bit. Since 1 bit can encode only 2 values (0 or 1), this kind of image can display only 2 colours (e.g black and white etc. )