BMP files are still-image bitmap files in the Windows bitmap (.bmp) format.
When BMP is chosen as the output format, clicking Render or Setup on the Render Output File dialog displays the BMP Compression dialog.
8 Bit Optimized palette (256 Colors)—Choose to render a smaller, 8-bit color file.
RGB 24 bit (16.7 Million Colors)—Choose to render a larger, true color (24-bit) file.