BMP (abbreviation of "bitmap") format is a standart format for storing device-independent and application-independent images in Windows. This format is rather simple and has no any tricky compression algorithms, so as usual BMP files are quite large but they are decoded/encoded quicker. Besides of it saving to BMP is lossless process (unlike for example JPEG).
A bitmap is an array of bits that specifies the color of each pixel in a rectangular array of pixels. The number of bits devoted to an individual pixel determines the number of colors that can be assigned to that pixel. For example, if each pixel is represented by 4 bits, then a given pixel can be assigned one of 16 different colors (2^4 = 16).
