Fanning Software Consulting

What do BSQ, BIL, and BIP mean, really?

QUESTION: Alright. I get terribly confused with all the nomenclature. What do BSQ, BIL, and BIP mean, really, when used in conjunction with images?

ANSWER: BSQ, BIL, and BIP represent ways of storing 24-bit images in memory or on disk. The initials stand for band-sequential, band-interleaved-by-line, and band-interleaved-by-pixel, respectively. These image formats are also sometimes called "band-interleaved", "row-interleaved", and "pixel-interleaved", respectively.

Twenty-four bit images always have 3 "bands", which represent the red, green, and blue image planes. But the "3" in the image dimension can come in different positions. The table below shows you the dimensions of the image, and the different nomenclature. Note that the dimension M is the column dimension. This is sometimes called the number of samples in the image. The dimension N is the row dimension, and is sometimes called the number of lines in the image. The dimension 3 is equivalent to the number of bands in the image, and is always three in a 24-bit image. In multi-spectral or hyper-spectral image “cubes” the dimension can be any number at all.

Image Dimensions Abbreviation Alternative Name
M-N-3 BSQ Band-Sequential or Band-Interleaved
3-M-N BIP Band-Interleaved-by-Pixel or Pixel-Interleaved
M-3-N BIL Band-Interleaved-by-Line or Row-Interleaved

Images are stored in one format or another to ease image manipulations. For example, the BSQ (band-sequential) format is optimal for accessing the image spatial information (XY) or color band information. The BIP (band-interleaved-by-pixel) format is optimal for accessing the image spectral (Z) information. The BIL (band-interleaved-by-line) format is a compromise format, for the most part, allowing fairly easy access to both spatial and spectral information.

Note that you can use the Transpose function to easily turn an image from one format to another.

Web Coyote's Guide to IDL Programming