The ENVI image format is a flat-binary raster file with an accompanying ASCII header file. The data are stored as a binary stream of bytes in one of the following formats, often referred to as the interleave type:

• Band Sequential: BSQ format is the simplest format, where each line of the data is followed immediately by the next line in the same spectral band. This format is optimal for spatial (x,y) access of any part of a single spectral band.
• Band-interleaved-by-pixel: BIP format stores the first pixel for all bands in sequential order, followed by the second pixel for all bands, followed by the third pixel for all bands, and so forth, interleaved up to the number of pixels. This format provides optimum performance for spectral (z) access of the image data.
• Band-interleaved-by-line: BIL format stores the first line of the first band, followed by the first line of the second band, followed by the first line of the third band, interleaved up to the number of bands. Subsequent lines for each band are interleaved in similar fashion. This format provides a compromise in performance between spatial and spectral processing and is the recommended file format for most ENVI processing tasks.

The ENVI raster format does not support 64-bit integer (signed or unsigned) data types.