File format

Description of hyperspectral file format

This document contains a short description of the default file format that Prediktera Evince and Breeze software use to save and load hyper/multi-spectral data cubes.

The format has its origin from a format called ENVI, but only a part of that format is required.

The format consists of two files. One header file with the extension .hdr and one binary file with the extension .raw. For example: measurement.hdr and measurement.raw.

Header file specification

The required parts that must be in the header file are specified below:

• description

  • Description of the header file.

• file type

  • Should always be ENVI.

• interleave

  • Refers to whether the data are BSQ, BIP, or BIL (default).

• samples

  • The number of samples (pixels) per image line for each band.

• lines

  • The number of lines per image for each band

• bands

  • The number of bands per image file.

• default bands

  • Band Index for Red, Green and Blue default bands, used for visualizations.

• header offset

  • Offset in bytes if raw file contains binary header

• data type

  • Valid data type representation:

• byte order

  • The order of the bytes in integer, long integer, 64-bit integer, unsigned 64-bit integer, floating point, double precision, and complex data types. Use one of the following:

• errors

  • Should be {none}

  • This field will be ignored in Breeze

• Wavelength

  • Lists the center wavelength values of each band in an image.

Example of header file

The Wavelength entry has been truncated for brevity.

ENVI
description = { Exported from Breeze. Converted to Reflectance
 origfile = C:\Users\oskar\Downloads\mica_hyspex\Box 128_ref.raw }
file type = ENVI

interleave = BIL
samples = 867
lines   = 384
bands   = 288
default bands = {50, 130, 220}
header offset = 0
data type = 4
byte order = 0

errors = {none}

Wavelength = {
952.7185146625646,
958.163523875658,
963.6085330887516,
969.0535423018451,
974.4985515149386,
979.9435607280323,
985.3885699411258,
....
2482.7661035418473,
2488.2111127549406,
2493.6561219680343,
2499.101131181128,
2504.5461403942213,
2509.9911496073146,
2515.4361588204083
}

Binary file specification

The binary file format is written using one of the data types specified in the header file. How the data is stored is depending on the interleave flag. Prediktera uses the interleave BIL as default which stores one frame (samples * bands) after each other (lines).

For more information see official ENVI-format for additional information:

• https://www.l3harrisgeospatial.com/docs/enviheaderfiles.html

• https://www.l3harrisgeospatial.com/docs/enviimagefiles.html