WriteImage

WriteImage can write in any of 6 image formats, Tiff, Envi, Jpeg, Png, Bmp, and Text files. The last format, Text, produces a simple text file, with a format that is unique to Hoku. The extensions of “.tif”, “.hdr”, “.jpg”, “.png”, “.bmp”, “.txt” are required in the names. Tiff is an archival format. ENVI is good for computations, and JPEG should be used only for display.

Jpeg files use lossy compression. The “quality” parameter varies between 0.0 and 1.0. Zero being the lowest quality and smallest file. Unity being the highest quality and largest file.

The Tiff and Envi formats can handle 8- or 16-bit integers, or a 32- or 64-bit floating point values. The other three, Jpeg, Png, and Bmp can only output 8-bit integer, monochrome or color images.

Tiff files default to writing uncompressed, but two lossless compression options are available, LZW and Deflate. The best compression is achieved with Deflate and Differencing.

ENVI files consist of a header file (.hdr) and a data file. The “interleave” parameter specifies how to write out the data. BSQ is best for when you want to look at one band at a time. BIP lets you look at all bands at once, as in a spectrum. BIL is a compromise in access speed.