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ReadImage – Spectral Band Arguments
Hoku deals with three kinds of images: monochrome, color and multispectral. A monochrome image has one spectral band. A color image has three: red, green and blue. A multispectral image has more than one band; it could have tens of bands, or even hundreds.
If an image has N spectral bands, they are numbered 0 to N-1. A color image has 3 bands: 0 is red, 1 is green and 2 is blue.
The “bands” argument tells ReadImage which bands to read and include in the image it outputs. You are warned if you ask for a band number that does not exist in the input image.
Writing band numbers
| You write | Meaning | Example |
|---|---|---|
| single numbers, separated by spaces or semicolons | exactly those bands | 2 4 5 8 |
start:stop | bands start to stop, and all the bands in between | 0:2 reads bands 0, 1 and 2 |
start+stop | bands start to stop, averaged together into one output band | 21+40 |
You can combine them. On a hyperspectral image, 21:40;55;61:70 reads 31 bands, while 21+40;55;61+70 outputs only 3 bands, two of which are averages. A single range uses either : or +, not both.
The same band syntax works in Crop.