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What is the band value is > 255?

I am new to GeoTIFF, I have read through the document and came to know the RGB value can be between 0-255. But while working on one of the file, I found that value is > 255 (SS 01). Any reason why it is > 255 and what is the purpose of it?

SS 01 enter image description here

SS 02 enter image description here

Vince
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Shashidhar
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1 Answers1

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GeoTIFF files don't have to represent RGB colour images. They are general data-storage rasters, and bands can contain any numerical values, including decimals, negative numbers, things bigger than 255, bigger than 10,000,000, smaller than -9999 and so on. A band could be altitude in metres.

If this file is supposed to be interpreted as an RGB image then it may be a high dynamic range RGB image, with maybe 16 bits per channel. You'll have to check the documentation for that, and then set the min/max for each of the three channels corresponding to the colours.

The scale of 0 to 255 is a common convention because 0 to 255 can be encoded in 8 binary bits which packs nicely into a byte. But that only leaves you 256 shades of each colour which might not be fine enough for some applications.

Spacedman
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  • Thank you so much. Could you please share ideal resource for understanding how geotiff viewer decide/calculate the color for a pixel.? – Shashidhar Feb 28 '24 at 04:39
  • What "geotiff viewer"? Do you mean how does QGIS display a raster? That's the raster layer symbology dialog that you have in front of you, see the QGIS help for details. – Spacedman Feb 28 '24 at 09:47