I created an RGB Uint16 composite raster in QGIS . These are band designations:

  • Band 1 - blue
  • Band 2 - green
  • Band 3 - red

When i query value of a pixel that appears green - it shows (B3: 668, B2: 983, B1: 1007). Since the pixel is green, I expected DN in the green band to be the highest, although this is not the case.

Why is that?

The raster is stretched and clipped using 2 - 98% cumulative count, although the values queried are raw DNs.

enter image description here

  • 1
    Will you check the Layer property > Symbology, to see the setting of each band (min, max)? These min and max might be simply reflecting the range of your input data. – Kazuhito Feb 22 '19 at 13:31

As you mention in your PS, the values returnedby your query are raw values. On the display, the RGB values are stretched between 0 and 255 (on a 3x8bit monitor) depending on the distribution of the raw values. So, for intance, if the range values are 0-10000 for red, 0-1000 for green and 0-10000 for blue, the min-max contrast stretch would be like R(display)26, G(display)253 and B(display) 17 , which is green on display.

  • Thank you! So it came down to min and max values on a stretched scale. The values were: Scale: R (400 - 1434), G (616 - 1404), B (873 - 1524), the pixel values were initial R (668), G (983), B (1007). Then I zeroed the min value for each channel and subtracted it from all values. Scale then became R (0 - 1034), G (0 - 788), B (0 - 651) and R (268), G (367), B (134) for pixel. Then I rescaled everything to 8 bit, which produced Scale R (0 - 255), G (0 - 255), B (0 - 255) and Pixel: R (66), G (119), B (52). That gave me exactly the same color as on the screen – Basile Feb 22 '19 at 20:06

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