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In QGIS when defined a singleband pseudocolor symbology, the interpolation between 2 steps acts in a way I can't seem to understand.

Take for example step 1 and step 2: enter image description here

  • Value 0,0000002 is defined color #000000.
  • Value 3,3752645 is defined color #010204.

On the raster a pixel with value 0.0759562 is rendered as color #000000.

The expectation would be that the value 0.0759562 would be interpolated between step 1 and step 2. The color to expect with linear interpolation would be #0005CE.

Is the interpolation between steps acting different the expected?

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You have to consider the interpolation is done for each value of your hexadecimal rgb-triplet separately, in your example:

r = #01, g = #02, b = #04.

Calculate the ratio of 0.0759562 / 3.3752645 = 0.02252 approx. and multiply it with each of the rgb values separalety gives you

r: #01 * 0.02252 = #00 (rounded)
g: #02 * 0.02252 = #00 (rounded)
b: #04 * 0.02252 = #00 (rounded)

or written as a hex triplet: #000000 according to what you have observed.

The slight misunderstanding ist to consider the whole hexadecimal number #010204 (66052 in decimal) and calculate the portion of it with the ratio given above (66052 * 0.02252 = 1487 approx. = #0005CF according to your expectation).

This can easy be proven visually because #0005CF is some blueish tone that has clearly no place in between your two edge colors:

enter image description here

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  • Thank you for clarifying this. The new color having no place between the two edge colours is of no problem. What I am trying to achieve is to encode the values between min/max into RGB colours so to recalculate the value based on a hex triplet. Is this safe to do?
    – Hoetmaaiers
    Aug 22, 2022 at 7:36
  • The RGB triplet to pixel value idea leans on this shader idea: observablehq.com/@sw1227/decoding-png-elevation-tile. With the difference being the dynamic min/max value and thus dependency on the interpolation between bins I think.
    – Hoetmaaiers
    Aug 22, 2022 at 7:41

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