Hello!

I have a four band raster, which is RGB raster with transparency (alpha)
channel. In raster calculator they are listed as:
"bbb@1"
"bbb@2"
"bbb@3"
"bbb@4"

I'd like to change the values of cells in "bbb@4" channel (the alpha
channel) in the following way:
if value of the cell is smaller than 255, change it to 0
if it is 255, leave it unchanged

I do not want to change values of other channels.
And as a result, i'd like to have also a 4-band raster.

Would someone help me to create a rater calculator expression to get desired
result?

Darek Bobak



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