The RasterExpressionEvaluator is a transformer that evaluates expressions on each cell in a raster, such as algebraic operations or conditional statements.
The images show Heritage Mountain Elementary School and the surrounding area in Google Earth
Port Moody, Greater Vancouver
Note that this method should be used cautiously - if there are bright areas in the image, they will reach or exceed the maximum value (255 in my example), which will make them purely white (255, 255, 255 in case of RGB24), and the information in those areas will be lost.
Most internet sources suggest the following formula for color to grayscale conversion (and many sources also mention that depending on the image it may vary):
0.2989*A + 0.5870*A + 0.1140*A
0.3333*A + 0.3333*A + 0.3333*A
but the first formula gives better contrast.
If we inspect results in Visualizer, we will see the results of the conversion:
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