Hi all! I'm having trouble getting gdaldem to work the way I believe it's supposed to. In particular I have given it a single-band uint8 GeoTIFF and tried to map the values to RGB bands via a colormap using exact matching, but the resulting GeoTIFF is invariably all zeroes (as if there were no matches). Using -nearest_color_entry or not specifying -exact_color_entry yields the expected results, but I only want exact matches. I have tried specifying values to match as both floats (0.0, 1.0, etc.) and ints (0, 1, etc.). Adding an alpha channel makes no difference in this sense. Am I doing something wrong, or is there an issue with gdaldem? Here are the commands I used, and a link to the files in question:
gdaldem color-relief -co COMPRESS=DEFLATE -co TILED=YES -co BLOCKXSIZE=256 -co BLOCKYSIZE=256 -co SPARSE_OK=TRUE -co INTERLEAVE=BAND -exact_color_entry -alpha foo.tif colormap.txt exact_foo_with_alpha.tif gdaldem color-relief -co COMPRESS=DEFLATE -co TILED=YES -co BLOCKXSIZE=256 -co BLOCKYSIZE=256 -co SPARSE_OK=TRUE -co INTERLEAVE=BAND -nearest_color_entry -alpha foo.tif colormap.txt nearest_foo_with_alpha.tif gdaldem color-relief -co COMPRESS=DEFLATE -co TILED=YES -co BLOCKXSIZE=256 -co BLOCKYSIZE=256 -co SPARSE_OK=TRUE -co INTERLEAVE=BAND -alpha foo.tif colormap.txt gradient_foo_with_alpha.tif https://drive.google.com/drive/folders/17q3zQAcOqPTo4f8-swWEgrpQ9sfufasR?usp=share_link These commands were performed with GDAL 3.9.1 installed on MacOS/ARM via Homebrew, though the problem also occurs in our AMD64 AWS instances running Linux and GDAL 3.8.4 with the official Docker images as a base. Thanks for any help! Daniel Mannarino
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