Hi - firstly, apologies if the gdal-dev mailing is not the appropriate mailing list, please advise a more suitable place to post if so.
My objective is to create a hillshaded color-relief image of a DEM using commandline/programmatic means only, so the process can be automated and combined within an existing GMT/GDAL workflow. Currently, I can generate both hillshaded and color-relief rasters using gdaldem and combine them with Mapnik (using opacity) to generate a my final rendered image. However, this process will use the min-max values in the grayscale hillshaded image. However, I can achieve an improved or sharper hillshaded image when I manually use QGIS to further process the hillshaded image by: 1. Adding the hillshaded raster to QGIS, which applies by default the 'Cumulative count cut 2% - 98%' style. 2. Then export the hillshaded raster (with the cumulative count style applied) as a “Rendered Image”. I have annotated a screenshot here https://www.dropbox.com/s/ftzk7j2bmznuvjn/raster_band_rendering.png?dl=0 hopefully illustrating the 1. Improved hillshaded raster output from QGIS ('Cumulative count cut) compared with, 2. gdal+mapnik output (using min-max) So, is there an approach using gdal (or similar command-line tool/app) to achieve the “improved” hillshaded raster without the “manual” QGIS step? As I see it, my options are: 1. Use gdalinfo with the “-hist” option to export the histogram of the hillshaded raster. I guess then I could maybe calculate the 2% and 98% percentile(?) values and then manipulate the raster values using gdal_calc.py or something else. However, I’m no statistician, so hoped there would be an out of the box solution?! 2. Maybe, I could use the python api for QGIS to import the hillshade, render, style and export back out. I’m sure this is possible, but would require an additional python script. 3. Use another library or framework to achieve either of the above. I’ve researched python’s numpy library, which maybe I could do the percentage calculation directly on the raster. Again, potentially tricky learning curve there… Any help or advice would greatly appreciated. If any help, the data I’m using is here https://www.dropbox.com/s/v0peaa3rzaqbhen/raster_band_rendering.zip?dl=0 Cheers Gareth
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