I have various scanned images in different file formats (jpg, tiff, png) and I need to georeference, clip and export those images.

As a result I need to have a 8 bit png file with transparacy (the clipped areas) on index value 255. I'm currently using ArcGIS but have QGIS and ArcGIS Pro available, but I'm somewhat struggling to accomplish this task. The 'errors' are ranging from completely black images outside of ArcGIS, having transparency for specific colors in the whole picture or having no 8 bit at all.

Could someone describe a workflow GUI- or script-based, preferably in ArcGIS but QGIS or ArcGIS Pro would be possible too.

  • The output file has to be in png-8 format. I tried different methods on how to accomplish this, for example working in ArcGIS raster format and export to png in the end or work with a png file through the whole process. Nothing really worked for me. – aldec May 3 '18 at 10:26
  • This might help: gis.stackexchange.com/questions/71973/… – BERA May 3 '18 at 10:29
  • Thank you for the link but unfortunately I don't have a general problem with exporting transparent png. Reducing the raster file to 256 colors and setting the transparancy value to the last index value of 255 is not working or results in unwanted ... results. – aldec May 3 '18 at 10:37
  • Now I have a png-8 and the NoData values from the clipped areas are on my index value 255 so this value is empty. There's now a transparancy for those clipped areas but outside of ArcGIS this areas turn out black and not transparent. So there's a difference between NoData and transparancy. Is there a way to turn the NoData values to transparent values so I can use the images outside of ArcGIS? – aldec May 3 '18 at 11:19

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