Hey Benedict, maybe this isn't relevant to you anymore, but I stumbled upon your question while having the same issue (ArcGIS 10.4). It looks like ArcMap, as well as ArcCatalog and ArcScene are interpreting your image as data and trying to improve the symbology by applying a "Stretch" (for me it was "Percent Clip"). Set it to "None" and it should look the same as in Windows Photo Viewer. That is what worked out for me in the end. Hoped it helps. Cheers, Markus
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