Summary: Professionally shot JPEG images uploaded to the Commons are over-sharpened in both thumbnail and all resized versions, often creating a horribly over-processed image when no additional work was needed.
This is an issue affecting select images, typically those taken by professional photographers (that Wikimedia sorely needs more of), that are pin-sharp, perfectly-focused and with strong depth of field. Such photographers are liable to already upload their images perfectly, so additional processing - especially so severe - is frustrating.
ImageMagick, to my understanding, sharpens images when generating thumbnails and is the cause of this issue. It does not do this to PNG images, and as such a workaround has been to use PNG, which is recommended in the documentation for print quality photographs regardless. However, not all are keen on use of PNG, so a solution would be preferred.
This is a particular issue as it affects the best photographs, and may put off professional photographers from contributing. Wikimedia UK has recently campaigned for those capable of professional images to get involved, and such barriers are unfortunate.
Possible solutions include:
- Introducing options for advanced users that allow them to stipulate no-sharpening (and perhaps also a low-sharpening option), maybe restricted to those activating it in settings to avoid misuse. CMS such as WordPress support such parameters and it would most likely involve informing ImageMagick of the way to handle the specific image on upload. This is the option I prefer.
- Looking at changing the sharpening algorithm to reduce the amount. This is my lesser preferred option as some images do not need any additional work, often the very best on the Commons, and the default sharpening does help blurry bridge camera and mobile phone photographs.