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Maniphest T127658

PNG thumbnails of black and white images are darker than original image
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Description

I've noticed on several black-and-white PNG images uploaded to Wikimedia Commons and English Wikipedia that the thumbnails are much darker than the original image. This can be seen in the following examples:
https://commons.wikimedia.org/wiki/File:Barry_Gibb_(Bee_Gees)_-_TopPop_1973_1_(cropped).png
https://en.wikipedia.org/wiki/File:S._G._THORELL_(Sweden).png

This seems to be related to the ImageMagick bug documented at http://www.bennadel.com/blog/2825-fixing-grayscale-png-thumbnail-images-that-come-out-too-dark-in-imagemagick-6-7-7.htm , in which case the solution was to force ImageMagick to render thumbnails as 24-bit PNGS (adding "-define png:format=png24").

Event Timeline

Ahecht created this task.Feb 21 2016, 6:33 PM
Restricted Application added subscribers: StudiesWorld, Josve05a, Steinsplitter, Aklapper. · View Herald TranscriptFeb 21 2016, 6:33 PM
Ahecht updated the task description. (Show Details)Feb 21 2016, 6:48 PM
Josve05a added projects: MediaWiki-File-management, Multimedia.Feb 21 2016, 7:22 PM
Restricted Application added a subscriber: Matanya. · View Herald TranscriptFeb 21 2016, 7:22 PM
Bawolff closed this task as a duplicate of T106516: Greyscale pngs without gAMA chunk rendered with incorrect contrast [or setting the gamma in GIMP exports to PNG].Feb 21 2016, 7:26 PM
Ahecht added a comment.Feb 21 2016, 8:27 PM

This seems to be related to the ImageMagick bug documented at http://www.bennadel.com/blog/2825-fixing-grayscale-png-thumbnail-images-that-come-out-too-dark-in-imagemagick-6-7-7.htm , in which case the solution was to force ImageMagick to render thumbnails as 24-bit PNGS (adding "-define png:format=png24").

Bawolff subscribed.Feb 21 2016, 10:19 PM
In T127658#2049950, @Ahecht wrote:

This seems to be related to the ImageMagick bug documented at http://www.bennadel.com/blog/2825-fixing-grayscale-png-thumbnail-images-that-come-out-too-dark-in-imagemagick-6-7-7.htm , in which case the solution was to force ImageMagick to render thumbnails as 24-bit PNGS (adding "-define png:format=png24").

I don't think that blogpost is correct (or at least is misinterpreting the causes). Anyways the fix is documented up above at the beginning of this bug

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