thumbnail byte-larger than original

[penguin42]

Description

The thumbnail for an image I uploaded ended up bigger than the original in bytes at the same number of pixels

Steps to reproduce

• Uploaded the image that's at mxc://matrix.org/nlkUlJCMIBWDWZLKjxZYknrn (123kB)
• Download the thumbnail at mxc://matrix.org/VPkLkCQZUMycjuCrARzGbkKa (204kB)

Describe how what happens differs from what you expected.

It probably would have been better not to produce the thumbnail in the case where the result was larger. It's a good question why it's larger; both are the same res (513x405) - I think teh thumbnail added an alpha channel for no reason; but is that the reason it's so much larger?

Version information

• Homeserver: matrix.org just now

[bkil]

This is still an issue. I would like to extend the scope of this issue:

• A thumbnail should not be saved if either the filesize did not get small or if the dimensions did not get much smaller but the filesize did not get significantly smaller either (i.e., storing both the original and a 90% thumbnail having 80% of size just wastes space)
• If I upload a .webp image, it's thumbnail is created as .png, that is vastly larger if it is photographic. In such a case, it should create a thumbnail either as .webp, or in both .jpeg and .png and only store the one which got smaller (if at all). Not sure if .avif is supported, but I guess it would have the same problem.

[bkil]

See also: https://github.com/matrix-org/matrix-doc/issues/2060 https://github.com/matrix-org/matrix-doc/pull/2068

[bkil]

See also: https://github.com/matrix-org/synapse/issues/4724

[DMRobertson]

• If I upload a .webp image, it's thumbnail is created as .png, that is vastly larger if it is photographic. In such a case, it should create a thumbnail either as .webp, or in both .jpeg and .png and only store the one which got smaller (if at all). Not sure if .avif is supported, but I guess it would have the same problem.

7586 made it so that thumbnails of WEBP images are JPEGs.