All pending tasks and bugs related to the website.

FS#5067 - Scaled-down screenshots are larger than the original

Attached to Project: Website
Opened by Adam Olsen (Rhamphoryncus) - Thursday, 16 February 2012, 10:57 GMT
Type Bug
Category Main Website
Status New
Assigned To No-one
Operating System All
Severity Medium
Priority Normal
Reported Version 1.0
Due in Version Undecided
Due Date Undecided
Percent Complete 0%
Votes 0
Private No


Start at for example

Original: 1154x578 and 130 kB
Image page: 800x401 and 747 kB
Thumbnail: 500x250 and 287 kB

I assume what's happening is the original is 8 bit and has predictable patterns. However, when scaling down it increases colour depth and uses interpolation, resulting in many more varieties of colour with subtle variation, which PNG has much more trouble compressing.

Some experimentation with JPG in GIMP finds near-indistinguishable results even at 75 quality, so long as "1x1, 1x1, 1x1" subsampling is chosen to maintain colour of fine details. 500x250 @ 75 quality gives a 50 kB file.
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