Did some real testings now. For games that make screenshots go over 45kb, it's hardly possible to get a jpeg with no visible loss under the site's limit. If it's not some exceptional case (like png being smaller than the best sub 45kb jpeg, or best jpeg being 40kb), it'd be best to just pick the first one that's below the limit, since in most cases there will already be compression artifacts there.
However, to know which one fits best, you'd need to create jpegs with quality step of 1 (down to some 70). Here are the images that
I would use for publication. Format:
Game: quality / jpeg size in bytes.
Comment
PNG JPEG images
Abe: 94 / 44,685.
"0" at the monitor starts fading at lower qualities.
F-Zero: 92 / 48,624.
Artifacts at the road stripes are already present on the first sub 50kb jpeg.
Pinball: 76 / 50,578 (woops).
No comments.
Luigi 1: 98 / 40,649.
Artifacts appear around the ligntning if you go under 98, but 98 is already small enough.
Luigi 2: 97 / 42,458.
BG on the right gets blurred and blocked under 97.
Crash: 94 / 47,341.
Hard to see, but artifacts around Crash and on the sky.
So here are the steps that I'd be using when making a publication screenshot for such a game:
1. Check the compressed PNG size.
If sub 45kb, publish it. If it's bigger:
2. Make a bunch of jpegs from 99 to 70, with quality step of 1. Use the above batch for that.
3. Throw away everything above 45kb.
4. Compare the best one of the rest with the source.
If there are artifacts already, publish. Otherwise:
5. Go through all the smaller jpegs to see where artifacts start appearing.
6. Pick the one right before the first artifacted one. Publish.
EDIT: Well, the limit is actually 45kb. Whatever.
