Screenshots PNG vs JPG, some facts need to be checked

[kurzih 56]

I got bumped from a related thread since this was not really in the center of that discussion:

Just recently I'm seeing moderator changes/replacements from native PNG resolution to slightly upscaled JPG screenshots - with older games like from the Spectrum ZX etc., claiming that it's "better quality" making a bigger sized JPG screenshot. I think that is misleading and a bad mistake to approve those changes/replacements. Why is that? Because JPG files when saved (or should I say auto-scaled by  Launchbox/BigBox) into a different resolution will add grain/noise especially around texts etc.

PNG has lossless data compression and looks great auto-scaled in HD of whatever resolution (smaller or bigger) and it will also preserve the colours. No user should need to make screenshot image bigger than what they are in their native resolution if they are saved in PNG. I don't mind if someone upscales a PNG image (even if it's not really of any use), but changing perfectly fine PNG screenshot files into JPG is making the quality worse, not better - especially with BigBox.

I'm sure there's people here in this forum who are very familiar with these formats and I'm quite sure they would voice it for PNG as a preferred format for screenshots. And anyone can google more about the benefits of PNG and problems with JPG for screenshots or in general, like https://en.wikipedia.org/wiki/Portable_Network_Graphics.

Even if the database allows both JPG and PNG image file formats, I think we should focus on what's best for what image type and avoid any false moderation claims and stop replacing perfectly good, already approved, native resolution PNG images.

I'm emphasizing "screenshots" here. I don't wish people to start changing Box - Front/Back / Flyers images from JPG to PNG. Since that would only fill everyone HDs. High/Maximum Quality JPG files are OK for these kind of files but are not good for screenshots (especially old games with low native resolution).

Edited November 18, 2020 by kurzih

[Belgarath 103]

100% agree. Screenshots should never ever be jpg. PNG should be pretty much the only format used for screenshots.

Upscaled png screenshots are fine as long as it's a direct multiple of it's native resolution 320x240>640x480>1280x960 etc

Scans should preferably be jpg.

[Thanatos_Prime 37]

Thanks for posting. I was debating if I was being overly harsh declining some of the ones that made the least sense. I have no problem adding jpg (if that's all you can make or get) if there are none in the DB, but deliberately replacing good PNG screenshots with questionable and only slightly larger JPG files seemed a bad move. I wish I had read this 30 minutes ago, you would have saved me some agonizing.

[Sylwahan 3]

Screenshots for older 2D games, NES/SNES/Neo Geo etc. should always use PNG in native resolution or integer scaled. The pixel graphics both look and compress better than with JPG. It's only with 3D lighting and in particular texture filtering the images become complex enough that it's worth switching over to JPG at high quality, preferably without any color subsampling (which unfortunately not all image applications have the option for.)

So for example for the dithered graphics of PSX it's still worth sticking with PNG even for 3D games for the most part—assuming the screenshots were taken with something like Mednafen without any additional texture/image filtering in the emulator— while for N64 which has texture filtering PNG starts to become a bit bloated.

I'll attach some examples.

First, Metal Slug at 304x224 native res. PNG is 29 KB, a very high quality, visually equivalent JPG is three times that at 101 KB.

Second, Metal Gear Solid at 320x240 native res. PNG 41 KB, JPG still bigger at 69 KB. You could probably get away with lowering the quality a bit here, but there would still be no benefit or point to it over PNG.

Third, Star Fox 64 at 320x240. PNG ends up a bit bigger here at 75 KB due to the texture filtering. Same quality JPG as before is now the significantly lighter option at 48 KB, though there may be some hints of compression noise if scaled up.

Now if the issue is that the native res is too small or images get too blurry when scaled up, the good news is that for this kind of graphic PNG is quite forgiving of upscaling as long as it's integer scaled/unfiltered.

The final set of images here is the same MGS screenshot but integer scaled four times to 1280x960. Despite a 400% increase in resolution the file size only increased by 70%. Meanwhile the JPG of that resolution at the same quality as before ends up at a whopping 400 KB!

tl;dr PNG is pretty much always superior, regardless of resolution, as long as there's no filtering involved in the game rendering or in the image scaling. For more complex, smoother 3D graphics from about the N64 and forward, high quality JPG is likely going to be the better option.

Edited November 23, 2020 by Sylwahan