If you screenshot computer/phone interfaces (text, buttons, lots of flat colors with adjacent pixels the exact same color), the default PNG algorithm does a great job of keeping the file size small. If you screenshot a photograph, though, the PNG algorithm makes the file size huge, because it's just really poorly optimized for re-encoding images that are already JPG.

[–] NateNate60@lemmy.world 1 points 1 week ago* (last edited 1 week ago) (1 children)

I took a screenshot of this page

(Screenshot removed because it takes forever to load and is not interesting enough to waste bandwidth on)

I am connected to a 4K monitor and this picture is also at 3775 × 2119. The total file size:

12.1 MB

[–] GamingChairModel@lemmy.world 1 points 1 week ago

Still a pretty limited palette, everyone wearing the same color shirts.

PNG tends to fail hard with textures. For example, my preferred theme in my chess app, which has some wood grain textures, generates huge screenshot file sizes (2MB), whereas the default might be less than 10% as large. Similarly, when I screenshot this image the file size jumps to 2MB for a 0.8 megapixel image.

Rendered textured scenes could easily overload the PNG compression algorithm to where they're huge, and if Discord is historically associated with gaming, one can imagine certain video game screenshots blasting past that 40mb limit.