There is a "quality" setting you (are supposed to) use when saving out a JPG, that defines how much detail will be lost during compression. The lower the quality, the shittier the resulting picture.

What is likely happening, however, is that site after site after site adding their shitty little banner/tag to pictures in addition to setting the quality slider too low. When you do that, image artifacts - created by setting the slider too low - build upon earlier image artifacts created by other sites.

It's really fucking stupid because the file size savings between 50% quality and 90% quality is only about 10%. Why not just set it to 90% and avoid the worst of the artifacting? At higher quality levels the artifacts that do build up are so small as to be only visible under magnification.

>the file size savings between 50% quality and 90% quality is only about 10%.

I call bullshit on this.
Test case: JPEG Image from my camera.
90% quality: 7021 kB
50% quality 1676 kB

Test case: Random porn image
90% quality: 134 kB
50% quality: 50.4 kB

That's roughly 250% to 400% increase, going from 50% quality to 90% quality.

You're right about multiple re-encodings of the same image at shitty quality levels leading to exceptionally crappy image quality though.

>if I save a picture from 7chan here, it doesn't get garbled up, right?
Saving a JPEG means copying it - no quality loss. On the other hand, when you take a JPEG, open it in Gimp/Photoshop and then export to JPEG you'll be inserting more noise in an image that already contains noise, i.e.:
I = Image with no quality loss
convert to JPEG: JPEG1 = I + noise
convert it again: JPEG2 = JPEG1 + noise = I + noise + noise

>On the other hand, when you take a JPEG, open it in Gimp/Photoshop and then export to JPEG you'll be inserting more noise in an image that already contains noise

It should be noted that it isn't just Gimp/PS that does it when exporting, ANY image software that re-saves the image will do this. If you opened it in MSPaint and saved and exited without editing anything you would introduce artefacts.

>>19758
The difference between file sizes is entirely based on the actual composition of the photo itself. Images with large blocks of uniform color, for instance, compress far better than images with lots of small detail, and this definitely carries over to the size of the resulting file. That being said, it was a gross oversimplification on my part, since every image is going to compress different. I have images, admitted small resolution images with lots of detail, that don't vary much between 90% and 50%. They look like shit at 50%, of course.

>>19760
While true, with higher the quality settings, the less noticeable the noise will be (because the noise gets confined to ever-smaller blocks as the slider rises). 90% of the shitty images on the internet could still have been crystal clear if they hadn't left the quality slider at 50% every fucking time they re-saved the image.

>>19762
>19760R
No significant disagreements, was just attempting to clarify that it wasn't an exclusive effect of exporting in GIMP/PS.

File 135690397367.png - (23.20KB , 420x450 , jpg_vs_png2.png )

So it all boils down to: Fuck sites that put watermarks on images?

>>19764
Agreed, it's definitely not unique to GIMP or PS or (insert name of graphic utility here). This issue with JPGs is caused by the lossy nature of the JPEG compression standard.

>>19768
At least those that leave the quality slider in the middle, or don't adjust it at all. Most of them are using a CLI-based utility to insert an overlay on top of the image, and instead of passing a (for example) -quality 9 argument when saving they're leaving it at the default, which typically means 5.

Unfortunately, most porn sites, at least the ones that re-post work from other sites, aren't run by the brightest bulbs.

saged for not adding anything relevant to a resolved conversation.