How to remove JPEG artifacts in Photoshop?
 

I stumbled upon a very nice wallpaper, but it's smothered wtih horrible artifacts. I'm pretty adept with PS, but this one has me stumped - how do I remove artifacts? Theoretically it should be simple as the drawing's got a vector-like quality, but even still, brushing over the entire thing seems to be far too much hassle...

I'm using CS2. If anyone can help, it'd be great.

I reckon you should be able to get rid of all of that using the clone stamp. It would take a bit of work though and pehaps there is a faster way, I don't know.

I'm actually considering doing a completely vector version of it (1600x1200 ftw), but that could take more time and effort than I'm prepared to waste unless someone can link me to a very detailed pen tool tutorial.

As for the clone stamp, I'd rather do something that'd affect the whole photo at once rather than having to get rid of each little artifact individually. Could work, though...

You cannot remove JPEG artifacts no more then you can improve the quality of a MP3 file. It's a lossy conversion, the lost data cannot be recovered.

Photoshop (or was it Paint Shop Pro 7.4 ?) should have a JPEG artifact removal filter but it helps only marginally.

How can you tell if a picture has jpeg artifacts?

You use your eyes.

Look at the outer edges of the objects in the wallpaper in question and you should notice that something isn't quite right.

In most circumstances, yeah, but I can easily replace what was lost in this instance considering it uses simple colours and shading along with very defined borders/contrasts between the elements in the picture.

Also, there's no such filter present in PS. :( Shame.

If you have flash, maybe try importing this image into flash and use the "Trace Bitmap" feature. Since this has mostly solid flat colors it might do a decent job with the proper settings.

Photoshop's Smart Blur filter will nuke most of those artifacts right off the bat.

Ack, beat me to it. Yeah, just apply a smidgen of blur and it'll soften the artifacts out.

It's easy. You will notice the image being broken up into various visible "squares". This is because what JPEG compression does is actually break an image up into several tiny implicit patterns, which takes up less space. The higher the compression, the simpler the patterns that are used. When the patterns are too simple to fairly represent the way all or part of the image should look, it's referred to as "JPEG artifacts".

See here for more info:
http://en.wikipedia.org/wiki/JPEG