Posted Sun Aug 14, 2005 2:19PM
I stumbled across a link today trying to find a way to explain compression artifacts to a family member and I thought that it would be of benefit to alot of folks here on iStock, since in the newby area questions, and sometimes a rejection complaint, pops up in the forums asking what the heck is compression artifacts.
Rather than give a lengthy dialogue about the technical reasons behind it and having people running for the asprin from the headache that goes with all the technical mumbo jumbo sometimes it is just easier to "show and tell". This is a demo that let's you add compression to an image:
You can add different levels of compression to the sample images, different types as well, but it gives you somewhat of an idea of where to look for these compression artifacts and maybe compare it to your own. And dang it there is some fun to screwing up an image and not having to feel bad about it.
**Just a note, in helping you see mild compression, it tends to first start appearing where colors transition like from a light to a dark color. A good example would be tree limbs against a light sky or even eyelashes against the color of the skin. It can also be noticed in large solid tones that should be even but appear to have "specs" peppered throughout, such as sky or fields of grass. It appears like little globs or blocks, sometimes sharp and sometimes a little blurry.
Now if you want a super long, super detailed drawn out explanation with examples and covering just about every area of data compression in images then you might want to check out this link:
Holy Wiki-Compression Batman!
So have some fun reading up and playing with that little demo
(Edited on 2005-08-14 14:35:53 by kcline)
Posted Sun Aug 14, 2005 2:21PM
awesome stuff, thanx for the links.
Posted Mon Aug 15, 2005 7:55AM
Interesting. Thanks for the link
I still have trouble differentiating between compression artifacts and sharpening artifacts. I recently shot some raw photos and converted them using the lowest possible sharpening in Rawshooter and they look like they have been sprinkled with glitter!