Photo quality after photoshop

[Kelha]

Could you please tell me the facts on dpi while editing in Photoshop. I sometimes go back to a phot several times and change the "look". Does it actually decrease the image quality everytime you mess with it?

 

[JDP]

Opening and closing JPEG files will only really effect quality if you change the 'quality level' of the jpeg, no matter what every other person thinks.

Compression is compression - it's very hard to compress something thats been compressed.

Take an mp3, now create a .zip file containing only the mp3. Notice something? Right, it's not much smaller - because the mp3 is already compressed.

 

[Arch]

It has never been an issue of opening and closing a jpeg..... that doesn't effect the image anyway. Its re-saving the jpeg that causes loss of information.... and yes it will effect the image quality if done repeatedly.
There are many things that contribute towards this info loss.... for example using brightness/contrast heavily will reduce tonal information and when re-saved will cause jpeg artifacts.... reducing the image size but also compromising quality.