ellow,
AstAMI......as a gfxer am still learning, am still new & need some advice in GFX...my prob. is on how to save or make my file/work clear & quality....need to know what is the diff. of the jpeg, png,tiff etc......whats the usual files sizes, format or type in making good & quality gfx.....hope i can gain & in the future share what ive learned
...thanX
akil X

Are you french akil?
because ami means friend so AstAMI means asta-friend to me ;)

Anyway to answer your question.

Jpeg compression works like a mosaic. If you lower the quality too much artifacts will appear on your picture. You can choose the compression ratio in photoshop when saving as jpeg. The more you compress, the file will be lighter but won't have a lot of quality. If you don't compress a lot the file will be heavier but won't have artifact (good quality). Jpeg doesn't support transparency. It will merge all your photoshop layers.

Png produce heavy files but with good quality and support transparency. It will merge all your photoshop layers tough.

Tiff produce heavier files but with good quality, support transparency and keeps your photoshop layers separated if you wish.

Depending on your needs you will choose different type of compression. But most of the time I save as jpeg with the best quality for my artwork.

thanX bro.....no am not french....AstAMI is an acroname i use means AstafAMIly...having difficulty w/files & cs4! i work better w/cs3.....still learning thanX

I usually work in png, for quality and transparency, though I would use jpeg if I was making a wallpaper for example, when working on things like sig and avatars the difference between jpeg and png is tiny, and will mostly be affected by how many colours you use. Gif is the only practical option for animations, but you rarely use it for anything else, as it is pretty bad quality, but you do sometimes use it when making websites for little buttons due to good compression and 1 bit transparency.
Tif is rarely used now, as png has overtaken it. Some designers still use tif for stock images, but this is mostly out of habit.

many thanX my fellow asta gfxers.....my progress is a big help from you.