How much resolution is optimum for images?

[toplisek]

I would like to do images on internet with good quality but best possible optimised resolution. Can you advise me what should be?

[drallab]

Good quality print (catalogs, magazines, etc) images are usually around 300dpi.

Web is set to 72dpi.

Optimization is personal taste. jpgs, gifs, pngs, etc can be optimized to load quick on a page; however, they may not look as good. The key is to get them to look good without causing the file size to be large causing the page to load slower.

I only use PhotoShop for images, so I don't know how the other image programs do it, but PhotoShop has a good optimization screen on the "Save for Web" option.

[felgall]

The dpi doesn't really matter for the web. It is the overall image size in pixels that is what is significant since all images are displayed at the default resolution anywhay unless you resize the image in which case the higher resolution is wasted.

[Kor]

I would rather say that neither dpi, nor the size matters. Well, the size is important, of course (but you do can not choose your size, because the design will impose a certain size), but the most important is the optimization ratio when saving for web. It depends on the needs. For a medium quality, JPG files should be optimized no higher than 50% quality, and GIF no higher than 64 colors. Rememebr, either, than transparent GIF is heavier than the same non-transparent one.

The dpi is not so important as nomater the genuine picture's dpi, the browser will present it usually on a 72 dpi. The quality depends also on the display's resolution and frequency, of course, but even so, the 72 dpi is good enough for a web site's pictures/images

[toplisek]

Thank you for fast replies.
I have seen resolution values as ...x...
What to do in this case if I would like to do 72 dpi and which software is best to do it for internet with change of optimization ratio?

[Kor]

There are a lot of freeware or not applications (give a google) which will optimze images. As a proffesional, I use Photoshop. FireWorks is a good weapon as well (some say it optimizes better than Photoshop). But both are quite expensive... If you are only an amateur and web design is not your job, use a freeware tool.

The optimization process is a simple one. Using a certain algorithm, the application will eliminate some of the images unimportant or repeatable components untill a tolerance limit on which the image has an acceptable quality. Somehow it resembles with a compression process (ZIP, RAR, ARJ, ACE...)