Bad quality when I save for Web!

Zeinab,

Resolution can be worse then irrelevant.

It is the final size expressed in pixels x pixels that counts, so if you create the artwork at 500 x 500 pixels on the Artboard and export at 300 PPI you will get 2083 1/3 x 2083 1/3 px, bound to cause trouble. With 2500 x 2500 px it will be 10416 2/3 x 10416 2/3 px.

This may sound unforgivably outdated and boring, sorry.

If you wish to have PNGs (PNG24 (also (little) known as PNG32, it holds 24 bit colour and 8 bit Alpha channel (transparency)), of course) look crisp and clean, it is important to have the images in the exact desired final pixel x pixel size, forget about resolution which may actually lead to wrong sizes and hence blurriness. It is easiest and safest to work at the desired size.

A very common unsuitable way is to Export to PNG (remember to use PNG24 and use Transparency for artwork to be in front of different backgrounds) with a medium or high resolution, such as 300PPI.

To retain the clean and crisp artwork, a PNG must be created at exactly the pixel x pixel size that it is to be used for, or at sizes that are powers of 2 times as large (2, 4, 8, and so on).

For clean and crisp artwork avoid JPEG.

It is also important to have the artwork and also the Artboard placed fully within integer/whole pixel X and Y values in the Workspace. Otherwise the resulting image will become a bit wider/taller and the extension(s) will be empty and therefore be white.

Therefore, the safest way is to create the artwork at the final pixel x pixel size and use a corresponding Artboard, then either use the Legacity Save for Web (where you can look in the Image Size window for size confirmation) or Export at 72PPI. In either case, use the relevant optimization (available with both ways); it is also convenient to have 72PPI in the Effect>Document Raster Effect Settings.

If you have pure vector artwork, you can relax a bit and have the artwork/Artboard at any size (the Artboard must have the same proportions as the final image), then use the Legacity Save for Web and set either Width or Height in the Image Size and Apply (make sure the other value is also correct).

The Legacy Save for Web may be an old carthorse, but it knows its way home, even if the driver is drunk and sleeping it off in the hay in the back.

Hi. If you are exporting for web the resolution is not relevant. You need export to 2X factor at least, which means that you need export to double of size (1000px x 100px), then the web designer will use the image at 50% of the size and the quality will be better. That's because the actual resolution of monitors is high (retina display).