Some Photoshop save for web tests
This article is an addendum to the Setting up Photoshop for web, app and iPhone development article found on Bjango.com and published by Smashing Magazine.
The original PNG-24 file. PNG-24 is a lossless format that contains 8 bits per channel and can contain an 8 bit alpha mask (meaning images can smoothly blend into the whatever is beneath them).
The original PNG file was opened in Photoshop, then saved as a GIF with 128 colors. Close inspection reveals that some of the smooth gradients are stepped a little, but the flat blocks of color remain identical to the original PNG. The alpha mask has been made 1-bit, which in this case yields no change.
The original PNG file was opened in Photoshop, then saved as a JPEG with quality set to 30% (very low). Sharp edges have become blurry and the image is filled with compression artefacts (these look like noise and usualy form around the edge of details), but the flat blocks of color remain identical to the original PNG. The alpha mask has been removed giving a white background, because JPEG images can’t have alpha masks.