The difficulity of this is blowing me away.
A bitmap is rectangular. However, in many cases the actual bitmap is irregular and the pixels in the rectangle that are not part of the drawing are set to transparent. With the transparent pixels this allows the icons on your desktop to have a non rectangular shape and to go on top of your desktop. Those icons are actually square bitmaps, but with transparent pixels.
In the old days this was handled with 8-bit GIF files where a pixel could be 100% transparent or could be a color in the bitmap. But in today's world of high-res monitors and 24-bit color this does not work well. When you see an icon with a rough edge, you are seeing one where it has just this on/off transparency mode.
About 10 years ago the PNG bitmap format was created and it has a 32-bit mode where the transparency, or alpha channel has 8-bits or 256 values. So each pixel has 24-bits of color and 8-bits of alpha.
A program then blends the underlying color and the bitmap color based on the alpha channel. A value of 100% and the final color is the bitmap color. A value of 0 and the bitmap color is ignored. A value of 50% and they are blended equally.
Ok, so piece of cake. Simple concept. Well supported output format. When a graphic artist creates an image in PhotoShop (.psd file), they can just render it to a 32-bit PNG file. Artists for 2-D PC games do this all the time.
But... but...
In the last 2 months we have asked 6 different graphic artists to do this - and they have all been incapable of doing so. And what has really blown me away is that they have not really even understood the concept - to the extent that some send an 8-bit GIF file and are apparently unaware that they have dropped from 24-bit color to 8-bit color.
Maybe I'm expecting too much but I figure artists making a living creating bitmaps for the web would be capable of creating 32-bit PNG files. Because for irregular bitmaps, that is the only way they should be rendered now.
ps - If anyone knows of a url that is a tutorial for doing this in PhotoShop, please post here because there are apparently a large number of graphic artists that need to know how to do this.