Going ping! The virtues of the PNG format (page 2)
In these days of Broadband connections that disadvantage is not one that lays heavy with me, and those advantages are mighty appealing enough to make PNG is my first-choice for distributing my illustrations.
lossless compression & a full colour deck
Unlike a JPEG, there is no quality lost with compression. And if it is re-saved as a PNG no deterioration will occur unlike a re-saved JPEG which will get progressively worse with each re-save as the compression is re-applied. A GIF is lossless too, but that format is woefully let down by a restricted colour palette which can have dire consequences for any image that is not composed of simple flat colours. Combining transparency with a full colour palette has PNG sink a GIF when image transparency is required, as is the case for illustrations designed to sit upon a background image such as when suppling an image as a PSP tube or logo intended to sit over a site background colour. PNG's transparency is also superior to GIF's due to support for Alpha transparency.
Alpha or partial transparency
Alpha transparency refers to the ability to make pixels partially transparent as opposed to either transparent or not transparent. Consider an image designed to sit upon a page where it is desired that the existing background colour or image should be visible through the "blank" parts of the designed image, like the one below.
As you can see, the same PNG image placed on different coloured backgrounds has been made transparent so that the background colours show through. Rather than a colour it could just as easily be another image used underneath as a background. The bottom portion of the image has been made partially transparent as a gradient leading upwards.
Now consider the same image saved as a GIF.
With no support for partial transparency a halo of white pixels have formed around the edges of some parts of the image and the gradient transparency has been rendered white. Which format would you choose?
So there you have it, I'm done extolling the virtues of PNG. And now you know why I've sent your image in that format.