Re: TECH: PNG files

Different tools for different tasks.  PNG and JPEG are apples and
oranges -- JPEG is good for lossy compression of photograph-like
images.  PNG uses lossless compression, and therefore achieves high
compression rates only for images which are eminently compressible --
i.e. ones with areas of truly flat color, with sharp edges between
them.  I would think that fonts would be a good example of very
PNGable images.

If loss is tolerable and the image is photographic, JPEG is ideal.
If the image is not photographic -- if it contains areas of flat color
with sharp edges -- you will likely get "JPEG Jaggies" -- ugly
artifacts in the final product.  (You will also start to notice these
even in photographs if you choose very high JPEG compression rates.)

PNG is really not a competitor to JPEG, but to GIF, which is burdened
with a patented and non-free compression scheme and a limit of 256
colors in the image.  PNG fixes these problems and adds a lot of extra
functionality; its only disadvantage is that it is not yet as widely
supported as GIF.  But alas, that is a real disadvantage.  Maybe it
won't be in a couple years, but right now lack of browser support for
PNG in older browsers is a real issue.

---------------------------------------------------------------
Ed doesn't know everything, but he hasn't figured that out yet.
Please break it to him gently.              edheil@postmark.net
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Paul Bennett wrote:

> On a related note, unless your images are very small, or are absolutely
> dependent on individual pixel values, I'd advocate JPG over PNG any day of
the
> week.  (Asbestos suit at the ready! :-)