Re: [stella] Homebrew-Homepage-Screenshots

Subject: Re: [stella] Homebrew-Homepage-Screenshots
From: "Andrew Davie" <adavie@xxxxxxxxxxxxx>
Date: Mon, 12 Nov 2001 16:02:50 +1100
> Actually, GIF is in fact lossy!  GIFs can only have a 256 color palette,
> so the image is first quantized lossily to 256 colors, then lossless LZW
> compression is applied.  PNG is the same, except it uses a 16-bit palette.

This is obfusticating, IMHO.  There are *NO* bitmap image formats which are
lossless if you argue like this.   And don't try to suggest that
vector-based images could be lossless, because there's an inherent inability
for computers to precisely represent all real numbers.  Even
"Photographic-quality" images are STILL lossy, no matter what format you
choose to save them, as there are only a distinct number of colours
available.  So, IMHO, that sort of argument is missing the point entirely.

GIF image format is *not* inherently lossy.  The fact that it's limited to
256-colour images maximum is neither here nor there.  GIF is lossless, in
that it does not mangle your source image when it compresses the data.  All
of the original 16 or 256-colour bitmap data can be reclaimed intact.  The
distinction is between the capabilities of the image format to store a
suitable image in a lossless way, or not.  GIF *does* represent the images
it is designed for (ie: <= 256 colours) in a lossless fashion.  Likewise,
PNG and BMP can similarly store higher (and lower) colour-depth images in a
lossless fashion.  AFAIK, it is not possible to guarantee lossless
compression with JPG.

And one final point, PNG has variable colour depth - and be careful... there
is a distinct difference between 16-bit colour depth and a 16-bit palette.
I use PNG wherever possible - it's supported by browsers, and is in common
use nowdays.

Andrew Davie, TwoHeaded Software

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