On Wed, 13 Jan 1999 14:35:40 +0100 (MET), Omer Nezih GEREK
<gerek@xxxxxxxxxxxxxxx> jammed all night, and by sunrise was overheard
remarking:
> On Wed, 13 Jan 1999, Richard Ross wrote:
> > Formats such as TIFF, GIF etc use non-lossy compression, i.e. all the
> > information in the original is retained throughout the compression /
> > decompression process.
> GIF sucks. It is indeed a very lossy coder. It codes only 256 colors with
> a stupid color quantizer, therefore your image gets dithered and has the
> un-appealing look.
Well, not really. GIF is a lossless 8-bit palettized format. If you have
a program that will offer to save anything beyond an 8-bit image to GIF,
blame the program, not the GIF format. I tried this in Photoshop and
PhotoImpact -- both require ME to explicitly generate an 8-bit image
before I get to create a GIF. And it is indeed lossless -- the image I
save is exactly the image I requested to save.
GIF is primarily useful for artwork integrated into Web pages,
especially line or drawn art. And it has the advantage of maintaining
transparency if you want it. It's not suitable for good quality photo
presentation. Though I would debate that any Web-friendly format is much
good for this, if you're after art. Functionally, though, when you have
20 or 30 formats your software can write, you have to suspect that there
comes a time when you need to select the right tool for the job. When I
wrote a web site that gave a walk-through photo tour of my old house
when trying to sell it ( pretty effective -- the eventual buyers
apparently spend lots of time there with friends and family), I put up
all the (fairly small) photos in highly crunched JPEG, usually dropping
each file to around 10-15K, depending on what it looked like. The point
here was certainly illustrating the house nicely, but also making the
walk-through fast enough so that you could actually walk through it. If
folks has to wait 5 minutes to download each picture, they would have
left angry.
> > JPEG gives you nice small files for use on the web etc, but you will lose
> > information when you use it. I didn't know until recently that the process
> > is not reversible - if you save, open, save, the two saved files aren't the
> > same.... AFAIK only the JPEG and MPEG formats suffer from this.
> There was (and somehow, is) a huge research on lossy and lossless image
> compression methods. JPEG is an old standard, therefore adopted by the
> browsers.
There are certainly a variety of lossy compression algorithms; JPEG and
MPEG were the first with any sort of wide distribution. There are also
fractal and wavelet formats, which offer different properties. Wavelet
compression is gaining a reputation for delivering better quality at the
same compression rations than JPEG. A friend of mine runs Engineering at
a computer video-oriented company, and they've successfully used some
form of wavelet compression rather than MJPEG for video capture. Some of
the Vivitar digital cameras do also, and deliver more "high quality"
images in the same memory -- though evaluation of the quality is
difficult, since they also use a CMOS image sensor, not the more common
(and currently better) CCD.
Fractal compression offers the interesting property that it's inherently
scalable. So you could use it for a web page that looks nice at 640x480,
but all the better at 1280x1024, all based on the same images.
The main reason JPEG/MPEG have caught on, and others haven't, is that
the others are often quite proprietary, possibly (like GIF) covered by
someone's patents, and so fairly contrary to the nature of the Web (one
of the primary driving forces for new image compression techniques).
Also, when you have working standards like JPEG, it's virtually
impossible to convince someone like Netscape or Microsoft they need to
pay YOU money to support a superior image format.
For image archival, why not store images without compression, or both?
Especially if you're putting them on a CD, you can fit a whole roll of
film scanned at 1600x1200 on one CD, with both raw and JPEG versions if
you like, and it costs you $2.00 if you do it yourself, $10.00 if you
let folks like Mystic or Kodak do it for you.
--
Dave Haynie | V.P. Technology, Met@box Infonet, AG | http://www.metabox.de
Be Dev #2024 | NB851 Powered! | Amiga 2000, 3000, 4000, PIOS One
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