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From: jaapv@accucx.cc.ruu.nl (Jaap Verhage)
Newsgroups: comp.graphics
Subject: Re: Alchemy on PC (JPEG compression): some findings
Message-ID: <1126@accucx.cc.ruu.nl>
Date: 27 Jan 91 16:34:09 GMT
References: <1115@accucx.cc.ruu.nl>
Reply-To: jaapv@accucx.UUCP (Jaap Verhage)
Organization: Academic Computer Centre Utrecht, The Netherlands
Lines: 34

A while ago, I posted some of my findings with Alchemy, notably
compressing existing GIF files with various quality settings, then
decompressing them and comparing the results with the originals.
Results were mediocre to bad.
Several people reacted to this, writing that starting out with GIFs
was not the way to do this. I agree. So, I then took a 24-bit Targa
file and 1) converted it directly into GIF with Piclab, in order to
be able to view it; 2) converted it directly into GIF with Alchemy;
3) compressed it, using various quality settings, then decompressed
the resulting images back into GIFs.
Findings were as follows:
1) the best direct conversion Targa->GIF was done by Piclab with
dithering off. Alchemy was not bad, but just not as good with
dithering off. With dithering on, Alchemy delivered a bit better
than Piclab. However, I *hate* this dithering: spurious dots all
over the place.
2) GIFs resulting from compressed Targa-images were bad, period. No
amount of dithering on/off or quality setting would help. I've
heard that version 1.1 of Alchemy contains a bug when decompressing
a .JPG file; it should be fixed in 1.3. Well, I believe it's time
the original authors posted this version as an evaluation copy. You
don't think I'll even *think* of registering on the basis of a
1) crippled, 2) buggy version, do you?
3) As things now stand, Alchemy performs badly for me. I'll feed it
down the drain and wait with JPEG compression until Tom Lane's
group comes out with something. In the meantime, I strongly suggest
that, if images are being posted to whatever newsgroup, they be GIF
files and not JPEG compressed ones. I'm *not* impressed with what
I've seen up till now.
-- 
Regards, Jaap.

Jaap Verhage, Academic Computer Centre, State University at Utrecht, Holland.
jaapv@cc.ruu.nl      +<-*|*->+      I claim *every*thing and speak for myself