From: Bert Douglas <bertd@xxxxxxxxxxxxx>
Subject: Re: gEDA-user: Titleblocks: unlocking and filling in.
Date: Sat, 18 Dec 2004 12:21:09 -0600
Message-ID: <41C47515.50901@xxxxxxxxxxxxx>
Charles Lepple wrote:
On Sat, 18 Dec 2004 07:26:59 -0700, Kim Lux <lux@xxxxxxxxxxxxxxxxxxx> wrote:
I guess it depends on your usage. We send CAD files created by qcad as
jpegs all the time and I've yet to have anyone complain.
JPEG is intended for use on "continuous tone" images. That is --
photographs. The heart of jpeg is the DCT (discrete cosine transform).
There is an assumption of smoothness over an 8x8 DCT cell. Computer
generated line drawings violate the basic assumption of smoothness. And
computer drawings tend to use just a few discrete colors, rather than
continuous tones, as in a photograph.
Indeed.
Remember that JPEG stands for "joint photographic expert group", whereas
PNG stands for "portable network graphics".
Computer generated images generally compress better with LZW techniques,
as used in PNG.
Computer generates images should be using LZ (Lempel-Ziv) techniques, where
LZW (Lempel-Ziv-Welch) is a particular kind which has fallen out of fashion.
PNG EXPLICITLY does not use LZW, it uses good old LZ77 as being used by GZIP.
JPEG is lossy and produces an approximation of the original photograph.
PNG is lossless and preserves all details of the original graphic.
Indeed. For CAD stuff PNG is the choice.
BTW. TIFF is not a compression method, it is rather a unified format for a
set of very different compression methods.
Cheers,
Magnus