From: Bert Douglas <[EMAIL PROTECTED]> Subject: Re: gEDA-user: Titleblocks: unlocking and filling in. Date: Sat, 18 Dec 2004 12:21:09 -0600 Message-ID: <[EMAIL PROTECTED]>
> Charles Lepple wrote: > > On Sat, 18 Dec 2004 07:26:59 -0700, Kim Lux <[EMAIL PROTECTED]> 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
