Re: [CinePaint] jpg worse
Frank Peters <[email protected]>
| Newsgroups | gmane.comp.video.cinepaint.user |
|---|---|
| Message-ID | <[email protected]> |
On Fri, 14 Mar 2008 14:35:59 -0500 (CDT) Bob Friesenhahn <[email protected]> wrote: > > For natural scenes, it is difficult to find visible evidence of JPEG artifacts > for reasonable JPEG compression levels. If the image is processed several > times and saved as JPEG each time, the artifacts will become more apparent. > That is why saving to JPEG should be the last step. > JPEG, although useful, is still antiquated technology. JPEG2000 was supposed to be the new compression standard but for some reason it hasn't been widely adopted. I have compressed 48 megabyte 16-bit color files down to 2 megabytes (and still 16-bit) using JPEG2000 with no discernable loss of quality. > The biggest problems noticed with JPEG compression are for non-natural computer > renderings with sharp features such as text. > That's not really a problem. It is only a case that goes beyond the JPEG design standard. JPEG uses the discrete cosine transform on 8x8 pixel blocks of data. The assumption is that there are no sharp transitions within that 8x8 block. In the case of line drawings or text, the sharp boundaries often end up within the 8x8 block and this represents extremely high spatial frequency. During compression, the highest frequnecies are discardes leaving a very ugly mess as a result. So using JPEG on line drawings or figures, or text, implies that the user has made a poor choice of compression algorithms. Frank Peters ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/