[Tig] Fwd: [CinePaint] jpg worse

Rob Lingelbach rob at colorist.org
Fri Mar 14 20:00:46 GMT 2008



Begin forwarded message:

> From: Frank Peters <frank.peters at comcast.net>
> Date: March 14, 2008 9:57:58 PM GMT+02:00
> To: CinePaint Users <cinepaint-users at lists.sourceforge.net>
> Subject: Re: [CinePaint] jpg worse
> Reply-To: CinePaint Users <cinepaint-users at lists.sourceforge.net>
>
> On Fri, 14 Mar 2008 14:35:59 -0500 (CDT)
> Bob Friesenhahn <bfriesen at simple.dallas.tx.us> 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
>
>
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--
Rob Lingelbach
rob at colorist.org  http://www.colorist.org/robhome.html






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