In article <pdb_NOSPAM-B26E83.11491229022004@news.povray.org> , Paul Bourke
<pdb### [at] swineduau>  wrote:

>> would it be possible to ask for a .png loseless compresion for some images
>> that really need it, instead of jpg qith quality=95?
>
> I you can show there are obvious visual artifacts then I'm prepared to
> display it on SCC3 in a better quality jpeg....lossless if necessary.

Usually there is no need to.  There is a little known fact about the IJGs
JPEG library: By default it always uses 4:2:0 YUV format.  The utilities
that come with it, just like many other programs, do not offer access to the
other widely supported (and specified in the IJGs format) compression
options, which allow each component to be samples at anything from one to
1/16 (i.e. you can have Y values per pixel but U values only for every four
by four pixels and V for every two by two pixels).  And then there is the
RGB format, which also nobody seems to be able to output to.  Yet, all
common decoders I know do support this - they always will if the use the
IJGs JPEG library, which nearly all open source tools use - and will create
still well compressed, but much higher quality JPEG images...

...so essentially one needs to find a tool that allows to make these
settings.  What says Jerome suggests that gimp may be supporting this and
would be the way to go in such a quality problem case.

    Thorsten

____________________________________________________
Thorsten Froehlich, Duisburg, Germany
e-mail: tho### [at] trfde

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