[cups.general] Should the CUPS Raster output device ofGhostscript output compressed or uncompressed Raster data?

[Michael Sweet]

On Jul 13, 2010, at 3:57 AM, Johannes Meixner wrote:
> ...
> I do not understand how currently CUPS raster data could
> be used as a input format for printers at all?

There are some printers that actually support CUPS raster as a native format.

> ...
> In particular - as far as I understand it - the current CUPS 1.4.4
> implementation of the CUPS raster data compression in CUPS'
> filter/raster.c source file looks like a CUPS-specific implementation
> of a compression algorithm which might change at any time in any way.

While this is true, we generally try to *not* make changes to CUPS raster if we can avoid it. In particular, it took 7 years (from 1999 with the first CUPS raster format to 2006 when we released CUPS 1.2.0 with the version 2 (compressed) and 3 (uncompressed) variants) for us to decide to make a change to the format, and then only because certain drivers needed more room for options in the page header.  We spent years collecting and defining what that change would be, and then made sure we could still read and write the original format and hide the new format from filters that didn't need the extra page header options.

Compression was an afterthought, mainly to reduce the amount of bytes written for 16 bit per color data, however we quickly discovered that the overhead of compression was more than the overhead of writing all those bytes.  It is highly unlikely that we will make changes to the current compression algorithm given that it has no advantage on-system and off-system we have several other compression options (gzip/flate and compress/LZW) available via IPP to improve compression (and those actually work very well combined with the packbits compression in version 2 CUPS raster to offer excellent compression performance with lower CPU usage than flate/LZW alone...)

> ...
> For future I like the idea very much that printers should accept
> a particular standardized CUPS raster format as input format.
> But I think this needs some discussion - in particular with all
> kind of printer manufacturers - not only for printers for rough
> industrial use but also e.g. for those "weak and cheap" printers
> for home use where each cent of the hardware costs matters.


That's one of the things we are looking at in the Printer Working Group with the IPP Everywhere project; see:

    http://pwg-wiki.wikispaces.com/IPP+Everywhere

________________________________________________________________________
Michael Sweet, Senior Printing System Engineer, PWG Chair




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