Re: [Gimp-print-devel] the speed is the same using bidirectional and unidirectional

[Robert L K. <rl...@al...>]

   From: Zhang Weiwu <zha...@re...>
   Date: Sun, 25 Jun 2006 10:46:52 +0800

   > Hello. Using gutenprint RC3 on Gentoo Linux over UltraSparc 5, Epson
   > Stylus Photo 830U printer connected to NEC's USB controller card, in USB
   > 1.1 mode.
   > 
   > The print prints in almost the same speed in unidrectional and
   > bidirectional mode, and the print result looks identical.
   > 
   > == Unidirectional Mode ==
   > 
   >         Speed: 3.028 minutes per A4 page (color brochure), tested by
   >         continuesly print 72 pages. Average CPU usage is 60%.
   >         
   >         The printer keep busy working.
   > 
   > == Bidirectional Mode ==
   > 
   >         Speed: 3.1 minutes per A4 page (color brochure), tested by
   >         continuesly print 102 pages. Average CPU usage is 80%.
   >         
   >         The printer DO NOT KEEP BUSY WORKING. Often the print head goes
   >         to one side, wait 2 to 3 seconds, then goes back. It seems the
   >         more complex the image is, the print head waits longer before
   >         goes back, on single color background part the print head goes
   >         immediately back.
   >         
   > It shows that Bidirectional is a little bit slower and consume more CPU
   > resource, I don't understand why. 
   > 
   > Further I don't know what the print head is waiting for when the image
   > is complex. Is it waiting for CPU? perhaps, CPU usage hit 100% percent
   > once several seconds, but average is just 80%. Is it waiting for data to
   > send to USB? I think USB 1.1 at full speed can transfer 15Mbps, it's
   > maybe not so easy to hit the peak, unless if USB 1.1 is running in
   > 1.2Mbps mode, which I got no way to tell.

I think you're CPU-limited here, not USB limited (even in 1.1 mode) in
bidirectional mode.  Your CPU usage is high.  In unidirectional mode,
the printer takes longer because the head has to return to the left
for each pass, and that's enough extra time so that the CPU can keep
up.  I don't think that that printer can come close to keeping up with
USB 1.1 rates -- the R300, which is a much faster printer, can't.

   > How can I make it prints faster with same or only a bit lower quality?
   > Any suggestions?

My suggestion would be to specify the Dither Algorithm as Ordered; by
default it's probably using EvenTone, which is quite slow.

   > Why we need such lot CPU resource to do a printing? The processor
   > is 64-bit 300MHz sparc, I thought this is pretty fast for an
   > inkjet print server. Besides it is rastertogutenpr that is eating
   > up the CPU resource, there are only one page being printed many a
   > copies, thus rasterlizing it is done once only, long before, so
   > why there are so much to do for rastertogutenpr? (sorry,
   > completely newbie question).

Because the way CUPS works it has rastertogutenprint regenerate the
output each time rather than saving it away.

-- 
Robert Krawitz                                     <rl...@al...>

Tall Clubs International  --  http://www.tall.org/ or 1-888-IM-TALL-2
Member of the League for Programming Freedom -- mail lp...@uu...
Project lead for Gutenprint   --    http://gimp-print.sourceforge.net

"Linux doesn't dictate how I work, I dictate how Linux works."
--Eric Crampton