[Desktop_printing] Current PCL laser drivers are SLOOOOWW!

Hin-Tak Leung hintak_leung at yahoo.co.uk
Sat Feb 18 18:25:48 PST 2006

Michael Sweet wrote:
> Till Kamppeter wrote:
>> Michael Sweet wrote:
>>> PCL 5 and HP-GL/2 generally don't do 1200 DPI; there are exceptions
>>> on high-end DesignJet plotters, but none of the PCL 6 capable printers
>>> in my lab will do 1200 DPI in PCL 5 or HP-GL/2 mode.
>> I think we definitely need also such a driver for PCL 6/XL devices. Is
>> the currently known (by free software developers) amount of PCL 6/XL
>> enough for such a driver?
> It should be - the current Ghostscript pxlmono/pxlcolor drivers seem
> to work fine with our PCL 6 devices, and I have some pending changes
> that will add support for PJL-based finishing features...

Osamu MIHARA wrote:
 > Hi,
 > As to the PCL vector driver information, please refer Toratani-san's
 > post.  The PCL vector driver uses PCL5/HPGL vector feature.  If my
 > memory is correct, PCL5 does not contains vector feature, but HPGL does.
> We, OpenPrinting Japan team, had been trying to develop a PCL6 (or PCL/XL)
> driver, but the specification for PCL6 is not OPEN for public (although it may
> be well known among the HP's competitors;) So, we did use PCL5/HPGL instead.

As noted, the PCL6/PCL-XL specs is fairly well-known to quite a number of us...
(and yes, I "believe" it has "confidential" or some such words plastered all
over the place :-), a somewhat strange practice given that it is quite readily 
downloadable from authentic HP web sites...).

In fact I have discussed this with Till and the HPIJS people about speed of B/W
printing and how hpijs's PCL6/XL code works; and I have looked at pxlmono
since, and also cups' rastertopclx (I haven't really looked at
PCL5 implementations, but ghostscript ljet4 driver is miles faster
than pxlmono/pxlcolor, at the "same default 600 dpi") because all of them
emit 24-bit color raster data to the printer, regardless of whether the
printer uses the color info. Here is how I understand each of them works:

pxlmono: receives 24-bit data from upstream, send "@PJL SET 
RENDERMODE=GRAYSCALE" (instead of "COLOR") in the header and
send full 24-bit color data to the printer. (i.e. a gray spool job
is 4-byte larger than a color spool job)

hpijs: receives 24-bit data from upstream, flatten the color - i.e.
set each of red,green,blue to luminance of red+green+blue, output
24-bit data where (r,g,b) is replaced by (x,x,x),
x=  0.299 r + 0.587 g + 0.114 b . (.e. a gray spool job is same
size as color spool job).

cups's rastertopclx: Actually I am not exactly sure how it works (or
whether it does pcl-5/HP-GL only), but it also have contructions like
and it has some rather sophisticated conversion logistics.
Perhaps Mike can explain how it deals with color data coming in destined
for a B/W-only printer?

(ghostscript and HPIJS people please correct me if I am wrong above)


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