QTR-Quadtone RIP

Hi Oliver,

The gimp-print version I started with is way back -- 4.3.5.   I haven't
changed much of the dither code but have tweaked many of the tables
to get much more accurate parameters such as ink drop sizes.

The whole dithering issue is interesting and there's a lot of 
non-intuitive
aspects of the problems.  The eye catches amazingly subtle patterns.
Speed of algorithms is very important. The shear amount of data that has
to get processed is quite astounding:  consider an R800 printing an 8x10
at 2880x1440 dpi.    That's 8x10 x 2880x1440 locations on the page.
That's 330 million locations, x 8 inks, 16bit = 2byte internals.
Total of 5 gigabytes processed for an 8x10!
What about the guy doing a banner on his 9600 -- 40 in x 25 feet?

On the other hand the idea of having multiple lighter grays is to make 
the
dither less and less visible.  As long as there isn't an obvious pattern
that sticks out like a sore thumb its usually OK.

One difficulty with some of the fancier algorithms is that they are ink 
dependent.
With different inks they may show no benefit or may actually be worse.

Roy

On Tuesday, September 27, 2005, at 07:55  PM, Olivier wrote:

> Thanks Roy,
>
> Since it's a Gimp based processing I'll try to get more info on the
> Gimps forum.
>
> Could you possibly let me know the Gimp version used in QTR : there's
> been some questionning about it inb the past and I saw the latest QTR
> beta uses files dates July 5th 05 : have you updated the print engine
> or anything recently ?
>
> Thanks again
>
> Olivier
>
> --- In QuadtoneRIP@yahoogroups.com, "Roy Harrington" <roy@h...> wrote:
>>
>> There's really only two dithering methods that I think are worth
> looking at.
>> They are Ordered and Adaptive Hybrid.  From looking at the code
> both Floyd
>> and Eventone just do Adaptive Hydrid.  Fast and Very Fast aren't
> that good as
>> far as I can tell.
>>
>> The results from Ordered and Adaptive are pretty close -- they are
> different but
>> overall give similar results.  On any given image there may be
> visible differences
>> but I had a hard time conclusively saying one was clearly and
> always better than the other.
>> Early on I remember seeing an occasional yet rare artifact in the
> Adaptive dither
>> on specific test prints - not real photos.  That combined with the
> noticeably faster
>> algorithm for Ordered, I always use Ordered.
>>
>> Ordered dither is the only one that I can say I mostly understand.
> There seem to
>> be some docs that imply that it doesn't do well with variable dot
> sizes.  I don't in
>> general find that to be true but I have been experimenting with the
> handling of
>> variable dot sizes.
>>
>> Roy
>>
>>
>> --- In QuadtoneRIP@yahoogroups.com, "Olivier" <odesmais@y...> wrote:
>>> Based on this 3 links :
>>>
>>> http://gimp-print.sourceforge.net/developer-html/gimpprint_26.html
>>> http://man.digipedia.pl/man/man7/gimpprint-dithers.7.html
>>> http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00BR5g
>>>
>>> it's very hard to find out the effects of each dithering methods
>>> (except "fast" and "very fast" are not adapted to fine BW prints).
>>>
>>> The thread from photonet states that only ordered,fast and
> Adaptive
>>> Hybrid are implemented in QTR ?
>>>
>>> The one from sourceforge seems to recommend Adaptive Hybrid since
>>> ordered is only preferable for 4colors none variable dot sized
>>> printers, A/H would use error diffusion in dark & halftones and
> ordered
>>> in light tones.
>>>
>>>
>>> None of these papers is too explicite. Any additonal comments
> from
>>> better experimented people than me...
>>>
>>> Olivier
>>>
>>>
>>> --- In QuadtoneRIP@yahoogroups.com, "Olivier" <odesmais@y...>
> wrote:
>>>> John, thanks for the below. In fact I'm looking for an
> explanation of
>>>> how the different dithering methods calculate the print and the
>>>> difference between each.
>>>>
>>>> Olivier
>>>>
>>>> --- In QuadtoneRIP@yahoogroups.com, "John Moody"
> <moodymz3@y...>
>>> wrote:
>>>>> The reply has not changed, but I have been using eventone for
> matte
>>>> paper at
>>>>> 1440 super, and ordered for luster at 2880 dpi with the R200
>>> printer.
>>>>>
>>>>> Best regards,
>>>>> John Moody
>>>>>
>
>
>
>
>
>
> Yahoo! Groups Links
>
>
>
>
>
>
-
Roy Harrington
roy@...
Black & White Photo Gallery
http://www.harrington.com