QTR-Quadtone RIP

momoinu_dc wrote:
> Paul-
> 
> I just reprinted the, following your suggestion.  The "overspray" was
> significantly reduced, but is still present.  The type, itself, was
> also a bit better defined.  However, the QTR print of the full 1080dpi
> file is still unquestionably superior.  What is it that QTR does
> differently (and apparently, better)?
> 
> Perhaps what this does show, at the very least, is that when printing
> a large file to an Epson printer, downsample to 720 dpi (or 360dpi, as
> appropriate)in Photoshop, or other program, before sending it to the
> printer.
>

A year ago I have done several tests with the Qimage 
resolution test target on my Z3100 to check what 
downsampling can do to a print. By changing the size of the 
target image in Photoshop to some sizes smaller and the last 
was a 1200 PPI target, both dimensions halved. That way no 
resampling on the file itself happens in Photoshop so you 
get higher resolution targets without changing their image. 
Printed 1:1, two targets at the same time, one rotated 90 
degrees to see whether paper transport resolution differed 
from head transport resolution. Gloss paper. Qimage was used 
to print and the downsampling to native resolution was done 
either by Qimage or the Z3100 driver with Qimage's 
extrapolation settings off. Some with anti-aliasing on in 
Qimage when Qimage did the downsampling. Some with 
anti-aliasing off. In general all the prints were different 
to one another. Shifts to higher contrast (due to aliasing), 
moir\ufffd building and with the Z3100 driver downsampling, 
disappearence of complete hatched areas where other hatched 
areas became black (aliasing again), etc. Most of that is 
solved by using anti-aliasing routines but the quality of 
the routines differ a lot per application as Bart van der 
Wolf samples already showed a long time ago. Mechanical 
resolution of head or paper transport had little influence. 
The finest line hatches in the 1200 PPI target disappeared 
with Qimage's AA routines and downsampling but the resulting 
gray was equal in tone to the gray of the hatched areas 
where the lines were sharp. No contrast shifts.
The targets are not normal photographs but lines, small text 
etc. However you will see similar things happen in 
photographs depending on the content, texture (grass, corn, 
textile, whatever), scanned grain, etc.

Too often I see statements (LL forum) that one can drop any 
file resolution above say 240 PPI on modern printer drivers 
and it will make optimal use of the data ...... It just 
isn't true. In upsampling nor in downsampling.

http://www.xs4all.nl/~bvdwolf/main/foto/down_sample/down_sample.htm
http://www.xs4all.nl/~bvdwolf/main/foto/down_sample/example1.htm

Qimage targets:

http://www.ddisoftware.com/qimage/quality/

read the article as well there.

As explained above I used the targets in a different way as 
well, sending a 600 PPI target to the printer where the 
driver requested 300 PPI as the native resolution for the 
selected quality setting, sending a 1200 PPI target to the 
printer where the driver requested 600 PPI as the native 
resolution for the selected quality setting.

On small text: if you have anti-aliased fonts for a given 
resolution you will get worse font description when the 
resolution is changed again for that bitmap with fonts. So 
do the rasterisation + anti-aliasing of the vector font at 
the native resolution of the printer with the font size it 
will get in print. Or do it at a resolution twice that of 
the native resolution for really small text (cards etc), 
even a nearest neighbour downsampling will do then. Odd 
sampling ratios make text worse.


-- 
Met vriendelijke groeten,  Ernst


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