Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "hlockwood"
<hflockwood@...> wrote:
>
> It appears that my membership in this group has been reestablished,
thanks to the moderator, Antonis.  I greatly appreciate his effort.
>
> Yahoo certainly needs to get its house in order to avoid foul-ups like
this in the future.
>
> So, let's see if this message actually gets posted.  If successful,
I'll repost the message to Pierre on printing resolution.  With that,
perhaps we can get some clarity on this issue through the collective
expertise of this group.
>
> Harry
>

O.K., here is the original message that got lost in Yahoo land:



--- In DigitalBlackandWhiteThePrint@yahoogroups.com, Globe Trotteur
<unglobetrotteur@...> wrote:

>

>

> I assume not everybody is using Epson printers in this forum.360 ppi
is the preferred resolution for Epson. What about HP or Canon? is it 300
ppi? Thanks for the feedback.Pierre

>




Well, Pierre, I believe you're opening a can of worms.  But let's go
fishing!




What I "know" is what I've gleaned from multiple sources, some reliable,
others less so.  And all my remarks are based upon Epson printers but
can easily be transcribed to other brands.




Firstly, the native resolution of  (all?) Epson printers is 1440 dpi,
not 360 dpi.  The choice of printing resolution then depends upon the
final print size and the question of resampling, up or down, and as
we'll see, viewing distance.




It is recommended, for instance, that the chosen resolution be an
integer divisor of the native resolution that results in a rational
fraction.  That is: 1440/2 (720); 1440/3 (480); 1440/4 (360); 1440/5
(288); 1440/6 (240); 1440/8 (180), etc.  Note that 1440/7 = 205.57, and
is, therefore, not recommended.  The rationale seems to be that these
choices will, as a first step, avoid resampling by an unknown algorithm
in the Epson driver.




Furthermore, the conventional wisdom is that one should choose one of
the above resolutions that avoids up-sampling in favor of down-sampling
for the given print size.




For instance, suppose one has a scan of a 35mm negative at 4000 ppi (not
dpi!) for a pixel count of ~5670 in the long dimension, and the
intention is to make an 18"x12" print.  Then 5670/18 = 315 dpi
(approximately).  So, printing at a resolution of 360 dpi would require
up-sampling, and the conventional wisdom cited above would suggest,
instead, printing at 288 dpi.




I have personally done this test, and I was able to see small, but real,
differences in quality between 360 dpi and 288 dpi for such a print. 
However this difference was visible when I viewed the print a from a
distance of a few inches.  From a normal viewing distance I would not
have been able to see what I saw up close.  So, viewing distance is a
vital ingredient in the mix as well.




The print driver subtracts pixels in down-sampling and adds pixels in
up-sampling.  How the Epson algorithm accomplishes this is not in the
public domain.  But I'm aware of third-party software that purports to
use algorithms that optimizes the processes.  That would seem to support
the contention that re-sampling is an issue not to be ignored.




There, that is the extent of my knowledge and practice.  I'm hoping that
the true experts on this forum will set the record straight.




Harry



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