Digital BW, The Print

Bob,

Several of us had a long discussion on this subject on the Epson_printers 
list about 2 or 3 yrs ago with Kennedy McEwan (if you search the archives 
for him, you will find them).

Summarising these discussions:-

Question -
    Is there a magic number eg. 360 ppi for sending images to the printer?

Kennedy -
    "The Epson Stylus Photo printer range all resample the image to 720ppi 
in
the printer driver so, in principle there is a theoretical advantage to
setting the output ppi to an integer division of this - eg. 360ppi.
However, unless your image contains high modulation at the limiting
resolution (which it certainly won't if you are scanning film at
4000ppi) then it doesn't really matter - there just aren't enough
harmonics present in the image to produce irrational resampling
artifacts."


Question -
    If the printer driver is going to resample to 720 ppi (desktop printers) 
and PS does a better job of resampling than the Epson driver, then why don't 
you recommend that we all resample our images in PS to 720 ppi before 
sending them to the printer?

Kennedy -
    "Several reasons, some of which are just as relevant as always, but
others become less relevant as the technology moves on.  In that latter
category are definitely issues about file size and processing speed.  A
couple of years ago with less than 100MB being a lot of memory and
processor speeds of the time, resampling to 720ppi would have been an
unnecessary burden - if at all practical for many systems to cope with.
With todays speeds and memory allocations, that is not as much of an
issue, but a lot of machines will still struggle.
    In the former category are consequences of the stochastic dither
algorithm used by Epson, which can produce unwanted fine detail
enhancement if sent data at full resolution.  This can often result in
unexpected granularity in the image which is similar but not the same as
grain aliasing.  Another aspect is the printer settings itself which may
result in a slight scaling if set incorrectly, resulting in very large
alias patterns which are well within visible resolution limits with
720ppi source material."


Question -
    OK then, what ppi should we send to the printer?

Kennedy -
    "as long as the resolution is between 240 and 480ppi,
then I just use what I end up with.  If it is less than 240ppi or more
than 480ppi then I use bicubic resampling to get 360ppi.  If it is also
greater than 720ppi, then I select 720ppi as the target, but this only
occurs for small prints with the source equipment I use."



Nothing in life seems simple, does it?

Bob Frost.


----- Original Message ----- 
From: "B. Campbell" <bellis60@...>

So it really doesn't matter what I send to the printer, the printer
will always upsample or downsample to 720 dpi. I never knew that, I always
thought the printer printed the same dpi as the ppi I sent to it, e.g. if I
sent it 600 ppi it would print 600 dpi at whatever printer resolution I
chose. I assume though that it's still better to send more ppi to it so that
the amount of upsampling is minimized or is that not correct either?