Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, Tony 
Terlecki <ajt@m...> wrote:

> 
> I know that. I think, as usual, I am not making myself clear. Let 
my try
> again. What I am saying is that prior to the driver doing its own
> conversion from pixels to dots it may first do its own conversion 
to
> resample the image to a fixed pixel resolution. 
> 
> Let's say the code routine in the driver which perfroms the 
pixels->dots
> conversion has been written so that it can only accept an input 
resolution
> of 360ppi. There will be a routine in the driver which would then 
first 
> check to see whether the image resolution passed to it by the 
imaging
> application/print spooler is at the correct resolution to be 
passed to the
> pixels->dots function, and if not, it will do this resampling. Note 
there
> are two separate things happening here in the print driver:
> 
> 1. Resampling to a fixed PPI.
> 2. Conversion from PPI to whatever dpi/dither algorithm is 
used by the
> printer and generation of the printer commands for the actual 
print.
> 
> It is this first step which I am contending could be sidestepped 
simply by
> sending the correct PPI image to the printer.

Tony,

You are correct here at least for some drivers.  In the print
facility for OS X, Linux, and other Unix systems the file
is resampled in PIXELS to the resolution that you pick for
DOTSpi.  I.e. the first step in getting a 1440x720 DPI print
is to get a 1440x720 PPI raster that is then processed into
ink dots.

I've read documents from Epson (but I'm not sure where)
that as least implied that the desktop drivers typically 
resample to 720 PPI before dithering.

Now whether or not to resample a 537.2ppi image to 720ppi
in Photoshop rather than the driver is may be theoretically
beneficial but pragmatically unlikely to make any difference on 
the print.  But I certainly wouldn't resample down to 360ppi,
hence I pretty much agree with the idea of not resampling
any extra.

Roy

> 
> My question really was "where does the PPI resampling of an 
image happen, if
> indeed it happens at all"? I'm not talking about the conversion 
of the pixel
> data into the cmyk dots that go down as a dither pattern, just 
the pixel
> resampling of the image. I am, above all asking whether it is 
an atomic
> transformation which happens at exactly the same time that 
the pixel-dot 
> conversion is done, whether is it a step which occurs before 
the pixel to
> dot transformation although still within the driver, or whether 
there is
> actually no resampling of the image data by the print driver 
prior to the
> conversion to actual printer dots.
> 
...
> 
> Tony