Digital BW, The Print

B. Campbell wrote:

> Hmm. After reading Wayne Fulton's book years ago and thinking I understood
> all this I'm now muddled. Assume I scan a 4x5 negative at 100% at 1200 ppi.
> I then open the Image Size window in Photoshop and change the image size to
> 8x10 without resampling, which changes the ppi from 1200 to 600 ppi (ignore
> the fact that the image in my 4x5 negative isn't really quite 4x5). I
> thought that if I then sent the image to the printer, setting the quality in
> the printer window at 720, 1440, 2880 or whatever depending on how fine
> wanted the size and spacing of each dot to be, my 8x10 image would print at
> 600 dpi. (and the spacing and size of each of those 600 dpi would be based
> on whatever quality I set in the printer window).
> 
> But if I understand you correctly you're saying that this is incorrect and
> instead of printing at 600 dpi in the above example my 1280 printer will
> ignore some setting of mine and instead will always print at 720 ppi (or
> dpi?). At what point in the process does this occur (i.e. which of my
> settings does the printer ignore and decide for itself that 720 dpi/ppi is
> the setting at which it's going to print?).



You can't call it "ignore", the process in the driver to print at
a certain DPI requires a related PPI number image at some point.
The Epson printer drivers will internally rasterise the image to
either 360 or 720 PPI with a crude bicubic interpolation (or
worse with older drivers). After that the image is split up to
the different ink channels on the DPI print resolution set. By
feeding the driver a resolution of 360 or 720 PPI you can avoid
the extra inter/extrapolation in the driver. Qimage solves that
issue in an elegant way, it checks the desired native resolution
(API-Windows) and samples up or down with the best algorithms
available today and feeds that to the driver. If desired it also
adds print sharpening, something you will like to have in the
print but not in your file. So with Qimage you better keep the
resolution in your file that you got with scanning (or from your
digital camera) and avoid up or down sampling in the editor which
usually will do a worse job than Qimage.

There's a huge difference between DPI and PPI.
If you want to print at 600 DPI you need a Canon, HP or alike
which are based on a 150-300 ---- 1200 range of DPI resolution
numbers. The Epsons, Rolands, Mutohs have a range of 180-360 ----
1440 etc range of DPI.  Stay above 1000 DPI and it doesn't matter
what range you choose.


Ernst