Digital BW, The Print

Bob, I think you may be mixing up pixels-per-inch (PPI) and
dots-per-inch (DPI). PPI is about your image in Photoshop; DPI is about
the dot pattern (dither) the printer driver uses to paint your image on
paper.

In your example, your image has 4800 x 6000 total pixels. When you
change the image size without resampling, Photoshop changes the PPI
accordingly, from 1200 to 600, since the total pixels don't change.

When you send the image to the printer, the driver uses your image size
& PPI to print the image the right size. And it uses the driver settings
to determine the DPI -- lots of tiny dots for highest quality but slower
printing, or fewer, larger dots for faster printing with (possibly) less
quality. If you send the printer, say, 240 PPI and print at 1440 DPI,
each pixel you send the printer turns into many dots.

Hope this helps.

Richard Wolfson
Fine Art Photographer
Digital Imaging Consultant
Harvard Massachusetts USA
rw at RichardWolfson.com

> -----Original Message-----
> From: B. Campbell [mailto:bellis60@...] 
> Sent: Friday, November 12, 2004 10:00 AM
> To: DigitalBlackandWhiteThePrint@yahoogroups.com
> Subject: Re: [Digital BW] dpi and stuff
> 
> 
> > Make sure you do not muddle ppi and dpi. Your images are in ppi
> (pixels per
> > inch) and are resampled to 360 or 720 pixels per inch in the driver.
> The
> > driver then turns each pixel in your image into several dots of ink,
> and the
> > size and spacing of those dots of ink is varied when you select 360,
> 720,
> > 1440, 2880, or 5760 dpi printer resolution in the driver.
> 
> 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?).
> 
> ----- Original Message -----
> From: "Bob Michaels" <bob@...>
> To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
> Sent: Thursday, November 11, 2004 10:45 PM
> Subject: Re: [Digital BW] dpi and stuff
> 
> (snip)
> 
> Bob Michaels
> 
> --- In DigitalBlackandWhiteThePrint@...m, "Bob Frost"
> <bob@f...> wrote:
> > Dean,
> >
> > Epson desktop printers (up to and including the 1280/90 and
> 2100/2200 all
> > resample your images in the driver to 720ppi. Epson WideFormat 
> > printers (3000 and above) all resample to 360dpi. This info is from 
> > Epson
> themselves.
> >
> > Make sure you do not muddle ppi and dpi. Your images are in ppi
> (pixels per
> > inch) and are resampled to 360 or 720 pixels per inch in the driver.
> The
> > driver then turns each pixel in your image into several dots of ink,
> and the
> > size and spacing of those dots of ink is varied when you select 360,
> 720,
> > 1440, 2880, or 5760 dpi printer resolution in the driver. In some
> drivers
> > now they don't list these resolutions; they just give you 
> the choice 
> > of photo quality, best photo, super photo or some such names to hide
> the actual
> > resolutions (probably because many people were confusing 
> the printer 
> > resolutions with the image resolution).
> >
> (big snip)
> 
> 
> 
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