Re: dots per inch?

Scott W added these comments in the current discussion du jour
....

eugene wrote:
Someone has asked me to give them an image with 350 dots per
inch. Is this the same as 350 pixels per inch?


There will be no doubt another long debate about ppi vs. dpi,
but yes if they asked for 350 dots per inch it is a very good
bet that what they really meant was 350 pixels per inch.

re: another long debate. I think you may be right here, Scott! As
best I can tell, the term DPI originated in the printing industry
for the earliest of what we now know as half-tone printing, which
is the laying down of a pattern of "dots" in a geometrically
regular pattern at an angle, often 45 degrees. In the days of B &
W newspapers, the number and size of the "dots" laid down roughly
to approximate the shades of gray in a continuous tone photo of
the day allowed the black dots and white news print to fool the
human eye into thinking they were looking at a real photo.

Later, the same idea was applied to color photos.

Much, much later, when computer scanners were invented, the term
DPI now had real meaning, in that it specified how many "dots"
the user wanted the scanner to "sample" or scan per linear inch
across the paper and down its length. Each "dot" resulted in a
pixel in the final image. AFAIK, that definition of "DPI" is
still valid.

I won't go into the debate about DPI for ink jet printers except
to say that the number of "dots" laid down by the printer in
order to "dither" to get the desired colors and density isn't at
all the same sort of definition I used above. Yes, of course the
printer is actually producing N DPI but it seems difficult for
them that aren't mathematicians to understand what is really
happening.

For us normal folk, who just want to get "good" prints from a
given pixel resolution raster graphics image, I agree with you
and most others in that "DPI" really means "PPI". I do not get
any of my images printed by pro shops nor do I dabble in
"printing" my images in publications that use today's version of
half-tone printing, but I suppose there are places that are set
up to calculate the finished print size using "DPI". One can
obviously do the exact same thing using "PPI" but perhaps older
print machines and/or older software may want DPI.

And with that, let the debate begin!

--
HP, aka Jerry
.

Relevant Pages

  • Re: dumb question
    ... DPI is an incorrect unit designation; DPI is most commonly used for scanning where the hardware scans X dots per linear inch of material, where each dot turns into a pixel. ... converted to a spot on the paper, hence the proper units are PPI or Pixels Per Inch. ... Good printers print at so many pixels per inch (PPI), the 'native' PPI for the printer; Canon uses 600PPI, and Epson uses 720 PPI. ...
    (rec.photo.digital.slr-systems)
  • Re: dumb question
    ... DPI is an incorrect unit designation; DPI is most commonly used for scanning where the hardware scans X dots per linear inch of material, where each dot turns into a pixel. ... In digital printing or processing, everything is already in pixels and is re- ... converted to a spot on the paper, hence the proper units are PPI or Pixels Per Inch. ...
    (rec.photo.digital.slr-systems)
  • Re: thematic collecting - scanning images of stamps
    ... The encoded result of the scan will be converted on a computer screen to pixels horizontally/vertically depending on the resolution of the screen; in a similar way the printer may use 600/300 dots/inch horizontally/vertically depending on the resolution of the printer head, ... I prefer to use to pixels when I refer to a computer or television screen; and to dots when talking about scanners of printers. ... ppi is the term. ... How is it my Epson shows "dpi" and Wiki siggests dpi is the language ...
    (rec.collecting.stamps.discuss)
  • Re: National Geographic vs. Canon print paper
    ... For 35mm, most people find that somewhere in the 2500-5000 DPI range better able to extract all the image information available, then resampling down to whatever they think is "right" for their purpose. ... Until it's printed, the TIFF file should be as large a resolution as the scanner created (eg: 4535x6803 pixels). ... Any imbedded info about "300 ppi" is just handwaving until it's printed out onto paper, ... You can use whatever name you want: how about blueberries per inch? ...
    (rec.photo.digital)
  • Re: National Geographic vs. Canon print paper
    ... For 35mm, most people find that somewhere in the 2500-5000 DPI range better able to extract all the image information available, then resampling down to whatever they think is "right" for their purpose. ... I would call PPI. ... To me, being the simple engineer that I am, when scanning, DPI is the correct term while when printing from an existing image in pixels, then PPI is the right nomenclature. ... If you refer to dots per inch, ...
    (rec.photo.digital)