Hi!
Most inkjet printers, including cheapo entry-level ones, advertise very
high resolutions like, 2880 or 5600 dpi...
In fact, these figures give the positional accuracy of individual ink
dots. At this native resolution, there are a very limited number of
colours: each position on the paper either receives, or not, a drop of
every ink color. With a 4-inks printer, each point can get:
- nothing (white)
- black dot
- cyan dot
- magenta dot
- yellow dot
- cyan + magenta (blue)
- cyan + yellow (green)
- magenta + yellow (red)
... for a total of 8 colors (black can't be mixed with other colors, and
mixing C+M+Y doesn't make much sense: would be a "dirty black").
These are theoretical figures, and do not consider blending and such.
For printers with more ink colors, do your own math.
This isn't much, and to get continuous tones (256*256*256=16M colors),
the printer must use dithering, by arranging these 8 colors in a
pattern, that look like a continuous tone pixel to the naked eye.
Wikipedia will explain this much better than I could ever do:
http://en.wikipedia.org/wiki/Dither#Digital_photography_and_image_processing
or
http://tinyurl.com/mvwuf
In short, the greater the difference between the image resolution and
the medium (printer) resolution, the better color approximation one can
get. With 5000+ dpi, and a 300dpi image, each pixel is 16 dots wide on
the paper, which leaves plenty of room to represent accurate color.
With ordered dithering technique, this ratio between the print
resolution and the image resolution is fixed: each image pixel will be
exactly and always 16x16 dot positions for instance, and it is important
to stick to fixed resolutions.
With error diffusion techniques, there is no such restriction, and a
great deal of adptation. Sharp edges can even use higher resolution than
continuous areas, which need less definition, but greater color
accuracy. In theory, the precision of continuous tones is not limited,
while the full native resolution is available for a black & white edge.
Nowadays, error diffusion is commonly used for photo printing, and
ordered dither is only used for computer graphics, charts, etc...
For a photographer, the bottom line is:
- For inkjet printing, don't care about your image's resolution.
234.56dpi is fine, anyway the printer is 5000+ dpi and does error diffusion.
- For continuous tone printers, ask the native resolution and stick
to it. These printers (DLP, laser...) can print directly in continuous
tone, but have a "low" native resolution (300 or 400dpi). If you do
234.56dpi, it would have to be resized to 300 or 400dpi first, and you
don't control the quality of this resize.
Regards
Patrice
Shel Belinkoff a écrit :
What does all that mean?
5000+ dpi ... seems like a lot, perhaps excessive. Can you explain?
What's an "error diffusion pattern?"
What's "DLP technology?"
Shel
As it is inkjet, with probably 5000+ dpi dot pitch and error diffusion
patterns, there is no real need to stick to the machine's hardware
resolution, like with digital minilabs based on DLP technology. I don't
seriously intend to print anything this size anyway!
