Just to clarify. DPI is far from irrelevant to people who print. which is
A
LOT OF PEOPLE. (or if you are using a RIP) LPI an DPI. How many DPI
linearly Make up your LPI.
My uncle bought a printing company and was very pleased when I was able to
hand over piles of halftone screens to him from the advanced dip science
course I taught - admittedly the science course specialty was photography,
mostly optical physics and chemistry, but I also taught some of the Adv Dip
Art students studying graphic design too.. so I was able to salvage so much
when all the print presses and affiliated gear was thrown out.
Of course this was more a decade back. I still have a collection of screens
but no one wants them any more. I think it took him 6 months before he
too ditched the screens, process cameras and went fully 'digital' -
outputting from file to plates which would then etch and be ready for
printing without ever seeing a half tone screen or him knowing a jot about
dpi. That was the advantage of a 4 color RIP in the print game - just drop
the image in the software, load the photosensitive plates, etch them and
drop them on the drum - no theory needed any more. He was a mathematician
so he appreciated the fun side, but work is work and if there's an easy way
to do it..
Of course photo printers are a different game. There your 4800 or so dots
per inch are still handled by a RIP, and similarly now, it's something the
user need know nearly nothing about - they just tell the printer for a
draft on plain paper and they get the heavy 360 dots per inch, or they ask
for a photo quality on fine paper and get a fine spray of the whole 4800
dots, precisely picked and patterned to use all 4800 dots of the 6 or 8 inks
to make the colours needed.
Also the frequency thing is sort of
important as well if you are printing to a 4 color press that is using
halftones. In a RIP all those things can be adjusted to create better
image quality even on a desktop inkjet.
Good explanation here (of 4 color)
http://the-print-guide.blogspot.com/2009/04/rosettes-everything-you-didnt-realize.html
good quote:
"Photoshop has a very poor halftone screening algorithm so you cannot get
either clear or dot centered rosettes using it." RIPS are often better at
output tasks. I wish I'd had access to better rips years back when I was
playing with the tektronix phasers. That was a waste of good money
experimenting with horrendously expensive early colour print tech! Good
source of parts for other projects though once they were pulled apart ;)
In a digital single chip Camera every pixel represents 3 DOTs.
(or more commonly 3 dots represent 3 interpolated pixels) I was reminded of
this on the list many many years back. It was explained that a sensor of
300 x 400 pixels for example uses groups of 3 pixels to determine colour,
then each of those 3 pixels was allocated a colour and luminance to produce
the 300 x 400 total pixel image.
A pixel
represent how ever many dots the software or hardware chooses to use to
make up that pixel.
I usually see a PixEl defined as the smallest element of an image, but yes,
the dots in a print are made of ink dots - And while technically each dot by
definition could therefore technically be called a pixel, I don't think I've
ever heard dots described that way.
Second Order Stochastic CMKY. Random dots of random size (not really
random as its controlled by the SCREEN frequency.) You can see there are
grouped into little circles. Those little blobby circles are Printer
dots.
http://static5.depositphotos.com/1001655/463/v/950/depositphotos_4634956-Cmyk-dot-pattern-vector.jpg
Interesting image - it looks a lot more like a halftone screen generated dot
pattern than an inkjet printer pattern - there's many more patterns and the
information on the methods by which they were created here:
http://www.metropostcard.com/techniques11.html (I LOVED this quote! "
inkjet printing is nothing new; its principals were patented by the
physicist Sir William Thomson in 1867 but a workable model was not close at
hand") A good collection of images under high magnification and certainly
interesting from an academic point of view.
k
