Re: filmscanners: File sizes, file formats, etc. for printing 8.5 x 11and 13 x 17...

[Arthur Entlich <artistic@ampsc.com>]

There is a big difference between halftoning and dithering.  Most of the 
printers we use, inkjet, home laser printers, etc, use dithering.

Halftoning involves having each ink color screened into dots and then 
each of these dots is further matrixed to create different color 
density.  So the cyan ink, as an example, is printed in a manner such 
that each "dot" is further matrixed into many smaller dots of varying 
size.  The matrix is rigid, in that the position of each dot is 
equidistant from any other.  The matrix can be as many as 256 smaller 
dots (16 x 16) per larger dot, in very high end printing, and that 
bigger dot is still pretty small; how small each of these matrixed dots 
is determines the lpi (lines per inch).  This is done for each of the 
four ink colors.  Each color os then printed on a different angle 
(creating a rosette) to allow for the paper to receive the ink and yet 
care is taken to avoid harmonics that create moire patterns.

This can be accomplished in the printing realm because viscose inks are 
applied to an etched plate, which allows for very fine detail.  That 
type of control is not possible with dye inks used from a nozzle, like 
an inkjet.  Further, it would take forever to print, even if the 
resolution was possible.

Although "AM screen" type distribution patterns can be used for inkjet 
printing or laser printers, it usually looks pretty bad.  1200 dpi 
monochrome lasers handles screens fairly well.  Usually, more random 
dithering patterns (FM stochastic dots) look better as the eye can see 
the coarser patterns too easily and they are too uniform.

Dithering involves placing solid colored dots in patterns near each 
other to trick the eye into seeing a secondary color.  Inkjet printers, 
typically use dithering patterns.  No inkjet printer can produce true 
halftone, yet.

Art


Austin Franklin wrote:

>> Impact printers, laser printers, ink jet printers ... any printer
>> which needs to dither some sort of CYMk pattern for creating
>> "apparent" colors have a DPI resolution specification which should be
>> considered separate from the RGB resolution you ask them to print
>> (PPI).
> 
> 
> I understand your distinction, thanks.  It's probably a very important
> distinction to understand, I guess I have always taken for granted.
> 
> Now, another question...why do you call it 'dither' instead of halftone?
> Dither is different than halftone.  Here are the definitions I have for each
> of those:
> 
> "Dithering is a process in which an application chooses two or more colors
> from a palette, and then applies them to adjacent pixels to approximate
> colors outside of the palette."
> 
> "Halftoning is the process of breaking down a continuous tone image into
> solid spots of differing sizes to create the illusion of transitioning grays
> or colors in a printed image."
> 
> 
> 
>> For example, many believe
>> 240LPI is optimum for 720DPI Epson printers, and you'd teherefore ask
>> the printer to print 240PPI.
> 
> 
> Possibly 'mis' believe, but that's another topic ;-)