FotoDave@aol.com
Sat, 31 Jul 1999 10:32:13 -0400 (EDT)
In a message dated 7/31/99 6:10:37 AM Pacific Daylight Time, nick@mcn.org
writes:
> I have determined that a Bitmap type of file will
> automatically render a stochastic image on an inkjet printer (do I
> understand this correctly?).
Hmmm.... not really. This must be because of your printer setup (or maybe
some default of your printer). A "bitmap" image consists only black and white
information and should thereticallly print as is. For example, if your
printing is printing at 600 dpi, and when you convert to "bitmap" you choose
the resolution of 600 dpi, then what you see is what you get unless, as
mentioned, the printer is set to different configuration or default.
But if your chosen output resolution is different from the printer
resolution, then the printer must interpolate, so what you see will be
slightly different from what you get.
> On the Epson 1520, at least on the PC/W98, the setup for the printer allows
> for the printer default screening method or for manual control of screens
> using LPI, diffusion, etc. Does this mean that the printer is able to make
> a halftone even from a bitmap output???????
Even if it is able to, that's not what you really want. If you want to use
screening, you should print from the original full-tone image. If you use
"bitmap," you have basically let Photoshop make the conversion from
continuous-tone to dot-only information, so you want to preserve the
conversion.
> By the way, my 1520 manual
> shows no reference to the word "Stochastic".
Good for them. And if you (or anyone) wants to stay ahead in digital
terminology, forget this term. I predict that this term will be completely
dropped in the future as "stochastic" screening can mean anything except
being stochastic! :)
In traditional screening, there is a fixed number of dots per inch. Lighter
or darker tones are rendered (or modulated) as bigger or smaller size of
these dots. In "stochastic" screening, there is a fixed dot size. Lighter or
darker tones are rendered (or modulated) as more or less number of these dots
(think of it as stippling method in pen & ink drawing: where you want it
darker, you put more dots; lighter, less dots).
The first method modulates tones by size, so it is called amplitude
modulation (or AM screening). The second method modulates tone by number of
dots (or frequency, so it's called FM screening).
Both these methods are fixed, predictable, and involve NO randomness or
probability. Stochastic means random or involving random variables or chance
or probability. I think someone called it "stochastic" screening because it
looks a little random, but it actually is not. The situation is like calling
an image with black dots and hard dots only but without any tone in between a
"halftone." [sigh] So much for terminologies....
> When printing a bitmap, when/why/how/what does one do to apply the proper
> number of colors (posterizing) to create maximum resolution on output to
the
> printer or is there a meaningful consideration to be learned here?
In printing a "bitmap," you should use the maximum printer resolution unless
your process cannot print it that fine, then you might as well use a lower
resolution. I have actually mentioned this about a year ago. You might want
to search the archive.
The whole thing might sound complicated in the beginning, but once you get
it, it is much simpler that it sounds. My recommendation is to read a lot on
Photoshop and digital imaging but not that alone. Read also photomechanical
printing (very very applicable) and of course read about the process you are
using. Otherwise the situation is like you read so much about silver printing
and expect to make a great carbon print. There are good Photoshop books
around, but the output is either imagesetter or printer whereas we are
interested in using those outputs as an intermediate outputs for alt.
process. We are on our own....
Dave S
This archive was generated by hypermail 2.0b3 on Thu Oct 28 1999 - 21:40:39