Xref: utzoo comp.graphics:7681 comp.sys.ibm.pc:35553
Path: utzoo!attcan!uunet!jarthur!jleonard
From: jleonard@jarthur.Claremont.EDU (Jon H. Leonard)
Newsgroups: comp.graphics,comp.sys.ibm.pc
Subject: Re: Print a 75 ppi image on a 300 ppi laserprinter
Keywords: Alogarithsm to show the depth
Message-ID: <2220@jarthur.Claremont.EDU>
Date: 1 Oct 89 00:09:14 GMT
References: <814@dukempd.phy.duke.edu>
Reply-To: jleonard@jarthur.UUCP (Jon H. Leonard)
Followup-To: comp.graphics
Organization: Harvey Mudd College, Claremont, CA
Lines: 39

In article <814@dukempd.phy.duke.edu> fang@dukempd.phy.duke.edu (Fang Zhong) writes:
>... 75 pixel per inch and eight bits per pixel.
>	We want to print the images on a HP series II laserprinter with the
>resolution of 300 pixel per inch.  One pixel on the monitor can be represented
>by 4x4 pixels on the laserprinter.  Since there is only one bit per pixel on
>the laserprinter, we thought that we could decorate the 4x4 pixels correspondingthe original eight bits depth.
>	Has anyone done this before?  What the alogarithsm is used?

	I've used a Laserjet II to print greyscale images by using only some of
the dots.  The limitation is that for a 4x4 blocks there are only 17 different
grey values possible, (moving dots doesn't change how dark it looks) so most
of the 8-bit information would be lost.
	What I did was to pick a method of getting a value from 0 to 16
for each of the output pixels, and then set the pixel only if the value for
the matching location in a mask grid was less than or equal to the pixel value.

The grid I used was a repetition of

	1  9  3 11
       13  5 15  7
        4 12  2 10
       16  8 14  6

This looked ok, but I found that a 8x8 grid (65 grey values) was needed for
 output to look nice.  This can be done without sacrificing the 75 dpi
initial resolution -- not having all the pixels in one block the same is ok. 

>... Is there
>a way that we can send half image to the laserprinter and have it printed,
>then send the another half afterwards?

	Beyond running the same piece of paper through twice, no.  (To do
that, just set the location of each half of the image right for each pass.
It works, but has alignment problems and is a kluge.)  It is possible to print
 a half page of 300x300 graphics on an unexpanded Laserjet II, so this or
 small images work fine.  A 1-meg memory expansion is a better solution.

	Jon Leonard
        jleonard@jarthur.claremont.edu