info-mac@uw-beaver (info-mac) (07/16/84)
From: Thomas.Newton@cmu-cs-spice.arpa I appear to be wrong about MacPaint skipping lines on the printout. I tried printing some horizontal lines arranged in a staircase fashion, and none of them were missing on the printout. The Imagewriter manual DOES say, however that vertical resolution is 72dpi and that horizontal resolution in graphics mode is either 144dpi or 160dpi. The Macintosh screen is roughly 80dpi. So how does the Mac adjust for the fact that the printer does not have the vertical resolution of the screen? When I held a printed document to the screen, I noticed that the printed version was slightly larger. Apparently MacPaint is printing documents at 72dpi, which makes actual printouts about 10% larger than their size on the screen. Given the alternatives, this seems like a very reasonable choice. Of course, if the Imagewriter could print 80dpi in both directions (so that it could print things exactly as they appear on the screen) and had tractor feed (to minimize paper shifting), none of this would ever have come up.
info-mac@uw-beaver (info-mac) (07/18/84)
From: singer@harvard.ARPA (Andrew Singer)
I've seen a bit of misinformation repeated several times now on this bboard.
I'm quite surprised that no one has yet picked up on it. Permit me to
rectify the problem once and for all by quoting directly from the QuickDraw
Programmer's Guide (Inside Macintosh version) section on "The Bit Image":
"The Macintosh screen itself is one large visible bit image. The upper
21,888 bytes of memory are displayed as a matrix of 175,104 pixels on the
screen... The screen is 342 pixels tall and 512 pixels wide, and the row
width of its bit image is 64 bytes. Each pixel on the screen is square;
there are 72 pixels per inch in each direction."
In light of this, it should not be too difficult to see how the Imagewriter
can print a screen image with only 72 dpi vertical resolution...
I have duplicated the test of holding the printout up to the screen and found
that, indeed, the printed image is slightly larger than the screen image. This
I cannot explain, unless it is due to the fact that an "inch" is slightly
different on each (the printed copy was much closer to an actual inch).
Even so, it does not really matter unless the respective "inches" are
wildly different. What does matter is that the "aspect ratios" of both the
screen and the printer are well matched; thus printed copy of a screen image
will always be faithful, if not exactly the same. Anyone who has used a Lisa
can tell you that the Lisa's 60 by 90 pixel per inch screen causes no end of
problems in trying produce faithful printed copy.
Although the problems with the pin-feed of the Imagewriter remain, I have
seen Macintosh screen images dumped via a 720 dpi laser typesetter. They are
quite spectacular. When the laser printers arrive, I expect everyone will be
much happier...
Jon F. Hueras
<singer@harvard>