crean@ny1mm.DEC (06/04/85)
I'd like to build a simple device for turning photographs into
raster-scan text files. (You know -- various characters in each
line/column to approximate various shades of gray.) The problem
is that I know nothing about light-sensitive devices. The basic
idea is to replace the printhead on an old DECwriter with such a
device, then feed a photograph into it -- the computer will then
send a series of spaces to advance the head across the surface of
the photo, pausing to sense the grayscale value of each position.
The A/D conversion, computer interfacing, and software aspects
don't seem to present any particular problem. It's the analog
circuitry that I need help with.
So: o How do I choose a device ?
o How do I treat it: Physically -- mounting ???
Electrically -- support circuitry ???
o Is "aiming" critical -- if so, how do I do it ?
o Should I use just a detector, or an emitter/detector
pair ? If the latter, how do I power the emitter ?
(i.e.: continuous vs. pulsed)
BTW, the DECwriter I intend to use has minimum pitch settings
of 16.5/inch H x 12/inch V -- so the idea is to sense a sort
of "average" intensity from an area about 1/16" x 1/12".
Also, I recall seeing an article in some computer hardware hacker
magazine which described a project like this one. Does anyone
else remember seeing it ??? Does anybody remember the name of
the magazine, or the title of the article, or the date of the
issue, or anything like that ???
Thank You,
Kevin Crean ( ...!decvax!decwrl!dec-rhea!dec-ny1mm!crean )
Assoc. Software Specialist
DIGITAL Equipment Corp.
200 White Plains Rd.
Tarrytown, NY 10591
(914) 684-5721gnu@sun.uucp (John Gilmore) (06/05/85)
> The basic > idea is to replace the printhead on an old DECwriter with such a > device, then feed a photograph into it... There's already a product for Macintosh that does this with an Imagewriter. If you're interested in scanning in photographs, as opposed to having fun with building strange hardware, go that route. Look in a recent MacWorld magazine for an ad.
brian@sdcsvax.UUCP (Brian Kantor) (06/06/85)
A nifty way to do image-to-printer conversion is to buy one of the cheap tv scan converters that are made - we picked on up for $350, plugged it into an S-100 system that was sitting around, added a surplus tv camera, and now we can take just about any b&w image (photo, magazine, etc) and digitize it as 256x256x64. Take the 256 horizontal pixels, and produce 128 pixels (averaging them is a simple way), and then use them to look up a pattern in a table. A few years back in the Siggraph publications there was a table of densities (I think it was 256 levels, but I don't have it here to look at) that was achieved on a decwriter by overprinting up to four characters. There you have it, a printer picture. Now just use a film ribbon and wax paper, and you can iron it onto a T-shirt. Brian Kantor UC San Diego Computer Graphics Lab decvax\ brian@ucsd.arpa akgua >--- sdcsvax --- brian ucbvax/ Kantor@Nosc