[Blindmath] grayscale braille

Tue Mar 20 16:37:34 UTC 2012

I have been following this conversation with interest. For the record, I am
not blind and know very little about Braille. However, I do know quite a
lot about image processing.

In the sighted world, a character printer can definitely be used to produce
gray scale images, but not in the way that is described here.

In the 1960s, a typical data processing printer weighed several hundred
pounds, stood chest high from the floor, printed upper-case letters,
numbers, and a set of special characters at 10 characters per inch with a
line length of 132 characters on 14-inch wide fan-fold paper. A typical
data processing printer could print 600 lines per minute or more. With some
printers, the paper came out so fast that special mechanisms were required
to prevent it from flying across the room and to refold itself in the
output bin.

Many data centers had various examples of printer art posted on the walls
with the most common being a reasonably good gray scale replica of the Mona
Lisa.

However, unlike the scheme that is described here, there was no intent for
the viewer to assign special meaning to any individual character. In fact,
the intent was for the characters to visually run together is such a way
that they would not be perceived as characters at all. Instead, the big
picture view of the printout would give the impression of a gray scale
image with individual characters fading into the background.

Someone came up with a sequence of characters based on the amount of ink
deposited within the 0.1-inch wide cell by each character. That was a long
time ago and I don't recall the specific sequence of characters that was
used. I am guessing that the period character was used to convey light
gray. Moving from there through the sequence, each character deposited more
ink and therefore produced a darker cell. I'm also guessing that the
sequence probably consisted of eight to ten different characters making it
possible to produce the illusion of eight to ten levels of gray.

Characters were chosen such that when a person stepped away from the
printout and viewed it as a whole, that person didn't see individual
characters. Instead, the result was an illusion of a large gray scale image.

I used this scheme myself in the days before the invention of the CalComp
incremental plotter to produce images of contour maps.

Perhaps a similar scheme could be used with braille with each cell
containing from zero to six dots (or perhaps eight dots). This might make
it possible for a blind person to perceive white plus six (or eight) levels
of gray without the requirement to mentally associate specific characters
with specific shades of gray.

For the six-dot case, the following sequence of characters might provide
the illusion of increasing darkness (but a different selection might
produce better tactile results):

hex 41, A, 1 dot
hex 42, B, 2 dots
hex 44, D, 3 dots
hex 47, G, 4 dots
hex 51, Q, 5 dots
hex 3D, =, 6 dots

Dots have long been used to produce the illusion of gray scale images. When
I was a youngster, pictures in most small-town newspapers were presented in
gray scale because printing presses that could print in color were very
expensive. If you looked closely at a newspaper photo, you could see that
the picture was simply an array of dots. I seem to recall that the gray
scale effect was achieved by producing an array of black dots on a uniform
grid using different sized dots.

At one point in time, I had some very interesting photographs from "Life"
magazine involving very unique gray scale images. In those photos, a
photographer produced images of various things, including a portrait of
Woodrow Wilson and a picture of the U.S. Marine insignia by taking
photographs of thousands of troops in formation wearing white shirts and
black shirts. In effect, each person was one dot in the image.

Apparently the photographer would place the camera on top of a building or
tower and take of picture of the troops in formation down below. He even
took perspective into account. For example, moving away from the camera,
each row of troops was wider than the one before it. In some cases, the row
of troops closest to the camera contained 20 or 30 troops while the most
distant row would contain 200 to 300 troops. Thus, the "dot density"
increased as you viewed the image going from bottom to top.

I was able to find an image of a printer generated Mona Lisa on the web,
but was unable to find any images of the human-dot photographs.

Dick Baldwin

On Mon, Mar 19, 2012 at 6:13 PM, Michael Whapples <mwhapples at aim.com> wrote:

> I don't know if John is on the blindmath list, I'll forward the message on
> in case he isn't, however it would be better if you could somehow
> communicate direct with him (eg. by posting to the NFB-science list if he
> isn't on blindmath).
>
> Michael Whapples
>
> -----Original Message----- From: Pranav Lal
> Sent: Monday, March 19, 2012 10:58 PM
> To: 'Blind Math list for those interested in mathematics'
> Subject: Re: [Blindmath] grayscale braille
>
>
> Hi John,
>
> Can I use this plotting technique for any image? Your example seems to work
> only for functions.
>
> Pranav
>
>
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-- 
Richard G. Baldwin (Dick Baldwin)
Home of Baldwin's on-line Java Tutorials
http://www.DickBaldwin.com

Professor of Computer Information Technology
Austin Community College
(512) 223-4758
mailto:Baldwin at DickBaldwin.com
http://www.austincc.edu/baldwin/