[accessibleimage] Re: Deposition, pixel density and Braille dot shape

Hello Joshua,

We have done a lot of work in this area, to find out more you can visit our
website

www.timp.org.uk

But to briefly try to answer some of your questions.

1.  We typically print at 180 x 360 dpi as we this suits our production
process well and offers a good level of detail.  We have gone down to 90 x
90 dpi with minimal aparent loss of discernability of feature.  I would
imagine that most ink-jet deposition processes would have an inherent dpi
higher than 90.

2. We are investigating this issue of the shapes of Braille dots (or
profile) currently.  Up till now this has been very much a factor of the
production method used, though a deposition process should offer some degree
of versatility and more control.  It could be argued that a smooth dome
shape offers greater comfort and readability, yet a square edged cylinder
might offer more sharpness. There is some interesting work being done in
Poland on this by Dr Ludwik Buczynski. We are interested in the
3-dimensional profile of all point, line and area tactile symbols, not just
Braille. I think it is still to be ascertained how much value can be gained
from enhanced line profiles.  I would be very interested in any comments on
this.

3.  In theory yes.  One greyscale print-head I know of has 8 levels of grey
firing 0 millilitres (white), 8, 16, 24, 32, 40, 48, 56 and 64 (black) of
ink.  So the more litres of ink being deposited, the higher and, depending
of flow, wider the dot.  But given that most deposition processes seem to be
multi-pass, a binary (white or black) print engine acheives a variation in
height by varying the number of passes.

4.  The pixel density is dependant on the print-head within the machine.  If
you know the make and type of print-head it should be easy to find the
inherent density - the actual number and spacing of nozzles from where the
ink or wax is ejected. Most manufacturers are creative in their claims of
print density.  For example a printer that says printing at 1440 dpi on the
box is most likely to have a 360dpi print-head that prints four passes
slightly offset.

Feel ree to get in touch if you want to talk any of this over

Kind Regards

Don


****************************************
Don McCallum
Anglia Polytechnic University

Mob +44 7932 812 874
Work +44 1223 363 271 x2662

d.j.mccallum@xxxxxxxxx
****************************************




-----Original Message-----
From: accessibleimage-bounce@xxxxxxxxxxxxx
[mailto:accessibleimage-bounce@xxxxxxxxxxxxx]On Behalf Of Joshua A.
Miele
Sent: 23 April 2004 01:13
To: accessibleimage@xxxxxxxxxxxxx
Subject: [accessibleimage] Deposition, pixel density and Braille dot
shape


Hi, all.

I have several questions about how one would properly prepare a bitmap
image for production by the wax/ink deposition process such as is (i
believe) used by Tactile Vision, Braille Jymico, and probably others.
Assuming I wanted to prepare an 8-bit gray-scale  bitmap that is
"printer-ready," what attributes would that bitmap need? Specifically:

1. What is the minimum pixel density (say, pixels per inch) required for
producing good-quality Braille dots with this process?
2. what shape of Braille dots is best produced by the process: domes,
cones, square-edged cylinders, etc?
3. Is dot/line height on the output linearly related to the value of the
pixel in the gray-scale image?
4. What is the maximum pixel density of the machine itself?

Looking forward to hearing from anybody who can help me with these
questions. Thanks!

--JAM

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