[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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