Re: xPLRioNet - A Challenge

["Mark Harrison (Groups)" <mph@xxxxxxxxxxxxxxx>]

Tony Tofts wrote:

>Hi all,
>
>While coding up routines to handle the riot display for the Rio in
xplrionet
>I thought it would be a bit of fun to include the ability to render an
image
>onto the rio's screen...
>
>I'm currently looking at a Rio which is displaying an Album cover ;-)
>
>Problem is the conversion from colour bitmap to pure black and white
(not
>grey scale) isn't great.
>
>I'm currently taking a pass thru the bitmap, taking an average of the
RGB
>per pixel, and then an overall average.
>
>Then when rendering if the total of rgb < than the average it's
black, else
>it's white.
>
>But I think it could be a lot better. I believe you have to do stuff
like
>giving each RGB part a different weighting?
>
>So the challenge is... Can someone find a (not too complicated) formula
to
>give a decent image please?
>
>Many thanks
>Tony
>

Tony,

One option might be to use a half-toning approach with a 2x2 dither,
rather than pixel-mapping.

In case I'm talking pure babble, the concept is that rather than using
individual pixels and making unitary decisions on each, you divide the
display area into 2x2 arrays, and treat each array as having a choice of
5 intensity levels (0 = no pixels, 1 = top left pixel only, 2 = top left
and bottom right pixels, 3 = top left, top right, and bottom right
pixels, 4 = all four pixels.)

I guess that the problem you're up against is that most of the work in
this space has been on dealing with low colour depth in areas where you
have high definition available. Hence, beyond 2x2 arrays, you get into
much larger arrays, and deal with issues like dispersal of the "on
dots"
within each array. On a Rio screen, it's hard to believe that any array
larger than 2x2 would be useful.

TBH, I've no idea how it would look on a screen like the Rio's, but
that's what I'd do :-)

If you want a more detailed analysis, a search for "Floyd Steinberg
error diffusion" will probably help.

Regards,

Mark, who actually studied this stuff about 12 years ago :-)


xPL Links: http://www.xplproject.org.uk http://www.xplhal.com http://www.xpl.myby.co.uk
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