Image to ASCII algorithms

Dear readers,

I am researching Image to ASCII conversion programmes, and I need some
help on the algorithms.
My intention is not to write a new image to ASCII conversion programme,
rather, I would like to learn about the background and about types of
algorithms and how long they have been around (70's, 80's 90's?). My
background is image processing.

Could someone shed some light on which algorithm is used in which
programme? Could someone send
me excerpts of the source? Please contact me directly if you are a
software author, and if you are uncomfortable talking about the precise
tricks or sending source code. I am sure we can work something out to
warrant your copyright, authorship and of course artistic originality.
Perhaps you could refer me to the experts, or point to algorithm
descriptions and specific source code? If I know where to find specific
source code, I would be able to hunt down the programme with more vigor!

Email me directly at big...@magma.ca. I will be happy to summarize
the findings and post it back to the news group.

For starts, I am unfamiliar with the programme internals, but I could
think of a few algorithms.

An image is split into M-by-N tiles (sub images) and then

1. the gray values for each tile is computed, and an M-by-N array of
ASCII characters is generated,
whereby for each tile the ASCII character that best matches the
grey-value is placed in the array; pre-calculated grey-values of
selected ASCII characters are used for the search, while the actual
ASCII character is used in the final composition;

or

2. as above, but now the bit map of the ASCII characters are used, not
just an overall grey-value;
the tile size (pixels) is made to match the the bit map size (pixels) by
image resizing (e.g. pixel averaging
or interpolation)

3. as above, but now more refined images of characters are used, not
just a binary bit map, and the images contain alternate backgrounds,
colors and  perhaps even different font types or font drawings; the
images ar used for the search as well as for the final composition.

I am posting this request since I know that there are some great non-PC
based programmes, and I
have no access to Unix or Linux to try them out. Also, I have had some
bad luck with web sites that
offer downloads of conversion programmes. The description and, if
possible, the source code of the
core algorithm is really all I would need to continue with my research.

Your input would be very valuable,

Thanks,

Aryan.

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