Re: richard heathfield
From: Arthur J. O'Dwyer (ajo_at_nospam.andrew.cmu.edu)
Date: 11/18/03
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Date: Mon, 17 Nov 2003 18:19:52 -0500 (EST)
On Mon, 17 Nov 2003, Mantorok Redgormor wrote:
>
> Richard Heathfield wrote...
> > Mantorok Redgormor wrote:
> > >
> > > Well I am still dying to know, how did you create that
> > > ascii art program? What is the technique you used?
> >
> > Er, let me think...
> >
> > Okay, I started off by taking a photograph of Clint, my debugging
> > teddybear. The photograph was in JPEG format. I transferred it to
> > my Linux box, where I used the GIMP to turn it into Windows bitmap
> > format (basically because bitmaps are easier to code for). I then
> > flipped it back over to Windows, and wrote a C++ Builder program to
> > load the bitmap into a canvas for me. That gave me pixel-by-pixel
> > access. Pause.
>
> I can convert it to (greyscale)bmp
Richard apparently used (one of the) RGB BMP format(s).
But greyscale works, given that ASCII art is greyscale. :)
> and then run it through hexdump
> not sure if this is good enough
No; you need to get the actual pixel values involved, not just
the bytes stored in the disk file. The most common formats
do have a one-to-one correspondence between bytes and pixels
(plus a file header), but easier to just load the image up and
manipulate the "pixel array" directly.
Blatant plug:
http://www.contrib.andrew.cmu.edu/~ajo/free-software/ImageFmtc.h
> > I also wrote another C++ Builder program. This one wrote the entire
> > printable subset of the character set onto a canvas, using a sensible
> > fixed-pitch font such as might be displayed by a console. It then did
> > pixel-counting to determine the "density" of each letter.
>
> Do you know of some documentation that explains the above in depth?
I could tell you how to do it in old MS-DOS, using the system ROM
default font. These days, you might see how your user is actually
going to view your image: e.g., in black-on-white Courier font.
Then figure out the format of TTF font images and proceed as above.
But that's hella complicated, IMHO. :-)
> > Back to the first program. :-) Okay, I iterated over the bitmap, using
> > square blocks of pixels, and averaging their red, green, and blue values to
> > get a final greyscale value. The program then decided which letter best
> > approximated that value (it wasn't difficult: letter[greyscalevalue / 4],
> > basically). And then it was all over bar the shouting. The shouting, in
> > this case, consisted of generating an ever-so-slightly non-obvious but 100%
> > standard ISO C program to display the actual characters.
>
> likewise for documentation. I am interested in doing this.
for each row in the image
for each pixel in the row
display Lookup(pixel value)
The details of 'Lookup' depend on how fancy you want to get.
A simple version of 'Lookup' would be
char Lookup(int p) {
return (p <= 127)? (' '): ('M');
}
A slightly more complicated (2-bit greyscale instead
of 1-bit) version would be
char Lookup(int p) {
char lu[] = " ;fM";
return lu[p/64];
}
Exercise: Extend this method to 8-bit greyscale.
Another way to do it would be to pass 'Lookup' whole
blocks of pixels, 2x2 or 4x3 blocks (depending on how
high-resolution or incredibly tiny you want to make your
ASCII art images):
for each pair of rows in the image
for each pair of pixels in the rows
display Lookup(top left pixel, top right pixel, bottom ...)
char Lookup(int p1, int p2, int p3, int p4)
{
char lu[] = " `'\"-!~r-~!7=t19.{/F:IfP+]j9zHZP"
".\}T+L[Y;5lTxSH9_LJXcL6EjbdGm6dM"
int ofs = 0;
ofs |= (p1 > 127) << 3;
ofs |= (p2 > 127) << 2;
ofs |= (p3 > 127) << 1;
ofs |= (p4 > 127) << 0;
return lu[ofs];
}
This is where the serious font-processing comes in, the stuff
that I could tell you about for DOS but not Windows and certainly
not for Linux.
Everything else is just sugarcoating.
[Historical interest: Before ASCII art, there was "typewriter
art," that was meant to be typed on a typewriter (including the
backspace action, for example). Anyone know if anyone ever
tried multicolored typewriter art -- one text per primary color?]
-Arthur
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