Re: Anybody have a prgram to write a .bmp file?

[Paul Kienzle]

On Feb 6, 2007, at 11:19 AM, Robert A. Macy wrote:

> Paul,
>
> I don't understand what you said.
>
> The X index matrix is square, the same siaxe as the r,g,b
> matrices, and consists of integers going from one up to the
> total size of the matrix: rows*columns
>
> The map is the similar size of
>   rows*columns by 3
> and the values in the matrix are between 0 and 1

yes

> colourmap appears to be 64 by 3 no matter what I do, even
> if I clear the thing, it comes back after
> > > [X,map]=rgb2ind(r,g,b);

yes

> It sounds like you're trying to limit the color from 24 bit
> down to 256 color, but how do I do that using these
> functions?

When you do bmpwrite(X,map,'file') it is trying to
use a map of length 65536, but bmpwrite only
supports a map of length 256.

You can:

(a) detect if the map is of length greater than 256
and write a truecolor image instead,

(b) backport the bmpwrite from octave-forge CVS so
that you can writing truecolor rgb maps directly, or

(c) fix rgb2ind so that it finds the best map of
length 256 with which to represent the colors.  I
suggested using a perceptual quantization rather than
an rgb quantization to make better use of the map.

I've implemented option (a) in the attached file.

- Paul

bmpwrite.m
Description: Binary data