Fine index matrix of an image

Let I be an image of m×n pixels, and M be the number of distinct colors. I can be
represented as I(x, y) = P(I'(x, y)), where P = {S1, S2, . . . , SM} is the set of all the
colors in I, and I' is a m×n matrix of indexes in {1, 2, . . . ,M} with M typically equal
to 256 or 512.

How to find the I' in an image

Answer 1

[Walter Roberson]

rgb2ind()

[Anusha]

rgb2ind(V);

Error using rgb2ind>parse_inputs (line 129)

RGB2IND(RGB) is a deprecated syntax.

Specify number of colors, tolerance, or colormap.

Error in rgb2ind (line 50)

[RGB,m,dith] = parse_inputs(varargin{:});

[Walter Roberson]

I didn't say to call it with only one argument.

I quote you,

and M be the number of distinct colors.

if you know the number of distinct colors, then re-read the rgb2ind() documentation.