Question

how do i convert an image represented as double into an image that i can use to produce a histogram?

(with dohist:)

% computes the histogram of a given image into num bins.
% values less than 0 go into bin 1, values bigger than 255
% go into bin 255
% if show=0, then do not show. Otherwise show in figure(show)


function thehist = dohist(theimage,show)

  % set up bin edges for histogram

  edges = zeros(256,1);
  for i = 1 : 256;
    edges(i) = i-1;
  end

  [R,C] = size(theimage);
  imagevec = reshape(theimage,1,R*C);      % turn image into long array
  thehist = histc(imagevec,edges)';        % do histogram

  if show > 0
      figure(show)
      clf
      pause(0.1)
      plot(thehist)
      axis([0, 256, 0, 1.1*max(thehist)])
  end

Answer 1

I am guessing that you just need to normalize your image first, to do this you can use:

255*(theimage./(max(theimage(:)));