Implement PixelRegion option for imread(). * imread.m: document new option. * private/__imread__.m: parse new option and set defaults. * __magick_read__.cc (calculate region): new option to calculate the region to be read, shifts in memory required, and output image size. (read_indexed_images, read_images): implement reading of only specific regions of an image. (__magick_read__): get octave_scalar_map at start for simplicity.

#include "mex.h"

void
mexFunction (int nlhs, mxArray* plhs[],
             int nrhs, const mxArray* prhs[])
{
  mwSize n;
  mwIndex i;

  if (nrhs != 1 || ! mxIsCell (prhs[0]))
    mexErrMsgTxt ("ARG1 must be a cell");

  n = mxGetNumberOfElements (prhs[0]);
  n = (n > nlhs ? nlhs : n);
  
  for (i = 0; i < n; i++)
    plhs[i] = mxDuplicateArray (mxGetCell (prhs[0], i));
}