title: how to do histogram for dct coeffcient to show Double Quantiztion effect?
body: <p>what i want to do is a histogram for quantized DCT coefficient for an image, to detect Double Quantization effect. when i use hist(x) it will categorize it in to 10s and if i changed it to hist(x,20) or 30 it does not really show the DQ effect. so is there any better way for this??
  here is the code: on matlab</p>
  
  <pre><code>im = jpeg_read('image');
  % Pull image information - Lum, Cb, Cr
  lum = im.coef_arrays{im.comp_info(1).component_id};
  cb = im.coef_arrays{im.comp_info(2).component_id};
  cr = im.coef_arrays{im.comp_info(3).component_id};
  % Pull quantization arrays
  lqtable = im.quant_tables{im.comp_info(1).quant_tbl_no};
  cqtable = im.quant_tables{im.comp_info(2).quant_tbl_no};
  % Quantize above two sets of information
  qcof = quantize(lum,lqtable);
  bqcof = quantize(cb,cqtable);
  rqcof = quantize(cr,cqtable);
  hist(qcof,30); %lum quantized dct coefficient histogram
  </code></pre>