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Editing File: /etc/ImageMagick-6/quantization-table.xml

<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE quantization-tables [
<!ELEMENT quantization-tables (table)+>
<!ELEMENT table (description , levels)>
<!ELEMENT description (CDATA)>
<!ELEMENT levels (CDATA)>
<!ATTLIST table slot ID #REQUIRED>
<!ATTLIST levels width CDATA #REQUIRED>
<!ATTLIST levels height CDATA #REQUIRED>
<!ATTLIST levels divisor CDATA #REQUIRED>
]>
<!--
  JPEG quantization table created by Dr. Nicolas Robidoux, Senior Research
  Scientist at Phase One (www.phaseone.com) for use with 2x2 Chroma
  subsampling and (IJG-style, hence ImageMagick-style) quality level
  around 75.

It is based on the one recommended in

Relevance of human vision to JPEG-DCT compression by Stanley A. Klein,
    Amnon D. Silverstein and Thom Carney. In Human Vision, Visual
    Processing and Digital Display III, 1992.

for 1 minute per pixel viewing.

Specifying only one table in this xml file has two effects when used with
  the ImageMagick option
  
    -define jpeg:q-table=PATH/TO/THIS/FILE
  
  1) This quantization table is automatically used for all three channels;

2) Only one copy is embedded in the JPG file, which saves a few bits
     (only worthwhile for very small thumbnails).
-->
<quantization-tables>
  <table slot="0" alias="luma">
    <description>Luma Quantization Table</description>
    <levels width="8" height="8" divisor="1">
      16,  16,  16,  18,  25,  37,  56,  85,
      16,  17,  20,  27,  34,  40,  53,  75,
      16,  20,  24,  31,  43,  62,  91,  135,
      18,  27,  31,  40,  53,  74,  106, 156,
      25,  34,  43,  53,  69,  94,  131, 189,
      37,  40,  62,  74,  94,  124, 169, 238,
      56,  53,  91,  106, 131, 169, 226, 311,
      85,  75,  135, 156, 189, 238, 311, 418
    </levels>
  </table>
<!--
  If you want to use a different quantization table for Chroma (say), just add

<table slot="1" alias="chroma">
    <description>Chroma Quantization Table</description>
    INSERT 64 POSITIVE INTEGERS HERE, COMMA-SEPARATED
    </levels>
  </table>

here (but outside of these comments).
-->
</quantization-tables>

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