/etc/ImageMagick-6/quantization-table.xml is in imagemagick-6-common 8:6.9.7.4+dfsg-16ubuntu6.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 | <?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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