■http://q.hatena.ne.jp/1408437001

~/hatena/q1408437001% sh batch.sh cat.jpg glenn.jpg london.jpg virgo.jpg

jpeg run with "cjpeg -quality 30 w.pnm > t.jpg" & "djpeg t.jpg > w.pnm"

#1 cat1.diff.png: mean 658.499

#10 cat10.diff.png: mean 0

#100 cat100.diff.png: mean 0

#1000 cat1000.diff.png: mean 0

im run with "convert w.pnm -quality 15 t.jpg" & "convert t.jpg w.pnm"

#1 cat1.diff.png: mean 1012.47

#10 cat10.diff.png: mean 0

#100 cat100.diff.png: mean 0

#1000 cat1000.diff.png: mean 0

j2k run with "opj_compress -r 400 -i w.pnm -o t.jpg.j2k > /dev/null 2>&1" & "opj_decompress -i t.jpg.j2k -o w.pnm > /dev/null 2>&1 ; mv t.jpg.j2k t.jpg"

#1 cat1.diff.png: mean 852.046

#10 cat10.diff.png: mean 153.899

#100 cat100.diff.png: mean 0

#1000 cat1000.diff.png: mean 0

jpeg run with "cjpeg -quality 30 w.pnm > t.jpg" & "djpeg t.jpg > w.pnm"

#1 glenn1.diff.png: mean 3399.9

#10 glenn10.diff.png: mean 13.1817

#100 glenn100.diff.png: mean 0

#1000 glenn1000.diff.png: mean 0

im run with "convert w.pnm -quality 15 t.jpg" & "convert t.jpg w.pnm"

#1 glenn1.diff.png: mean 3774.37

#10 glenn10.diff.png: mean 2.9123

#100 glenn100.diff.png: mean 0

#1000 glenn1000.diff.png: mean 0

j2k run with "opj_compress -r 400 -i w.pnm -o t.jpg.j2k > /dev/null 2>&1" & "opj_decompress -i t.jpg.j2k -o w.pnm > /dev/null 2>&1 ; mv t.jpg.j2k t.jpg"

#1 glenn1.diff.png: mean 5124.25

#10 glenn10.diff.png: mean 34.9354

#100 glenn100.diff.png: mean 0.54037

#1000 glenn1000.diff.png: mean 0

jpeg run with "cjpeg -quality 30 w.pnm > t.jpg" & "djpeg t.jpg > w.pnm"

#1 london1.diff.png: mean 1145.86

#10 london10.diff.png: mean 2.94233

#100 london100.diff.png: mean 0

#1000 london1000.diff.png: mean 0

im run with "convert w.pnm -quality 15 t.jpg" & "convert t.jpg w.pnm"

#1 london1.diff.png: mean 1589.42

#10 london10.diff.png: mean 0.262741

#100 london100.diff.png: mean 0

#1000 london1000.diff.png: mean 0

j2k run with "opj_compress -r 400 -i w.pnm -o t.jpg.j2k > /dev/null 2>&1" & "opj_decompress -i t.jpg.j2k -o w.pnm > /dev/null 2>&1 ; mv t.jpg.j2k t.jpg"

#1 london1.diff.png: mean 1874.1

#10 london10.diff.png: mean 34.7301

#100 london100.diff.png: mean 0

#1000 london1000.diff.png: mean 0

jpeg run with "cjpeg -quality 30 w.pnm > t.jpg" & "djpeg t.jpg > w.pnm"

#1 virgo1.diff.png: mean 655.998

#10 virgo10.diff.png: mean 0.593173

#100 virgo100.diff.png: mean 0

#1000 virgo1000.diff.png: mean 0

im run with "convert w.pnm -quality 15 t.jpg" & "convert t.jpg w.pnm"

#1 virgo1.diff.png: mean 967.051

#10 virgo10.diff.png: mean 0.276289

#100 virgo100.diff.png: mean 0

#1000 virgo1000.diff.png: mean 0

j2k run with "opj_compress -r 400 -i w.pnm -o t.jpg.j2k > /dev/null 2>&1" & "opj_decompress -i t.jpg.j2k -o w.pnm > /dev/null 2>&1 ; mv t.jpg.j2k t.jpg"

#1 virgo1.diff.png: mean 689.347

#10 virgo10.diff.png: mean 72.9174

#100 virgo100.diff.png: mean 55.549

#1000 virgo1000.diff.png: mean 145.837

追記：quality 95でも行った。収束は遅くなるが100回までで収束した。

jpeg95 run with "cjpeg -quality 95 w.pnm > t.jpg" & "djpeg t.jpg > w.pnm"

#1 cat1.diff.png: mean 59.3537

#10 cat10.diff.png: mean 9.35999

#100 cat100.diff.png: mean 0

#1000 cat1000.diff.png: mean 0

jpeg95 run with "cjpeg -quality 95 w.pnm > t.jpg" & "djpeg t.jpg > w.pnm"

#1 glenn1.diff.png: mean 2104.51

#10 glenn10.diff.png: mean 69.472

#100 glenn100.diff.png: mean 10.8727

#1000 glenn1000.diff.png: mean 0

jpeg95 run with "cjpeg -quality 95 w.pnm > t.jpg" & "djpeg t.jpg > w.pnm"

#1 london1.diff.png: mean 79.604

#10 london10.diff.png: mean 80.2684

#100 london100.diff.png: mean 8.79387

#1000 london1000.diff.png: mean 0

jpeg95 run with "cjpeg -quality 95 w.pnm > t.jpg" & "djpeg t.jpg > w.pnm"

#1 virgo1.diff.png: mean 213.594

#10 virgo10.diff.png: mean 11.7891

#100 virgo100.diff.png: mean 0.00817928

#1000 virgo1000.diff.png: mean 0

~/hatena/q1408437001% cat batch.sh

#/bin/sh
work=w.pnm
temp=t.jpg
list="jpeg im j2k"
enc_jpeg="cjpeg -quality 30 $work > $temp"
dec_jpeg="djpeg $temp > $work"
enc_im="convert $work -quality 15 $temp"
dec_im="convert $temp $work"
enc_j2k="opj_compress -r 400 -i $work -o $temp.j2k > /dev/null 2>&1"
dec_j2k="opj_decompress -i $temp.j2k -o $work > /dev/null 2>&1 ; mv $temp.j2k $temp"

for orig in "$@" ; do
	for name in $list ; do
		eval enc=\$enc_$name
		eval dec=\$dec_$name
		if [ "x$enc" == x -o "x$dec" == x ] ; then continue ; fi
		echo $name run with  \"$enc\" "&" \"$dec\" || continue
		mkdir $name > /dev/null 2>&1
		chdir $name || contimue
		convert ../$orig $work || return 1
		i=0
		before=../$orig
		for c in 1 10 100 1000 ; do
			while [ $i -lt $c ] ; do
				eval $enc && \
				eval $dec && \
				i=$((i+1)) || break
			done
			base=${orig%.*}${i}
			cp $temp ${base}.jpg
			convert $work ${base}.png
			composite $before ${base}.png -compose difference ${base}.diff.png
			echo -n "#$i "
			identify -format '%f: mean %[mean]\n' ${base}.diff.png
			before=${base}.png
		done
		chdir .. || return 1
	done
done

サンプルデータの元は下記を使用

cat.jpg

http://f.hatena.ne.jp/SQB/20140823171814

glenn.jpg

https://www.flickr.com/photos/nasacommons/9417092314/?rb=1

london.jpg

http://f.hatena.ne.jp/SQB/20140823144943

virgo.jpg

https://www.flickr.com/photos/stuutje/14970601715/?rb=1

コーデックは下記を使用

jpeg

cjpeg & djpeg, The Independent JPEG Group's, var.8d, http://www.ijg.org/

im

convert, ImageMagick, ver.6.8.9-4, http://www.imagemagick.org/

j2k

opj_compress & opj_decompress, The OpenJPEG library, var.2.1.0, https://code.google.com/p/openjpeg/

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