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Work around jpegtran to get correct rotated crops. #82

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Nov 12, 2020
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Work around jpegtran to get correct rotated crops. #82

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13 changes: 10 additions & 3 deletions cropgui_common.py
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Original file line number Diff line number Diff line change
Expand Up @@ -69,9 +69,16 @@ def get_cropspec(image, corners, rotation):
t, l, r, b = corners
w = r - l
h = b - t
# Technically this should produce perfect crops, but jpegtran is broken
# and so mistakenly rounds out fractional crops on flipped images. Sigh.
return "%dx%d+%d+%d" % (w, h, l, t)
# Technically these parameters should straightforwardly produce perfect
# crops, but jpegtran is broken here in two regards: (1) it doesn't
# recognise perfect rotated crops as such, so the '-perfect' switch
# erroneously rejects correctly ICMU-aligned rotate-and-crop commands, and
# (2) it mistakenly rounds out crops on rotated/flipped images so that even
# the bottom right corner is ICMU-aligned. Sigh. Adding the 'f' suffixes
# to the dimensions here at least solves (2), and seems to produce the same
# results as you get by manually constructing a pipeline of '-perfect'
# command lines.
return "%dfx%df+%d+%d" % (w, h, l, t)


def ncpus():
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9 changes: 5 additions & 4 deletions generate_test_images.sh
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Expand Up @@ -5,11 +5,12 @@
dir=test
[ -d $dir ] || mkdir $dir

text='-density 72 -pointsize 32 -weight Bold -gravity NorthWest -fill rgba(255,0,0,0.5) -annotate +0+0 A -annotate +32+32 B -annotate +64+64 C -annotate +96+96 D -annotate +128+128 E -annotate +160+160 F -annotate +192+192 G -annotate +224+224 H -annotate +256+256 I -annotate +288+288 J -annotate +320+320 K -fill rgba(0,255,0,0.5) -annotate +352+352 L -annotate +384+320 M -annotate +416+288 N -annotate +448+256 O -annotate +480+224 P -annotate +512+192 Q -annotate +544+160 R -annotate +576+128 S -annotate +608+96 T -annotate +640+64 U -annotate +672+32 V -fill rgba(0,0,255,0.5) -annotate +704+0 W -annotate +736+32 X -annotate +768+64 Y'
convert -size 100x100 pattern:gray50 -scale 1600% -sampling-factor 2x2 \
-crop 796x396+0+0 $dir/chess-2x2.jpg
-crop 796x396+0+0 $text $dir/chess-2x2.jpg
convert -size 100x100 pattern:gray50 -scale 800%x1600% -sampling-factor 1x2 \
-crop 796x396+0+0 $dir/chess-1x2.jpg
-crop 796x396+0+0 $text $dir/chess-1x2.jpg
convert -size 100x100 pattern:gray50 -scale 1600%x800% -sampling-factor 2x1 \
-crop 796x396+0+0 $dir/chess-2x1.jpg
-crop 796x396+0+0 $text $dir/chess-2x1.jpg
convert -size 100x100 pattern:gray50 -scale 800% -sampling-factor 1x1 \
-crop 796x396+0+0 $dir/chess-1x1.jpg
-crop 796x396+0+0 $text $dir/chess-1x1.jpg