imagemagick - return the bounding box of each contiguous object

Question

How do you use imagemagick to return the bounding box coordinates of each object identified in the image?

Answer 1

You can do that in Imagemagick using connected components processing. The following is Unix syntax for Imagemagick 6

Read the input. Then threshold and add some padding. Then apply morphology close to close up some disconnected regions that should connect (especially the bone on the head) and shave off the padding. Then apply connected components processing.

convert objects.jpg \
-negate -threshold 15% -bordercolor black -border 10 \
-morphology close disk:8 -type bilevel -shave 10x10 \
-define connected-components:exclude-header=true \
-define connected-components:mean-color=true \
-define connected-components:area-threshold=100 \
-define connected-components:verbose=true \
-connected-components 8 null: | grep "gray(255)" | awk '{ print $2 }'

Result Listed To Terminal Window:

268x567+408+35
212x379+185+48
560x98+2+652
75x434+36+5
128x131+26+460
128x130+231+498

list="268x567+408+35
212x379+185+48
560x98+2+652
75x434+36+5
128x131+26+460
128x130+231+498"
convert objects.jpg tmp.png
for item in $list; do
ww=`echo "$item" | tr "x" "+" | cut -d+ -f1`
hh=`echo "$item" | tr "x" "+" | cut -d+ -f2`
xo=`echo "$item" | tr "x" "+" | cut -d+ -f3`
yo=`echo "$item" | tr "x" "+" | cut -d+ -f4`
x1=$xo
y1=$yo
x2=$((x1+ww))
y2=$((y1+hh))
convert tmp.png -fill none -stroke red \
-draw "rectangle $x1,$y1 $x2,$y2" -alpha off tmp.png
done
convert tmp.png objects_bboxes.jpg
rm -f tmp.png