(simple) webcam image analysis

Here I present simple webcam image analysis and it's variation in time.

Intro

I have a webcam, connected to my Raspberry Pi server. Photos are taken every five minutes with fswebcam. Such collection of photos you can use for creating eg. time lapse video (here is an example of one-day video taken from my window). But you can also perform an analysis of image composition and it's variation over time.

Howto

Gathering data

Wen we have photos taken during a day gargered in one directory, we can use a simple script to analyse subsequent frames. ImageMagick is used to convert photos to 1x1 px size and get their HSB and RGB values.

#!/bin/bash

OUT=webcam.dat

echo "#i        h       s       v       r       g       b" > $OUT

for image in *.jpg
do

((i++))

hsb=`convert "$image" -colorspace hsb  -resize 1x1  txt:- | sed 1d  | tr '()%,:' ' '`

h=`echo $hsb | awk '{print $8}'`
s=`echo $hsb | awk '{print $9}'`
v=`echo $hsb | awk '{print $10}'`

rgb=`convert "$image" -colorspace rgb  -resize 1x1  txt:- | sed 1d  | tr '()%,:' ' '`

r=`echo $rgb | awk '{print $3}'`
g=`echo $rgb | awk '{print $4}'`
b=`echo $rgb | awk '{print $5}'`

echo "$i        $h      $s      $v      $r      $g      $b" >> $OUT

done

Data visualisation

Then we use a gnuplot script to get pretty plots:

set pointsize 2
# Line style for axes
set style line 80 lt rgb "#808080"
# Line style for grid
set style line 81 lt 0  # dashed
set style line 81 lt rgb "#808080"  # grey
set grid back linestyle 81
set border 3 back linestyle 80
set xtics nomirror
set ytics nomirror
set xlabel "frame number"
set terminal png nocrop enhanced font "Gill Sans,8" size 700,500

plik='webcam.dat'

set ylabel "HSB [%]"

set output "out/hsv-csplines.png"
plot plik using 1:2 smooth csplines title "Hue" lt rgb "red" lw 1,\
plik using 1:3 smooth csplines title "Saturation" lt rgb "green" lw 1,\
plik using 1:4 smooth csplines title "Brightness" lt rgb "blue" lw 1

set output "out/hsv-bezier.png"
plot plik using 1:2 smooth bezier title "Hue" lt rgb "red" lw 1,\
plik using 1:3 smooth bezier title "Saturation" lt rgb "green" lw 1,\
plik using 1:4 smooth bezier title "Brightness" lt rgb "blue" lw 1

set ylabel "RGB"

set output "out/rgb-csplines.png"
plot plik using 1:5 smooth csplines title "Red" lt rgb "red" lw 1,\
plik using 1:6 smooth csplines title "Green" lt rgb "green" lw 1,\
plik using 1:7 smooth csplines title "Blue" lt rgb "blue" lw 1

set output "out/rgb-bezier.png"
plot plik using 1:5 smooth bezier title "Red" lt rgb "red" lw 1,\
plik using 1:6 smooth bezier title "Green" lt rgb "green" lw 1,\
plik using 1:7 smooth bezier title "Blue" lt rgb "blue" lw 1

Output: plots

HSB, with different methods of curves smoothing

 

RGB, with different methods of curves smoothing

 

Live monitoring

To get the plots almost live, we can use rrdtool to gather, store and plot those data. First, create rrd database:

#!/bin/bash
rrdtool create hsb-rgb.rrd \
--step 300 \
DS:h:GAUGE:600:0:100 \
DS:s:GAUGE:600:0:100 \
DS:j:GAUGE:600:0:100 \
DS:r:GAUGE:600:0:255 \
DS:g:GAUGE:600:0:255 \
DS:b:GAUGE:600:0:255 \
RRA:AVERAGE:0.5:1:288                   \
RRA:AVERAGE:0.5:6:336                   \
RRA:AVERAGE:0.5:24:732                  \
RRA:AVERAGE:0.5:144:14600       \
RRA:MIN:0.5:1:288                       \
RRA:MIN:0.5:6:336                       \
RRA:MIN:0.5:24:732                      \
RRA:MIN:0.5:144:14600   \
RRA:MAX:0.5:1:288                       \
RRA:MAX:0.5:6:336                       \
RRA:MAX:0.5:24:732                      \
RRA:MAX:0.5:144:14600

Then add such lines to your webcam script (launched from cron every 5 minutes). $OUT_FILE is variable pointing to a just taken photo.

hsb=`convert "$OUT_FILE" -colorspace hsb  -resize 1x1  txt:- | sed 1d  | tr '()%,:' ' '`

h=`echo $hsb | awk '{print $8}'`
s=`echo $hsb | awk '{print $9}'`
v=`echo $hsb | awk '{print $10}'`

rgb=`convert "$OUT_FILE" -colorspace rgb  -resize 1x1  txt:- | sed 1d  | tr '()%,:' ' '`

r=`echo $rgb | awk '{print $3}'`
g=`echo $rgb | awk '{print $4}'`
b=`echo $rgb | awk '{print $5}'`

# update rrd database:
rrdtool update hsb-rgb.rrd "N:$h:$s:$v:$r:$g:$b"

Finally, after some data are collected, we can plot a nice graph (actually, we can plot it every five minutes, as new data arrives):

#!/bin/bash

BAZA=hsb-rgb.rrd

rrdtool graph hsb-24h.png  \
        --imgformat PNG \
        --start "now-24h"\
        --title="HSB [%]"       \
        --height 240    \
        --width 420    \
        --lazy \
        --alt-autoscale \
        --alt-y-grid \
        DEF:h=$BAZA:h:AVERAGE \
        DEF:s=$BAZA:s:AVERAGE \
        DEF:j=$BAZA:j:AVERAGE \
        LINE2:h#FF0000:"Hue"\
        LINE2:s#00FF00:"Saturation"\
        LINE2:j#0000FF:"Brightness"</pre>
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjFCZoyRIhEXYQEgSiiI3RGEZFtSfnJog6hNDprEf8JzjU7_1v8DCDAnxSUuxBcq3tqSYGJkfdr4UoZ2rHV-BBREHFU8KE4Flnob8XnD7_5PhWOzuxG9B8sidzWmhX8PGtMGFU0Rlo_l7XL/s1600/HSB-24h.png" imageanchor="1" ><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjFCZoyRIhEXYQEgSiiI3RGEZFtSfnJog6hNDprEf8JzjU7_1v8DCDAnxSUuxBcq3tqSYGJkfdr4UoZ2rHV-BBREHFU8KE4Flnob8XnD7_5PhWOzuxG9B8sidzWmhX8PGtMGFU0Rlo_l7XL/s320/HSB-24h.png" /></a><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhyGserUs6dUyqdudZA5_UagqTuZTj_weClykD_LKd_6ENAYSKw5tuqsugFVGbGH73rxJAH1kDhs2dCF_DBLB_H_dxZsD6k7XRRYFcdzP9uVgJKxIdA675z53hNIAeX0BXE2UsswMLBRK9D/s1600/RGB-24h.png" imageanchor="1" ><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhyGserUs6dUyqdudZA5_UagqTuZTj_weClykD_LKd_6ENAYSKw5tuqsugFVGbGH73rxJAH1kDhs2dCF_DBLB_H_dxZsD6k7XRRYFcdzP9uVgJKxIdA675z53hNIAeX0BXE2UsswMLBRK9D/s320/RGB-24h.png" /></a>

Conclusions

I don't know, if this makes any sense, but looks cool :)