getting a specific indicator on an image with imagemagick -

i'd evaluate if picture blurred or not. using imagemagick 6.7.7-10 i've seen identify commmand gives interesting information, , command:

identify  -format "%[filename] sd:%[standard-deviation]\n" floue1.jpg 

answer> floue1.jpg sd:7876.9

seems start. however, if use:

identify -verbose floue1.jpg | grep stan    standard deviation: 34.8189 (0.136545)   standard deviation: 26.7428 (0.104874)   standard deviation: 29.8434 (0.117033)   standard deviation: 30.6494 (0.120194) 

i see 4 standard deviation values,one global , 1 each color channel, , these values differ single 1 got first command.

where these results come from/mean, , how can select (print) of these?

it works this:

identify -verbose floue1.jpg | grep stan   standard deviation: 39.0047 (0.15296)   standard deviation: 36.45 (0.142941)   standard deviation: 37.9805 (0.148943)   standard deviation: 37.8263 (0.148339) 

the first number on line scaled on range 0-255 , second 1 normalised range of 0 1.

the first row red standard deviation, second green , third blue, whereas last averaged on channels.

if want access them individually, use:

convert floue1.jpg -format "%[filename] sd:%[fx:standard_deviation.blue]\n" info: floue1.jpg sd:0.148943 

or, can select different 1 , scale too:

convert floue1.jpg -format "%[filename] sd:%[fx:int(standard_deviation.green*255)]\n" info: floue1.jpg sd:36 

if want them in 1 go , using bash, can do:

read sdr sdg sdb <<< $(convert floue1.jpg -format "%[fx:int(standard_deviation.red*255)] %[fx:int(standard_deviation.green*255)] %[fx:int(standard_deviation.blue*255)]" info: )  echo $sdr, $sdg, $sdb 39, 36, 37