Extract part of an image to identify

Question

I try to get verbose information about a part of an image. I read the doc of imageMagick and as far as I understand it, it should be possible to call identify with the -extract option. But, when I call it, I got an error message: 'unrecognized option: -extract'.

This is my commandline call identify -verbose -extract 20x20+0+20 ./mosaicTemplate.jpg

Does anyone knows, what is wrong with my commandline Call or has an convenient workaround?

Thanks in advance! Simon

score 2 · Accepted Answer · answered Nov 06 '15 at 10:11

Create a test image like this:

convert -size 500x500 gradient:red-blue image.png

Now check details of top left corner where image is pretty red:

convert image.png -crop 20x20+0+0 -verbose info:

Image: image.png
  Format: PNG (Portable Network Graphics)
  Mime type: image/png
  Class: DirectClass
  Geometry: 20x20+0+0
  Units: Undefined
  Type: Palette
  Endianess: Undefined
  Colorspace: sRGB
  Depth: 16-bit
  Channel depth:
    red: 16-bit
    green: 1-bit
    blue: 16-bit
  Channel statistics:
    Pixels: 400
    Red:
      min: 63040 (0.961929)
      max: 65535 (1)
      mean: 64287.3 (0.980962)                    <--- very red
      standard deviation: 757.295 (0.0115556)
      kurtosis: -1.20609
      skewness: 0.000125086
      entropy: 1
    Green:
      min: 0 (0)
      max: 0 (0)
      mean: 0 (0)
      standard deviation: 0 (0)
      kurtosis: 0
      skewness: 0
      entropy: nan
    Blue:
      min: 0 (0)
      max: 2495 (0.0380713)
      mean: 1247.65 (0.0190379)              <--- not very blue
      standard deviation: 757.295 (0.0115556)
      kurtosis: -1.20609
      skewness: -0.000125086
      entropy: 1

Now check details of bottom left corner where it is more blue:

convert image.png -crop 20x20+0+480 -verbose info:

Image: image.png
  Format: PNG (Portable Network Graphics)
  Mime type: image/png
  Class: DirectClass
  Geometry: 20x20+0+0
  Units: Undefined
  Type: Palette
  Endianess: Undefined
  Colorspace: sRGB
  Depth: 16-bit
  Channel depth:
    red: 16-bit
    green: 1-bit
    blue: 16-bit
  Channel statistics:
    Pixels: 400
    Red:
      min: 0 (0)
      max: 2495 (0.0380713)
      mean: 1247.65 (0.0190379)                  <--- not very red
      standard deviation: 757.295 (0.0115556)
      kurtosis: -1.20609
      skewness: -0.000125086
      entropy: 1
    Green:
      min: 0 (0)
      max: 0 (0)
      mean: 0 (0)
      standard deviation: 0 (0)
      kurtosis: 0
      skewness: 0
      entropy: nan
    Blue:
      min: 63040 (0.961929)
      max: 65535 (1)
      mean: 64287.3 (0.980962)                     <--- very blue
      standard deviation: 757.295 (0.0115556)
      kurtosis: -1.20609
      skewness: 0.000125086
      entropy: 1

Extract part of an image to identify

1 Answers1