[vox-tech] count pixels

[Jeff Newmiller]

Wade Pinkston wrote:
> I put a webpage up with an example.
> 
> http://bugs.osu.edu/wade

JPEG is a poor choice for this since the compression messes with colors
near edges.  If you are stuck with it though, you may want to play with 
ppmquant.

> As you can see its the same image but the first has no damage.  The 
> second has damage.  So what I need it the percent difference.

$ RED5=`jpegtopnm red5.jpg 2>/dev/null | ppmhist \
| egrep '^[ ]*254[ ]+0[ ]+0' \
| perl -ne 'if ( /^\s*[0-9]+\s+[0-9+]+\s+[0-9+]+\s+[0-9+]+\s+([0-9]+)/ ) { 
print $1 };'`

$ RED4=`jpegtopnm red4.jpg 2>/dev/null | ppmhist | \
egrep '^[ ]*254[ ]+0[ ]+0' | \
perl -ne 'if ( /^\s*[0-9]+\s+[0-9+]+\s+[0-9+]+\s+[0-9+]+\s+([0-9]+)/ ) { 
print $1 };'`

$ perl -e "print (100*$RED5)/$RED4-100, \"\\n\";"

> Jim Angstadt wrote:
> 
>> --- Wade Pinkston <blata at bugs.osu.edu> wrote:
>>
>>> -----BEGIN PGP SIGNED MESSAGE-----
>>> Hash: SHA1
>>>
>>> Hello,  I need to process some images and count the
>>> number of pixes of a
>>> given color.
>>>
>>> A little background.  I want to take pix of leaves
>>> against a mat
>>> background.  The leaves are then subjected to
>>> damage.  I'll then take a
>>> duplicate photo.  Now what I want to do is subtract
>>> out the colors of the
>>> leaf leaving only a two tone image.
>>>
>>> I was hoping to find a way to then use ImageMagick
>>> or Gimp to count the
>>> pixels of color so I can then get a percent change
>>> between the two images.
>>>
>>> Does anybody know how to get ether of these two
>>> programs to give this type
>>> of information.  Actually any software would be help
>>> full.
>>
>>
>> Here is an example of using IM to compare 2 images, in
>> this case, images from a webcam:
>>
>>  http://www.notbig.org/bin/webcam.sh.txt
>>
>> Note the command that begins with
>>   differ=$(composite
>> which first compares 2 images, then ignores minor
>> color variations, converts the pixel comparison to
>> text, and then manipulates the text as needed.
>>
>> I don't really understand what you are trying to do,
>> but this sample of IM make be helpful for image
>> comparisons.
>>
>> Jim

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