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samwichse
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Joined: 29 Aug 2025
Posts: 107
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 Posted: Fri Jun 16, 2025 1:59 am Post subject: ImageMagick analysis |
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Hey all, any imagemagick gurus out there?
I'm trying to use imagemagick to figure out the percent cover of vegetation from some photographs.
What I'd like to do is set any pixel with a green tinge to be black (basically RGB values where G>R and B) and other values to white, then count the number of both and get a percentage.
Unfortunately, it seems you need to know some C (I don't) and create a custom filter. My posting on the ImageMagick forum got this response:
http://redux.imagemagick.org/discussion-server/viewtopic.html?t=6775
The crux is, I need to change that code, then get it somehow compiled (can you compile just that file... seems like you have to recompile/reinstall the whole package?) to make it do what I want, but I don't even know where to begin.
Seems like it should be easy, but looking at the code to just get the average values gives me a headache.
Sam
Note: I'm trying to do this with free software in a scriptable way... if it works, I'll have hundreds of photos to do.
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samwichse
Member
Joined: 29 Aug 2025
Posts: 107
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| Posted: Sat Jul 01, 2025 3:56 am Post subject: |
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Well, the friend of a friend gave me a hand (thanks Bill)
C code to do this:
| Code: |
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
//ImageMagick Header used in version 6.2.5
#include "magick/ImageMagick.h"
int main( int argc, char **argv)
{
//ExceptionInfo *exception;
ExceptionInfo exception;
Image *image;
ImageInfo *image_info;
const PixelPacket *p;
long x, y;
long greenPix;
long total_pixels;
double percentGreen;
if (argc != 2)
{
fprintf(stdout,"Usage: %s image\n",argv[0]);
exit(0);
}
/*
Initialize the image info structure and read an image.
*/
InitializeMagick( argv[0] );
// Fix
//exception = AcquireExceptionInfo();
GetExceptionInfo( &exception );
image_info = CloneImageInfo( (ImageInfo *) NULL );
strcpy(image_info->filename, argv[1]);
image = ReadImage( image_info, &exception );
if (exception.severity != UndefinedException)
{
CatchException( &exception );
}
if (image == (Image *) NULL)
{
fprintf(stderr,"Failed to Load Image\n");
exit(1);
}
// Do real work...
greenPix = 0;
total_pixels = 0;
// For each row
for ( y = 0; y < (long)image->rows; y++ )
{
p = AcquireImagePixels( image, 0, y, image->columns, 1, &exception );
if (p == (const PixelPacket *) NULL)
{
break;
}
// For each pixel in the row
for( x = 0; x < (long)image->columns; x++ )
{
// check that green is bigger than both red and blue
if ( ( p->green > p->red ) && ( p->green > p->blue ) )
{
greenPix ++;
}
total_pixels++;
p++;
}
}
percentGreen = (double)greenPix / (double)total_pixels * 100;
printf("%s Green Content = %f%%\n", image_info->filename, percentGreen);
// Cleanup...
DestroyImage( image );
image_info = DestroyImageInfo( image_info );
//Fix -- ignore void return type
DestroyExceptionInfo( &exception );
//exception = DestroyExceptionInfo( exception );
DestroyMagick();
return(0);
}
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Germ
Keeper of the BIG STICK
Joined: 30 Apr 2025
Posts: 12452
Location: Planet Earth
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| Posted: Sat Jul 01, 2025 10:07 am Post subject: |
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| Glad you found a solution. I didn't have a clue...
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VHockey86
Advanced Member
Joined: 12 Dec 2025
Posts: 988
Location: Rochester
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| Posted: Sat Jul 01, 2025 11:53 pm Post subject: |
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| Lots of languages have interfaces to the imageMagick API...so you don't neccesarily have to use C
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crouse
Site Admin
Joined: 17 Apr 2025
Posts: 11833
Location: Iowa
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| Posted: Sun Jul 02, 2025 1:53 pm Post subject: |
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I don't know if this could have been done in bash or not..... i've used image magick alot using bash, but i think that the c interfaces are much better documented, however...... having not enough experience with c, i knew i wasn't going to be much help.....
Glad you have a solution, and thank you very much for sharing it ! That's always appreciated.
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VHockey86
Advanced Member
Joined: 12 Dec 2025
Posts: 988
Location: Rochester
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| Posted: Sun Jul 02, 2025 5:56 pm Post subject: |
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| I believe that there are a number of functions that can be achieved through the API, that are not directly accessible with the command line utilities. Thus BASH wouldn't work. For what hes trying to accomplish, it may very well be possible though.
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