pam-diff

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Measure differences between pixel arrays extracted from pam images. Works well with node module pipe2pam to extract pam images from an ffmpeg pipe. Supported tupltypes are rgb, rgb_alpha, and grayscale. It is currently being used for a video motion detection project.

Installation:

npm install pam-diff --save

Changelog:

version 1.1.0: Percent is now a float to allow for more precise results. Sync option is removed.

Usage Options:

When comparing 2 equally sized buffers of grayscale, rgb, or rgba pixels, there are several options:

• all (default)

  • All pixels will be targeted when checking for differences.
  • To use this option, set the configuration object without creating any regions.

  const pamDiff = new PamDiff({ difference: 5, percent: 5 });
  

• regions

  • Specific regions of pixels will be targeted when checking for differences and the rest will be ignored.
  • To use this option, create a regions array and pass it to the constructor.

  const region1 = {
    name: 'region1',
    difference: 12,
    percent: 22,
    polygon: [
      { x: 0, y: 0 },
      { x: 0, y: 225 },
      { x: 100, y: 225 },
      { x: 100, y: 0 },
    ],
  };
  const region2 = {
    name: 'region2',
    difference: 14,
    percent: 10,
    polygon: [
      { x: 100, y: 0 },
      { x: 100, y: 225 },
      { x: 200, y: 225 },
      { x: 200, y: 0 },
    ],
  };
  const regions = [region1, region2];
  const pamDiff = new PamDiff({ regions: regions });
  

• mask

  • Specific regions of pixels will be ignored when checking for differences.
  • To use this option, create a regions array and set the mask option to true.
  • difference and percent of the individual region is ignored. Set a global value.

  const region1 = {
    name: 'region1',
    polygon: [
      { x: 0, y: 0 },
      { x: 0, y: 225 },
      { x: 100, y: 225 },
      { x: 100, y: 0 },
    ],
  };
  const region2 = {
    name: 'region2',
    polygon: [
      { x: 100, y: 0 },
      { x: 100, y: 225 },
      { x: 200, y: 225 },
      { x: 200, y: 0 },
    ],
  };
  const regions = [region1, region2];
  const pamDiff = new PamDiff({ difference: 12, percent: 10, mask: true, regions: regions });
  

Getting results back from the pixel difference detection:

1. event

   • A diff event will be emitted with a data object passed as the only argument.

   pamDiff.on('diff', data => {
     console.log(data);
   });
   

2. callback

   • A callback function will be called with a data object passed as the only argument.
   • The callback can be passed as the 2nd argument to the constructor, or it can be added later.

   /* callback function */
   function myCallback(data) {
     console.log(data);
   }
   
   /* via the constructor */
   const pamDiff = new pamDiff({ difference: 10, percent: 20 }, myCallback);
   
   /* via the setter */
   pamDiff.callback = myCallback;
   
   /* via the chain-able setter */
   pamDiff.setCallback(myCallback).setDifference(10).setPercent(20);
   
   /* remove the callback */
   pamDiff.callback = null;
   

Expected results:

1. When targeting all pixels:

   {
       trigger: [
           { name: 'all', percent: 13 }
       ],
       pam: <Buffer>,
       headers: <Buffer>,
       pixels: <Buffer>
   }
   

2. When targeting regions of pixels:

   {
       trigger: [
           { name: 'region1', percent: 13 },
           { name: 'region2', percent: 22 }
       ],
       pam: <Buffer>,
       headers: <Buffer>,
      pixels: <Buffer>
   }
   

3. When targeting all pixels ignored by mask:

   {
       trigger: [
           { name: 'mask', percent: 13 }
       ],
       pam: <Buffer>,
       headers: <Buffer>,
       pixels: <Buffer>
   }
   

4. When targeting all pixels and setting {response: "bounds"}:

   {
       trigger: [
           { name: 'all', percent: 13, minX: 42, maxX: 399, minY: 113, maxY: 198 }
       ],
       pam: <Buffer>,
       headers: <Buffer>,
       pixels: <Buffer>
   }
   

5. When targeting all pixels and setting {response: "blobs"}:

   {
       trigger: [
           {
               name: "all",
               percent: 9,
               minX: 137,
               maxX: 1782,
               minY: 392,
               maxY: 695,
               blobs: [
                   {
                       label: 0,
                       percent: 3,
                       minX: 1192,
                       maxX: 1486,
                       minY: 392,
                       maxY: 695
                   },
                   {
                       label: 1,
                       percent: 3,
                       minX: 1488,
                       maxX: 1782,
                       minY: 392,
                       maxY: 695
                   }
               ]
           }
       ],
       pam: <Buffer>,
       headers: <Buffer>,
       pixels: <Buffer>
   }
   

Other Resources:

View the docs, tests, or examples for more implementations.