pam-diff

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@latest --save

Important Note: The js-only version will no longer receive any updates. All future work will be dedicated to the n-api version because it is much more efficient.

New Feature: Starting with version 0.13.0, the option to use worker threads can be enabled by passing {async: true} to the pam-diff constructor.

New Feature: Starting with version 0.13.2, the option to get x y bounding box coordinates can be set by passing {response: "bounds"} to the pam-diff constructor.

Usage Options:

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

1. 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});

2. 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});

3. 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.

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>
}

2. When targeting regions of pixels:

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

3. When targeting all pixels ignored by mask:

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

Other Resources:

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

Future Plans:

• Add node-pre-gyp as an option for installing pre-built binaries for those who are unable to use node-gyp. (Not a priority at this point)
• Include option to return coordinates for bounding box of changed pixels.
• Introduce blob filtering to group changed pixels with their neighbors.