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pam-diff

Measure differences between pixel arrays extracted from pam images

  • 0.13.10
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pam-diff

dependencies Status Build Status Build status GitHub issues GitHub license npm

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: Async made default in 0.13.6. 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.
New Feature: Starting with version 0.13.5, the option to get the pixel buffer containing the drawn x y bounding box can be set by passing {draw: true} to the pam-diff constructor.
New Feature: Starting with version 0.13.6, the option to filter results by connected component labelling can be set by passing {response: "blobs"} to the pam-diff constructor.
New Feature: Starting with version 0.13.6, async behavior will now be default. If you need the pixel difference measurements to block the event loop, use {sync: true}.

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});
  1. 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});
  1. 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);
}); 
  1. 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>
}
  1. When targeting regions of pixels:
{
    trigger: [
        {name: 'region1', percent: 13},
        {name: 'region2', percent: 22}
    ],
    pam: <Buffer>,
    headers: <Buffer>,
    pixels: <Buffer>
}
  1. When targeting all pixels ignored by mask:
{
    trigger: [
        {name: 'mask', percent: 13}
    ],
    pam: <Buffer>,
    headers: <Buffer>,
    pixels: <Buffer>
}
  1. 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>
}
  1. 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.

Future Plans:

  • Make pre-built binaries available when using node-gyp is not an option.
  • Include option to return coordinates for bounding box of changed pixels.
  • Include option to return pixel buffer containing bounding boxes.
  • Introduce blob filtering to group changed pixels with their neighbors.
  • Include option to return pixel buffer containing bounding boxes around blobs.
  • Make async worker threads the default. Can be overridden with {sync: true}.

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Package last updated on 21 Apr 2019

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