voluptasquisquam/src/image/compute/__tests__/histogram.js

Image processing and manipulation in JavaScript

import {Image} from 'test/common';
import 'should';

describe('calculate the histogram', function () {
    it('check getHistogram method', function () {

        let image = new Image(1, 2, [230, 83, 120, 255, 100, 140, 13, 1]);

        let histogram = image.getHistogram({useAlpha: false, channel: 0});
        histogram[0].should.equal(0);
        histogram[100].should.equal(1);
        histogram[230].should.equal(1);
        histogram[255].should.equal(0);

        histogram = image.getHistogram({useAlpha: false, channel: 2});
        histogram[0].should.equal(0);
        histogram[13].should.equal(1);
        histogram[120].should.equal(1);
        histogram[255].should.equal(0);
    });


    it('check histogram property', function () {

        let image = new Image(1, 4, [230, 255, 230, 255, 230, 255, 13, 1], {
            kind: 'GREYA'
        });

        let histogram = image.histogram;

        histogram[0].should.equal(0);
        histogram[1].should.equal(0);
        histogram[13].should.approximately(0.0039, 0.0001);
        histogram[100].should.equal(0);
        histogram[230].should.equal(3);
        histogram[255].should.equal(0);
    });

    it('check 16 slots histogram', function () {

        let image = new Image(1, 4, [230, 255, 230, 255, 230, 255, 13, 1], {
            kind: 'GREYA'
        });

        let histogram = image.getHistogram({maxSlots: 16});

        histogram[0].should.approximately(0.0039, 0.0001);
        histogram[1].should.equal(0);
        histogram[14].should.equal(3);
        histogram[15].should.equal(0);
    });

    it('check histogram for 1 bit image', function () {
        let image = new Image(5, 5,
            [
                0, 0, 0, 0, 0,
                0, 255, 255, 255, 0,
                0, 255, 255, 255, 0,
                0, 255, 255, 255, 0,
                0, 0, 0, 0, 0
            ],
            {kind: 'GREY'}
        );
        let image2 = image.mask();
        let histogram = image2.getHistogram();
        histogram[0].should.eql(16);
        histogram[1].should.eql(9);

    });
});