Threshold Plugin

[brownrw8]

Add "threshold" method to image. I believe this is useful as a simplified method for processing scanned drawings, signatures, etc. I've used a couple other methods for this but I always end up having to chain multiple calls/set up variables to get the same effect.

var {Jimp, getTestDir} = require("./test-helper");

describe("Threshold", function () {

    this.timeout(15000);

    var originalRenditionPath = getTestDir() + "/samples/hands.jpg";
    var lighterRenditionPath = getTestDir() + "/samples/threshold-samples/hands_mx200_rp255.jpg";

    var originalRendition, lighterRendition;
    before((done)=> {
        var imgs = [];
        imgs.push(Jimp.read(originalRenditionPath));
        imgs.push(Jimp.read(lighterRenditionPath));
        Promise.all(imgs).then((loadedImgs)=> {
            originalRendition = loadedImgs[0];
            lighterRendition = loadedImgs[1];
            done();
        }).catch(done);
    });

    it("defines default threshold for lighter backgrounds", ()=> {
        var transformedOriginalRendition = originalRendition.threshold(200, 255);
        transformedOriginalRendition.hash().should.be.equal(lighterRendition.hash());
    });

});

[edi9999]

Looks good to me.

The only thing I don't like that much is the autoGrayscale

I find it better to let the users be more explicit.

The fact that the API is chainable makes things easy too :

image.grayScale(...).threshold(...)

So I suggest to remove the autoGrayscale parameter.

[hipstersmoothie]

@edi9999 I have updated this PR and added threshold as a plugin. I think keeping the autogreyscale is fine since it helps get better output from scan.

[edi9999]

Ok, fine