Reproduce Gimp Convolution in jimp (Convolution matrix)

[jBernavaPrah]

I can not reproduce the same result I have on Gimp. What I do wrong?

Original Image:

With gimp I use this procedure: Filter-> Generic-> Convolution Matrix.
Settings:

Result:

With jimp "0.2.28" on Node:

original_image = original_image.convolute([
            [0, 0, 0, 0, 0],
            [0, 1, 1, 1, 0],
            [0, 1, 0, 1, 0],
            [0, 1, 1, 1, 0],
            [0, 0, 0, 0, 0],
        ]);

Result:

Thanks!

[andq-ibl]

The problem is that the convolution function in Jimp does not handle the case new pixel value is greater than 255

[steffkelsey]

You can try monkey-patching the convolute function to this:

    if (!Array.isArray(kernel))
        return throwError.call(this, "the kernel must be an array", cb);

    if (typeof x === "function") {
        cb = x;
        x = y = w = h = null;
    } else {
        if (isDef(x) && typeof x !== "number")
            return throwError.call(this, "x must be a number", cb);
        if (isDef(y) && typeof y !== "number")
            return throwError.call(this, "y must be a number", cb);
        if (isDef(w) && typeof w !== "number")
            return throwError.call(this, "w must be a number", cb);
        if (isDef(h) && typeof h !== "number")
            return throwError.call(this, "h must be a number", cb);
    }

    let ksize = (kernel.length - 1) / 2;

    x = isDef(x) ? x : ksize;
    y = isDef(y) ? y : ksize;
    w = isDef(w) ? w : this.bitmap.width - x;
    h = isDef(h) ? h : this.bitmap.height - y;

    var source = this.cloneQuiet();
    this.scanQuiet(x, y, w, h, function (xx, yx, idx) {
        var value = applyKernel(source, kernel, xx, yx);

        this.bitmap.data[idx] = Math.max(0, Math.min(value[0], 255));
        this.bitmap.data[idx + 1] = Math.max(0, Math.min(value[1], 255));
        this.bitmap.data[idx + 2] = Math.max(0, Math.min(value[2], 255));
    });

    if (isNodePattern(cb)) return cb.call(this, null, this);
    else return this;
};```

That would keep all the final values between 0 and 255.

[hipstersmoothie]

@steffkelsey why monkey patch when you can make a PR. please do!

[hipstersmoothie]

Released in v0.4.0