Feature request: global tolerance value

[cburgmer]

I have a use case where I'd like to compare images using a global tolerance aka "the images are less than 5% different". So far equal only accounts for a threshold on a per color and pixel value.

The implementation is probably fairly trivial, I'd see the difficulty in finding a meaningful way of integrating that.

Would that feature make sense here?

[cesutherland]

I think it would make sense. To do so, I'd like to see toImageDiffEqual(expected, tolerance) implemented as toImageDiffEqual(expected, options).

With an options configuration like:

{
  tolerance : 0.05,
  globalTolerance : true
}

Or something along those lines.

[cburgmer]

Would you then also change the unit of tolerance for the per-pixel basis? Right now it is measured in pixels.

[janouma]

Here is how I see it:

...

function equal(a, b, tolerance, errorPercentageAllowed) {

    var
        aData = a.data,
        bData = b.data,
        length = aData.length,
        i,
        mismatchesCount = 0,
        errorPercentage;

    tolerance = tolerance || 0;
    errorPercentageAllowed = errorPercentageAllowed || 0;

    if (!equalDimensions(a, b)) return false;

    for (i = length; i--;) {
        if (aData[i] !== bData[i] && Math.abs(aData[i] - bData[i]) > tolerance) {
            mismatchesCount++;
        }
    }

    errorPercentage = (mismatchesCount / length) * 100;

    if (errorPercentage > errorPercentageAllowed) {
        console.log('mismatchesCount: ' + mismatchesCount);
        console.log('length: ' + length);
        console.log(errorPercentage + ' % mismatches encountered');
        return false;
    } else {
        return true;
    }
}

...