Opencv4nodejs: Help with bitwiseAnd method

[mgs96]

Hello, I'm having trouble with getting colors from an image, I get the mask but I can't filter separate the colours, here is my code:

const cv = require('opencv4nodejs');

let img = cv.imread('./cart.jpg');

let boundaries = [
    {
        lower: [17, 15, 100],
        upper: [50, 56, 200]
    },
    {
        lower: [86, 31, 4],
        upper: [220, 88, 50]
    },
    {
        lower: [25, 146, 190],
        upper: [62, 174, 250]
    },
    {
        lower: [103, 86, 65],
        upper: [145, 133, 128]
    }
]

for (const boundary of boundaries) {
    let lower = new cv.Vec3(...boundary.lower);
    let upper = new cv.Vec3(...boundary.upper);
    let mask = img.inRange(lower, upper);
    let output = img.bitwiseAnd(mask);
    cv.imwrite('source' + Date.now() + '.jpg', output);
}

the error I'm getting is libc++abi.dylib: terminating with uncaught exception of type std::runtime_error Abort trap: 6 produced by this line let output = img.bitwiseAnd(mask);, I've already tried changing the order of the params like this mask.bitwiseAnd(img); but I get the same error.

I'm running it under node v8.12.0 and opencv4nodejs ^4.11.0. Thanks in advance

[andrewwalters]

Those are usually failed assertions in the OpenCV library itself, often because of invalid arguments. In this case, it might be because you're trying to bitwise AND a 3-channel and 1-channel image together.

You could AND each channel with your mask independently and then join them:

let channels = img.splitChannels();
let maskedChannels = channels.map(c => c.bitwiseAnd(mask));
let output = new cv.Mat(maskedChannels);

[mgs96]

thank you @andrewwalters, it works!