Revision history [back]

Hi,

I'm trying to implement AKAZE with opencv.js and opencv-wasm.

Here is my code:

const { cv, cvTranslateError } = require('opencv-wasm');
const Jimp = require('jimp');
const util = require('./util.js');

 (async () => {
     try {
         console.log("Enter 1");
         const jimpSrc = await Jimp.read("./images/how_to_play.png");
         const jimpSrcToMatch = await Jimp.read("./images/scene.png");

    console.log("Enter 2");
    // initiate ORB detector, default number of features to retain is 500, bit too low
    let akaze = new cv.AKAZE();
    let img1 = await cv.matFromImageData(jimpSrc.bitmap);
    let img2 = await cv.matFromImageData(jimpSrcToMatch.bitmap);
    let res = new cv.Mat();
    let mask1 = new cv.Mat();
    let mask2 = new cv.Mat();
    console.log("Enter 3");

    cv.cvtColor(img1, img1, cv.COLOR_BGRA2GRAY, 0);
    cv.cvtColor(img2, img2, cv.COLOR_BGRA2GRAY, 0);

    // find descriptors and keypoints with AKAZE detector
    let kp1 = new cv.KeyPointVector();
    let kp2 = new cv.KeyPointVector();
    let des1 = new cv.Mat();
    let des2 = new cv.Mat();

    akaze.detectAndCompute(img1, mask1, kp1, des1);
    akaze.detectAndCompute(img2, mask2, kp2, des2);

    // create BFMatcher object and and match descriptors
    let matcher = new cv.BFMatcher();
    let matches = new cv.DMatchVectorVector();
    let filteredMatches = new cv.DMatchVector();

    matcher.knnMatch(des1, des2, matches, 2);

    // filter matches
    for (let i = 0; i < matches.size(); ++i) {
        let match = matches.get(i);
        let dMatch1 = match.get(0);
        let dMatch2 = match.get(1);
        if (dMatch1.distance <= dMatch2.distance * 0.7) {
            filteredMatches.push_back(dMatch1);
        }
    }

    cv.drawMatches(img1, kp1, img2, kp2, filteredMatches, res);
    util.saveMat(res, "matcher-output.png");

    if (filteredMatches.size() > 13) {
        let objectPoints = [];
        let scenePoints = [];

        for (let i = 0; i < filteredMatches.size(); ++i) {
            let dMatch = filteredMatches.get(i);
            objectPoints.push(
                new cv.Point(kp1.get(dMatch.queryIdx).pt.x, kp1.get(dMatch.queryIdx).pt.y));
            scenePoints.push(
                new cv.Point(kp2.get(dMatch.trainIdx).pt.x, kp2.get(dMatch.trainIdx).pt.y));
        }

        let homography = cv.findHomography(
            cv.matFromArray(objectPoints.length, 3, cv.CV_32F, objectPoints),
            cv.matFromArray(scenePoints.length, 3, cv.CV_32F, scenePoints), cv.RANSAC, 3);
        let sceneCorners = new cv.Mat(4, 1, cv.CV_32FC2);
        //let objCorners = cv.matFromArray(4, 1, cv.CV_32FC2, [0, 0, img1.cols - 1, 0, img1.cols - 1, img1.rows - 1, 0, img1.rows - 1]);
        let objCorners = new cv.Mat(4, 1, cv.CV_32FC2);

        console.log("Transforming object corners to scene corners...");
        // cv.perspectiveTransform(objCorners, sceneCorners, homography);

        var view = objCorners.data32F;
        view[0] = 0;
        view[1] = 0;
        view[2] = img1.cols;
        view[3] = 0;
        view[4] = img1.cols;
        view[5] = img1.rows;
        view[6] = 0;
        view[7] = img1.rows;

        cv.perspectiveTransform(objCorners, sceneCorners, homography);

        var dataAns = sceneCorners.data32F;

        var x1 = new cv.Point(dataAns[0], dataAns[1]);
        var x2 = new cv.Point(dataAns[2], dataAns[3]);
        var x3 = new cv.Point(dataAns[4], dataAns[5]);
        var x4 = new cv.Point(dataAns[6], dataAns[7]);

        cv.line(res, x1, x2,
            new cv.Scalar(0, 0, 0), 10, cv.LINE_AA, 0);
        cv.line(res, x2, x3,
            new cv.Scalar(0, 0, 0), 10, cv.LINE_AA, 0);
        cv.line(res, x3, x4,
            new cv.Scalar(0, 0, 0), 10, cv.LINE_AA, 0);
        cv.line(res, x4, x1,
            new cv.Scalar(0, 0, 0), 10, cv.LINE_AA, 0);
    }

} catch (err) {
    console.log(cvTranslateError(cv, err));
}
})();

The problem is, that final corners coordinates x1, x2, x3, x4 are always like 1.00007678, 0.9999767623, -0.9878787.... Any ideas why?

P.S I'm well familiar with opencv for Java and Python.