使用OpenCV.js进行投影变换后结果为空白透明图片的原因是什么？如何解决？

// 投影变换
let srcQuad = cv.matFromArray(4, 1, cv.CV_32FC2, points.flat());
let dstQuad = cv.matFromArray(4, 1, cv.CV_32FC2, [0, 0, img.cols, 0, img.cols, img.rows, 0, img.rows]);
let transmtx = cv.getPerspectiveTransform(srcQuad, dstQuad);
let target = new cv.Mat();
cv.warpPerspective(img, target, transmtx, new cv.Size(img.cols, img.rows));
// 显示结果
cv.imshow(canvas, target);

imgElement.onload = function() {
    try {
        img = cv.imread(imgElement);
        if (img.empty()) {
            console.error("图像加载失败！");
            return;
        }

        // 设置Canvas尺寸
        let canvas = document.getElementById('canvasOutput');
        canvas.width = img.cols;
        canvas.height = img.rows;

        // ... (投影变换代码，与原代码相同) ...

        cv.imshow(canvas, target);

        // 释放Mat对象
        img.delete();
        srcQuad.delete();
        dstQuad.delete();
        transmtx.delete();
        target.delete();

    } catch (error) {
        console.error("发生错误:", error);
    }
};

imgElement.onerror = function() {
    console.error("图像加载失败！");
};