How to draw contour for a document in OpenCV.js?

asked 2020-11-21 04:35:54 -0500

kani gravatar image

Greetings! I'm a beginner with OpenCV, I stumbled with a problem to draw 4 point contours around document image, I followed a tutorial from pyimagesearch for Python and i want to implement this example in Opencv.js I found an example for JavaScript from StackOverflow but getting the following error:

BindingError {name: "BindingError", message: "Cannot pass "[object Object]" as a MatVector", 
stack: "BindingError: Cannot pass "[object Object]....

I understand the meaning of an error i'm getting but not sure what exactly should i pass to drawContours method

Here is my example:

let color = new cv.Scalar(0, 255, 0);
  let edgeDetected = new cv.Mat();
  let contours = new cv.MatVector();
  let hierarchy = new cv.Mat();
  cv.Canny(img, edgeDetected, 100, 200, 3, true);
  cv.findContours(edgeDetected, contours, hierarchy, cv.RETR_EXTERNAL, cv.CHAIN_APPROX_NONE);

  let foundContour = new cv.MatVector();

  //Get area for all contours so we can find the biggest
  let sortableContours = [];
  for (let i = 0; i < contours.size(); i++) {
    let cnt = contours.get(i);
    let area = cv.contourArea(cnt, false);
    let perim = cv.arcLength(cnt, false);

    sortableContours.push({ areaSize: area, perimiterSize: perim, contour: cnt });
  }

  sortableContours = sortableContours.sort((item1, item2) => { return (item1.areaSize > item2.areaSize) ? -1 : (item1.areaSize < item2.areaSize) ? 1 : 0; }).slice(0, 5);

  //Ensure the top area contour has 4 corners (NOTE: This is not a perfect science and likely needs more attention)
  let approx = new cv.Mat();
  cv.approxPolyDP(sortableContours[0].contour, approx, .05 * sortableContours[0].perimiterSize, true);

  if (approx.rows == 4) {
    console.log('Found a 4-corner approx');
    foundContour = approx;
  }
  else{
    console.log('No 4-corner large contour!');
    return;
  }

  //Find the corners
  let corner1 = new cv.Point(foundContour.data32S[0], foundContour.data32S[1]);
  let corner2 = new cv.Point(foundContour.data32S[2], foundContour.data32S[3]);
  let corner3 = new cv.Point(foundContour.data32S[4], foundContour.data32S[5]);
  let corner4 = new cv.Point(foundContour.data32S[6], foundContour.data32S[7]);

  //Order the corners
  let cornerArray = new cv.MatVector();
  cornerArray = [{ corner: corner1 }, { corner: corner2 }, { corner: corner3 }, { corner: corner4 }];
  //Sort by Y position (to get top-down)
  cornerArray.sort((item1, item2) => { 
    return (item1.corner.y < item2.corner.y) ? -1 : (item1.corner.y > item2.corner.y) ? 1 : 0; 
  }).slice(0, 5);

  for (c of cornerArray) {
    cv.drawContours(img, c.corner, -1, color, 1, cv.LINE_8, hierarchy, 100);
  }

  cv.imshow('canvasOutput', img);
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Comments

Comment out let cornerArray = new cv.MatVector();:

//Order the corners
let cornerArray = [{ corner: corner1 }, { corner: corner2 }, { corner: corner3 }, { corner: corner4 }];
supra56 gravatar imagesupra56 ( 2020-11-21 21:19:07 -0500 )edit
1

I still have the same Binding error

BindingErrorĀ {name: "BindingError", message: "Cannot pass "[object Object]" as a MatVector"
kani gravatar imagekani ( 2020-11-22 08:48:51 -0500 )edit

Comment out this one let foundContour = new cv.MatVector(); And see what happened.

supra56 gravatar imagesupra56 ( 2020-11-22 21:08:09 -0500 )edit
1

I already did that and I got the same BInding error

kani gravatar imagekani ( 2020-11-23 02:48:47 -0500 )edit

Sadly. My friend can't help u.

supra56 gravatar imagesupra56 ( 2020-11-23 03:31:33 -0500 )edit