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How can i fill the gaps in the foreground and improve foreground extraction?

asked 2018-02-15 09:30:01 -0500

generator gravatar image

updated 2018-02-15 09:30:16 -0500

I want to improve my foreground extraction on my opencv.js project.I am extracting moving foreground from static background.My output foreground have gaps and little bit noisy. How can i fill this gaps with original foreground object color?





Here is my code:

let video = document.getElementById('videoInput');
let cap = new cv.VideoCapture(video);

let frame = new cv.Mat(video.height, video.width, cv.CV_8UC4);
let fgmask = new cv.Mat(video.height, video.width, cv.CV_8UC1);
let fgbg = new cv.BackgroundSubtractorMOG2(500, 16, false);

const FPS = 30;
function processVideo() {
    try {
        if (!streaming) {
            // clean and stop.
            frame.delete(); fgmask.delete(); fgbg.delete();
        let begin =;
        // start processing.;
        fgbg.apply(frame, fgmask);

        frame.copyTo(fgmask, fgmask)    
        cv.imshow('canvasOutput', fgmask);
        // schedule the next one.
        let delay = 1000/FPS - ( - begin);
        setTimeout(processVideo, delay);
    } catch (err) {

// schedule the first one.
setTimeout(processVideo, 0);
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3 answers

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answered 2018-02-15 10:41:08 -0500

Tetragramm gravatar image

Take a look at this tutorial: Morphological Operations

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Thank you.I am trying to Opening process because it says "It is useful in removing noise." but it doesn't work.

Without opening:

With Opening:

generator gravatar imagegenerator ( 2018-02-15 11:06:49 -0500 )edit

You need to read a bit more carefully. Notice how in the tutorial, Opening is white on a black background. In your case, you have (darker) things on a white background.

Tetragramm gravatar imageTetragramm ( 2018-02-15 11:14:02 -0500 )edit

Then,How can i implement Morphological Operations?Maybe "reversing background color and foreground color" work

generator gravatar imagegenerator ( 2018-02-15 11:39:27 -0500 )edit

Try copying the frame to a black image, using the fgmask.

Tetragramm gravatar imageTetragramm ( 2018-02-15 17:47:20 -0500 )edit

I use bitwise_not for reversing background color and foreground color.And i use opening for removing background noise and closing image for closing small holes inside the foreground objects.But It didn't work Without Closing and Opening :

With Closing and Opening :

Closing and Opening Code :

generator gravatar imagegenerator ( 2018-02-16 03:07:30 -0500 )edit

So, you still aren't really reading what these functions are doing.

Take the code from your link and insert it before the frame.copyTo. Do not do the bitwise_not. That is because if you operate on the fgmask, you already have a white foreground and black background. It's after the copyTo that you get the white background.

Tetragramm gravatar imageTetragramm ( 2018-02-16 15:47:17 -0500 )edit

answered 2018-02-16 05:07:10 -0500

What you should do in my opinion

  • Apply on your binary mask some erosion and dilation until you only have pixels left that are part of the movement
  • Then you put all those points into a vector and calculate the convex hull on all those points
  • Now on top of your mask draw that convexHull with filled option on

This will include all the inner pixels also in your foreground mask!

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answered 2018-02-21 12:04:03 -0500

ManuVISION gravatar image
  1. A morphological open with a small kernel to remove all small speckles

  2. Find the largest closed contour and fit a convex hull around it.

  3. Fill the convex hull with white, while the background is black

  4. Use the binary mask from step 3 and copy the contents of the original image onto an all white image using the binary mask as reference.

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Wait a second, what is different in your approach opposed to mine?

StevenPuttemans gravatar imageStevenPuttemans ( 2018-02-22 03:50:33 -0500 )edit

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Asked: 2018-02-15 09:30:01 -0500

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Last updated: Feb 21 '18