Apply Mask to image in OpenCV?

问题

I have a binary mask that I want to be permanently applied to a colour image how would I do this? The binary mask should be preferably permanent- as in I don't want to reapply the mask to the image every time I call a function.

Basic Code Examples would be appreciated. If you use code, please explain the code instead of just posting it.

Thank You

回答1:

You don't apply a binary mask to an image. You (optionally) use a binary mask in a processing function call to tell the function which pixels of the image you want to process. If I'm completely misinterpreting your question, you should add more detail to clarify.

回答2:

While @perrejba s answer is correct, it uses the legacy C-style functions. As the question is tagged C++, you may want to use a method instead:

inputMat.copyTo(outputMat, maskMat);

All objects are of type cv::Mat.

Please be aware that the masking is binary. Any non-zero value in the mask is interpreted as 'do copy'. Even if the mask is a greyscale image.

Also be aware that the .copyTo() function does not clear the output before copying.

If you want to permanently alter the original Image, you have to do an additional copy/clone/assignment. The copyTo() function is not defined for overlapping input/output images. So you can't use the same image as both input and output.

回答3:

You can use the mask to copy only the region of interest of an original image to a destination one:

cvCopy(origImage,destImage,mask);

where mask should be an 8-bit single channel array.

See more at the OpenCV docs

回答4:

Well, this question appears on top of search results, so I believe we need code example here. Here's the Python code:

import cv2

def apply_mask(frame, mask):
    """Apply binary mask to frame, return masked image.
    """
    return cv2.bitwise_and(frame, frame, mask=mask)

Mask and frame must be the same size, so pixels remain as-is where mask is 1 and are set to zero where mask pixel is 0.

And for C++ it's a little bit different:

cv::Mat inFrame; // Original (non-empty) image
cv::Mat mask; // Original (non-empty) mask

// ...

cv::Mat outFrame;  // Result output
inFrame.copyTo(outFrame, mask);

回答5:

Here is some code to apply binary mask on a video frame sequence acquired from a webcam. comment and uncomment the "bitwise_not(Mon_mask,Mon_mask);"line and see the effect.

bests, Ahmed.

#include "cv.h"      // include it to used Main OpenCV functions.
#include "highgui.h" //include it to use GUI functions.

using namespace cv;
using namespace std;

int main(int argc, char** argv)
{
    int c;

int radius=100;
      CvPoint2D32f center;
    //IplImage* color_img;
      Mat image, image0,image1; 
        IplImage *tmp;
    CvCapture* cv_cap = cvCaptureFromCAM(0);

    while(1)  {
        tmp = cvQueryFrame(cv_cap); // get frame
          // IplImage to Mat
            Mat imgMat(tmp);
            image =tmp; 



    center.x = tmp->width/2;
    center.y = tmp->height/2;

         Mat Mon_mask(image.size(), CV_8UC1, Scalar(0,0,0));


        circle(Mon_mask, center, radius, Scalar(255,255,255), -1, 8, 0 ); //-1 means filled

        bitwise_not(Mon_mask,Mon_mask);// commenté ou pas = RP ou DMLA 





        if(tmp != 0)

           imshow("Glaucom", image); // show frame

     c = cvWaitKey(10); // wait 10 ms or for key stroke
    if(c == 27)
        break; // if ESC, break and quit
    }
    /* clean up */
    cvReleaseCapture( &cv_cap );
    cvDestroyWindow("Glaucom");

}

回答6:

Explanation with example

import cv2
import numpy as np

img1 = cv2.imread("road.jpg")
img2 = cv2.imread("car.jpg")
img2_gray = cv2.cvtColor(img2, cv2.COLOR_BGR2GRAY)
ret, mask = cv2.threshold(img2_gray, 240, 255, cv2.THRESH_BINARY)
mask_inv = cv2.bitwise_not(mask)
road = cv2.bitwise_and(img1, img1, mask=mask)
car = cv2.bitwise_and(img2, img2, mask=mask_inv)
result = cv2.add(road, car)
cv2.imshow("img1", img1)
cv2.imshow("img2", img2)
cv2.imshow("road background", road)
cv2.imshow("car no background", car)
cv2.imshow("mask", mask)
cv2.imshow("mask inverse", mask_inv)
cv2.imshow("result", result)
cv2.waitKey(0)
cv.destroyAllWindows()

来源：https://stackoverflow.com/questions/7479265/apply-mask-to-image-in-opencv

标签

c++

image

image-processing

OpenCV

mask