根据另一个 Mat 的非零像素选择 cv::Mat 的一部分？

Question

I am trying to update part of a Mat based on another Mat. For example, I want to select a part of img that is not zero in mask and add a constant value to it. When I try this:

Mat mask = imread("some grayscale image with a white area in a black background", IMREAD_GRAYSCALE);
Mat img = Mat::zeros(mask.rows, mask.cols, CV_8UC1);
Mat bnry, locations;
threshold(mask, bnry, 100, 255, THRESH_BINARY);
findNonZero(bnry, locations);
img(locations) += 5;

I get this error:

Error: Assertion failed ((int)ranges.size() == d)

img and mask have the same size.

How can I select an area of an image based on another image (mask)?

Answer 1

Many of the OpenCV functions will support mask in default, in other word you don't need to find non zero values and based on that doing sum operation, you just need to use cv::add function that in default support using mask as an argument,

cv::add(img,10,img,mask);  // 10 is an arbitrary constant value

And about your code

img(locations) += 5;

As far as I know we don't have any like this overloaded operator+ in OpenCV to use.