CODEWITHSUNDEEP
matlabopencvimage-processingmat
sam ran
sam ran

Reputation: 137

how to modify values of Mat according to some condition in opencv?

In Matlab a(a>50)=0 can replace all elements of a that are greater than 50 to 0. I want to do same thing with Mat in OpenCV. How to do it?

Upvotes: 8

Views: 11341

Answers (3)

Ashutosh Gupta
Ashutosh Gupta

Reputation: 680

Naah. to do that, just one line:

cv::Mat img = imread('your image path');
img.setTo(0,img>50);

as simple as that.

Upvotes: 28

Dinidiniz
Dinidiniz

Reputation: 811

Sometimes threshold doesn't work because you can have a diferent kind of Mat. If your Mat type supports double, threshold will crash (at least in my android studio).

You can find compare here: http://docs.opencv.org/2.4/modules/core/doc/operations_on_arrays.html

So I use the function compare:

Mat mask = new Mat(yourMat.rows(), yourMat.cols(), CvType.CV_64FC1);
Mat ones = org.opencv.core.Mat.ones(yourMat.rows(), yourMat.cols(), CvType.CV_64FC1);
Scalar alpha = new Scalar(50, CvType.CV_64FC1);
Core.multiply(ones, alpha, ones);

Core.compare(yourMat, zeros, mask, Core.CMP_LT);

Here I am creating a matrix with only 50 in all points. After that i am comparing it with yourMat, using CMP_LT (Less than). So all pixels less than 50 will turn in 255 in your mask and 0 if bigger. It is a mask. So you can just:

yourMat.copyTo(yourMat, mask);

Now all the pixels bigger than 50 will be zero and all the other will have their own values.

Upvotes: 0

Gilad
Gilad

Reputation: 6575

What you want is to truncate the image with cv::threshold.

The following should do what you require:

cv::threshold(dst, dst, 50, 0, CV_THRESH_TOZERO_INV);

this is the function definition

double threshold(InputArray src, OutputArray dst, double thresh, double maxval, int type)

http://docs.opencv.org/modules/imgproc/doc/miscellaneous_transformations.html?highlight=threshold#threshold

Upvotes: 10

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