如何解决 java opencv memory 不足错误？

Question

import org.opencv.core.Core;
import org.opencv.core.Mat;
import org.opencv.imgcodecs.Imgcodecs;
import java.util.Arrays;

public class Main {

private static double getRGB(int i, int j) {
    Imgcodecs imageCodecs = new Imgcodecs();
    Mat matrix = imageCodecs.imread("/Users/brand/Downloads/SPACE.JPG");
    double rgbVal;
    double rgb[] = matrix.get(i, j);
    rgbVal = rgb[0] + rgb[1] + rgb[2];
    rgbVal = rgbVal / 3;

    return rgbVal;
}
public static void main(String[] args) {
    System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
    Imgcodecs imageCodecs = new Imgcodecs();
    Mat matrix = imageCodecs.imread("/Users/brand/Downloads/SPACE.JPG");
    System.out.println("Image loaded");
    System.out.println("Image size : " + matrix.width() + " x " + matrix.height());
    double[][] rgb = new double[matrix.width()][matrix.height()];

    for (int i = 0; i < matrix.width(); i++) {
        for (int j = 0; j < matrix.height(); j++) {
            rgb[i][j] = getRGB(i, j);
        }
    }
    System.out.println(Arrays.deepToString(rgb));
}
}

When I run my program it takes a very long time to finish, and at the end returns this error:

"Exception in thread "main" CvException [org.opencv.core.CvException: cv::Exception: OpenCV(4.5.0) C:\build\master_winpack-bindings-win64-vc14-static\opencv\modules\core\src\alloc.cpp:73: error: (-4:Insufficient memory) Failed to allocate 921600 bytes in function 'cv::OutOfMemoryError' ]"

The goal of the code is to retrieve the rgb values of each pixel, add them together, and then divide them by 3 in order to get the average value at each pixel. How can I avoid this error that I am receiving. I appreciate any help.

Answer 1

The reason is because at each call to getRGB you load the image again... It allocates those 921600 bytes (maybe 640x480x3) again and again for each pixel in the loop in main. You have to send the image to the function as a parameter, a reference to the Mat, created in main, not to load the image each time.

Apparently these instances created in getRGB are not released and the memory load grows until you run out of system memory. (Watch it using Task Manager, htop etc. depending on your OS)

Not the main problem, but using double is an overkill, the values would be <=255, integer division and bytes would also suffice IMO.