Apply Gamma Correction to an Image using OpenCV

Images can look either too light or too dark. Gamma correction is a method that allows to control the brightness of an image. The formula used to get a gamma corrected image is given below:

• I - input pixel value [0, 255].
• O - output pixel value [0, 255].
• γ - gamma that controls image brightness. If gamma < 1 then the image will be darker, if gamma > 1 then the image will be lighter. A gamma = 1 has no effect.

An image pixel values are converted from the range [0, 255] to [0, 1.0]. After calculations, values are converted back to the range [0, 255].

Gamma correction can be implemented using lookup table (LUT). It maps the input pixel values to the output values. For each pixel value in the range [0, 255] is calculated a corresponding gamma corrected value. OpenCV provides the LUT function which performs a lookup table transform.

import cv2
import numpy as np


def gammaCorrection(src, gamma):
    invGamma = 1 / gamma

    table = [((i / 255) ** invGamma) * 255 for i in range(256)]
    table = np.array(table, np.uint8)

    return cv2.LUT(src, table)


img = cv2.imread('test.jpg')
gammaImg = gammaCorrection(img, 2.2)

cv2.imshow('Original image', img)
cv2.imshow('Gamma corrected image', gammaImg)
cv2.waitKey(0)
cv2.destroyAllWindows()

#include <opencv2/opencv.hpp>

using namespace cv;

void gammaCorrection(const Mat &src, Mat &dst, const float gamma)
{
    float invGamma = 1 / gamma;

    Mat table(1, 256, CV_8U);
    uchar *p = table.ptr();
    for (int i = 0; i < 256; ++i) {
        p[i] = (uchar) (pow(i / 255.0, invGamma) * 255);
    }

    LUT(src, table, dst);
}

int main()
{
    Mat img = imread("test.jpg");
    Mat gammaImg;
    gammaCorrection(img, gammaImg, 2.2);

    imshow("Original image", img);
    imshow("Gamma corrected image", gammaImg);
    waitKey(0);
    destroyAllWindows();

    return 0;
}

package app;

import org.opencv.core.Core;
import org.opencv.core.CvType;
import org.opencv.core.Mat;
import org.opencv.highgui.HighGui;
import org.opencv.imgcodecs.Imgcodecs;

public class Main
{
    static { System.loadLibrary(Core.NATIVE_LIBRARY_NAME); }

    public static void gammaCorrection(Mat src, Mat dst, float gamma)
    {
        float invGamma = 1 / gamma;

        Mat table = new Mat(1, 256, CvType.CV_8U);
        for (int i = 0; i < 256; ++i) {
            table.put(0, i, (int) (Math.pow(i / 255.0f, invGamma) * 255));
        }

        Core.LUT(src, table, dst);
    }

    public static void main(String[] args)
    {
        Mat img = Imgcodecs.imread("test.jpg");
        Mat gammaImg = new Mat();
        gammaCorrection(img, gammaImg, 2.2f);

        HighGui.imshow("Original image", img);
        HighGui.imshow("Gamma corrected image", gammaImg);
        HighGui.waitKey(0);
        HighGui.destroyAllWindows();

        System.exit(0);
    }
}

Result: