How to normalize image in openCV?

Question

I am totally new in openCV and stuck at one point.

I have a grey scale image but I need to normalize this image. For example: I have a cv::mat image which may have a matrix containing some values and each index. As I have gray image it may contain only 1 value per index. Now I need to divide each value by 255.

Is there any method or facility available in openCV in C++? For this scenario, I believe the method I want to use is called normalization in openCV?

cv::Mat originalMat = [OSInference cvMatFromUIImage:imgBeforeProccessing];
cv::Mat img2;

cv::cvtColor(originalMat, img2,CV_BGR2GRAY);
cv::resize(img2, img2, cv::Size(128, 128), 0, 0, CV_INTER_CUBIC);
cv::Mat img3;

Now how to normalise (this means to divide each value in the matrix by 255)??

I am converting the mat image to an iOS image as follows:

+ (UIImage *)UIImageFromCVMat:(cv::Mat)cvMat{
    NSData *data = [NSData dataWithBytes:cvMat.data length:cvMat.elemSize()*cvMat.total()];

    CGColorSpaceRef colorspace;

    if (cvMat.elemSize() == 1) {
        colorspace = CGColorSpaceCreateDeviceGray();
    }else{
        colorspace = CGColorSpaceCreateDeviceRGB();
    }

    CGDataProviderRef provider = CGDataProviderCreateWithCFData((__bridge CFDataRef)data);

    // Create CGImage from cv::Mat
    CGImageRef imageRef = CGImageCreate(cvMat.cols, cvMat.rows, 8, 8 * cvMat.elemSize(), cvMat.step[0], colorspace, kCGImageAlphaNone | kCGBitmapByteOrderDefault, provider, NULL, false, kCGRenderingIntentDefault);

    // get uiimage from cgimage
    UIImage *finalImage = [UIImage imageWithCGImage:imageRef];
    CGImageRelease(imageRef);
    CGDataProviderRelease(provider);
    CGColorSpaceRelease(colorspace);

    return finalImage;
}

Answer 1

To normalize cv::Mat you can use cv::normalize. I write some code to help you.

uchar data[] = {0, 63, 127, 255};
cv::Mat im(2, 2, CV_8UC1, data), output;
# this what you need 0 -> min value after norm
# 1 -> max value after nom
# cv::NORM_MINMAX normalize for min and max values
cv::normalize(im, output, 0, 1, cv::NORM_MINMAX);
std::cout 
    << im     << '\n'
    << output << '\n';
#==================================================
# output
[  0,  63;
   127, 255]
[  0,   0;
   0,   1]

Answer 2

OpenCV has a function does exactly what you want. It's called convertTo.

cv::Mat img3;
img2.convertTo(img3, CV_32F, 1.0 / 255, 0);