c++ - OpenCV HDR processing producing bad output on iOS

Question

I am trying to create an HDR image from 7 images taken with different exposure values on iOS. I used the OpenCV cocoapod and followed this GitHub repository to implement HDR processing. I have got the fusion image working and it has a decent picture output, however, the HDR version produces a bad output. It somewhat looks like the image is a negative version of what it should be. See below:

I have tried to mess around with my code to produce 8-bit and 32-bit versions of this image since that's what I read on some other questions.

I also included my HDR.cpp file that does the merging to HDR:

cv::Mat mergeToHDR (vector<Mat>& images, vector<float>& times)
{
    imgs = images;
    Mat response;
    Ptr<CalibrateDebevec> calibrate = createCalibrateDebevec();
    calibrate->process(images, response, times);


    // Ptr<CalibrateRobertson> calibrate = createCalibrateRobertson();
    // calibrate->process(images, response, times);

    // create HDR
    Mat hdr;
    Ptr<MergeDebevec> merge_debevec = createMergeDebevec();
    merge_debevec->process(images, hdr, times, response);

    // create fusion
    // Mat fusion;
    // Ptr<MergeMertens> merge_mertens = createMergeMertens();
    // merge_mertens->process(images, fusion);

    // fusion
    // Mat fusion8bit;
    // fusion = fusion * 255;
    // fusion.convertTo(fusion8bit, CV_8U);
    // return fusion8bit;

    // hdr
    Mat hdr8bit;
    hdr = hdr * 255;
    hdr.convertTo(hdr8bit, CV_8U);
    return hdr8bit;
}

Let me know if you need any more of my code.

Here is my code to produce the Mat images:

-(cv::Mat)CVMat
{
    CGColorSpaceRef colorSpace = CGImageGetColorSpace(self.CGImage);
    CGFloat cols = self.size.width;
    CGFloat rows = self.size.height;

    cv::Mat cvMat(rows, cols, CV_8UC4); // 8 bits per component, 4 channels

    CGContextRef contextRef = CGBitmapContextCreate(cvMat.data,                 
                                                    cols,                       
                                                    rows,                       
                                                    8,                          
                                                    cvMat.step[0],                                                                      colorSpace,                 
                                                    kCGImageAlphaNoneSkipLast |
                                                    kCGBitmapByteOrderDefault); 

    CGContextDrawImage(contextRef, CGRectMake(0, 0, cols, rows), self.CGImage);
    CGContextRelease(contextRef);

    return cvMat;
}

- (cv::Mat)CVMat3
{
    cv::Mat result = [self CVMat];
    cv::cvtColor(result , result , CV_RGBA2RGB);
    return result;
}  

-(cv::Mat)CVGrayscaleMat
{
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();
    CGFloat cols = self.size.width;
    CGFloat rows = self.size.height;

    cv::Mat cvMat(rows, cols, CV_8UC1); // 8 bits per component, 1 channels

    CGContextRef contextRef = CGBitmapContextCreate(cvMat.data,                 // Pointer to data
                                                    cols,                       // Width of bitmap
                                                    rows,                       // Height of bitmap
                                                    8,                          // Bits per component
                                                    cvMat.step[0],              // Bytes per row
                                                    colorSpace,                 // Colorspace
                                                    kCGImageAlphaNoneSkipLast |
                                                    kCGBitmapByteOrderDefault); // Bitmap info flags

    CGContextDrawImage(contextRef, CGRectMake(0, 0, cols, rows), self.CGImage);
    CGContextRelease(contextRef);
    CGColorSpaceRelease(colorSpace);

    return cvMat;
}

+ (UIImage *)imageWithCVMat:(const cv::Mat&)cvMat
{
    return [[UIImage alloc] initWithCVMat:cvMat];
}

- (id)initWithCVMat:(const cv::Mat&)cvMat
{
    NSData *data = [NSData dataWithBytes:cvMat.data length:cvMat.elemSize() * cvMat.total()];
    CGColorSpaceRef colorSpace;

    size_t elemSize = cvMat.elemSize();
    size_t elemSize1 = cvMat.elemSize1();

    size_t channelCount = elemSize/elemSize1;
    size_t bitsPerChannel = 8 * elemSize1;
    size_t bitsPerPixel = bitsPerChannel * channelCount;

    if (channelCount == 1) {
        colorSpace = CGColorSpaceCreateDeviceGray();
    } else {
        colorSpace = CGColorSpaceCreateDeviceRGB();
    }

    // Tell CGIImageRef different bitmap info if handed 32-bit
    uint32_t bitmapInfo = kCGImageAlphaNone | kCGBitmapByteOrderDefault;

    if (bitsPerChannel == 32 ){
        bitmapInfo = kCGImageAlphaNoneSkipLast | kCGBitmapFloatComponents | kCGBitmapByteOrder32Little;
    }

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

    // Creating CGImage from cv::Mat
    CGImageRef imageRef = CGImageCreate(cvMat.cols,                                 //width
                                        cvMat.rows,                                 //height
                                        bitsPerChannel,                             //bits per component
                                        bitsPerPixel,                               //bits per pixel
                                        cvMat.step[0],                              //bytesPerRow
                                        colorSpace,                                 //colorspace
                                        bitmapInfo,                                 // bitmap info
                                        provider,                                   //CGDataProviderRef
                                        NULL,                                       //decode
                                        false,                                      //should interpolate
                                        kCGRenderingIntentDefault                   //intent
                                        );                     

    // Getting UIImage from CGImage
    self = [self initWithCGImage:imageRef];
    CGImageRelease(imageRef);
    CGDataProviderRelease(provider);
    CGColorSpaceRelease(colorSpace);

    return self;
}