CODEWITHSUNDEEP
c++iosobjective-copencvuiimage
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Reputation: 3078

Converting to UIImage from cvMat alters image

Whenever I try to convert my binary image back to a UIImage it changes the areas that should be white to a dark blue. I have seen that other people have been having similar issues, but have found no solution.

Here is the code I am using to convert to a UIImage

- (UIImage *)UIImageFromMat:(cv::Mat)image
{

    NSData *data = [NSData dataWithBytes:image.data length:image.elemSize()*image.total()];

    CGColorSpaceRef colorSpace;

    if (image.elemSize() == 1) {
        colorSpace = CGColorSpaceCreateDeviceGray();
    } else {
        colorSpace = CGColorSpaceCreateDeviceRGB();
    }

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

    // Creating CGImage from cv::Mat
    CGImageRef imageRef = CGImageCreate(image.cols,                                 //width
                                        image.rows,                                 //height
                                        8,                                          //bits per component
                                        8 * image.elemSize(),                       //bits per pixel
                                        image.step.p[0],                            //bytesPerRow
                                        colorSpace,                                 //colorspace
                                        kCGImageAlphaNone|kCGBitmapByteOrderDefault,// bitmap info
                                        provider,                                   //CGDataProviderRef
                                        NULL,                                       //decode
                                        false,                                      //should interpolate
                                        kCGRenderingIntentDefault                   //intent
                                        );


    // Getting UIImage from CGImage
    UIImage *finalImage = [UIImage imageWithCGImage:imageRef];
    //[self.imgView setImage:finalImage];
    CGImageRelease(imageRef);
    CGDataProviderRelease(provider);
    CGColorSpaceRelease(colorSpace);

    return finalImage;

}

Can anyone provide some insight as to why my code for converting to a UIImage changes the image? And how to fix it?

Upvotes: 1

Views: 580

Answers (2)

Clip
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Reputation: 3078

Found that I need to apply this code before converting to a UIImage

res.convertTo(res, CV_8UC3, 255.0);

Upvotes: 1

Avt
Avt

Reputation: 17043

I do not know what is the reason but you can fix an image using

CGImageRef CGImageCreateWithMaskingColors (
   CGImageRef image,
   const CGFloat components[]
);

Description Creates a bitmap image by masking an existing bitmap image with the provided color values. Any image sample with color value {c[1], ... c[N]} where min[i] <= c[i] <= max[i] for 1 <= i <= N is masked out (that is, not painted). This means that anything underneath the unpainted samples, such as the current fill color, shows through.

So you will need something like

UIImage *your_image; // do not forget to initialize it
const CGFloat blueMasking[6] = {0.0, 0.05, 0.0, 0.05, 0.95, 1.0};
CGImageRef image = CGImageCreateWithMaskingColors(your_image.CGImage, blueMasking);
UIImage *new_image = [UIImage imageWithCGImage:image];

https://stackoverflow.com/questions/22429538/turn-all-pixels-of-chosen-color-to-white-uiimage/22429897#22429897

Upvotes: 0

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