Creating a thumbnail from UIImage using CGImageSourceCreateThumbnailAtIndex

I want to use the function CGImageSourceCreateThumbnailAtIndex to create a thumbnail from an UIImage. All I have is the UIImage itself. The image is the snapshot on a UIView.

Please, I don't want to use any other method to create the thumbnail, just the one using CGImageSourceCreateThumbnailAtIndex, because I want to compare its performance with the other methods I already have.

Said that, this is the code I have so far.

I have create a UIImage category with this code:

- (UIImage *)createSquaredThumbnailWithWidth:(NSInteger)width {

  CFDictionaryRef options = (__bridge CFDictionaryRef) @{
                                                         (id) kCGImageSourceCreateThumbnailWithTransform : @YES,
                                                         (id) kCGImageSourceCreateThumbnailFromImageAlways : @YES,
                                                         (id) kCGImageSourceThumbnailMaxPixelSize : @(width)
                                                         };

  CGImageRef scaledImageRef = CGImageSourceCreateThumbnailAtIndex(????, 0, options);


  UIImage* scaled = [UIImage imageWithCGImage:scaledImageRef];

  CGImageRelease(scaledImageRef);

  return scaled;
}

My problem is with this line:

  CGImageRef scaledImageRef = CGImageSourceCreateThumbnailAtIndex(????, 0, options);

The first parameter of this function demands a CGImageSourceRef, but like I said, I just have an UIImage, that image is on memory, not on disk, and I don't want to save it to disk, or the performance will go down the drain.

How do I get a CGImageSourceRef from a UIImage that is on memory???

Solution

Have you try using CGImageSourceCreateWithData and passing image data as CFDataRef like this:

Note: Using CGImageSourceCreateWithData loses information about image rotation, use the CGImageSourceCreateWithURL for hassle free rotation of final image.

NSData *imageData = UIImagePNGRepresentation(image);
CGImageSourceRef src = CGImageSourceCreateWithData((__bridge CFDataRef)imageData, NULL);
CFDictionaryRef options = (__bridge CFDictionaryRef) @{
                                                     (id) kCGImageSourceCreateThumbnailWithTransform : @YES,
                                                     (id) kCGImageSourceCreateThumbnailFromImageAlways : @YES,
                                                     (id) kCGImageSourceThumbnailMaxPixelSize : @(width)
                                                     };

CGImageRef scaledImageRef = CGImageSourceCreateThumbnailAtIndex(src, 0, options);
CFRelease(src);
UIImage *scaled = [UIImage imageWithCGImage:scaledImageRef];
CGImageRelease(scaledImageRef);
return scaled;

Note: If you have URL of image then you can create CGImageSourceRef using CGImageSourceCreateWithURL.

CGImageSourceRef src = CGImageSourceCreateWithURL((__bridge CFURLRef)(imageFileURL), NULL);