Question

I’m writing code to use UIImagePickerController. Corey previously posted some nice sample code on SO related to cropping and scaling. However, it doesn’t have implementations of cropImage:to:andScaleTo: nor straightenAndScaleImage().

Here’s how they’re used:

newImage =  [self cropImage:originalImage to:croppingRect andScaleTo:scaledImageSize];
...
UIImage *rotatedImage = straightenAndScaleImage([editInfo objectForKey:UIImagePickerControllerOriginalImage], scaleSize);

Since I’m sure someone must be using something very similar to Corey’s sample code, there’s probably an existing implementation of these two functions. Would someone like to share?

Answer 1

If you check the post you linked to, you’ll see a link to the apple dev forums where I got some of this code, here are the methods you are asking about. Note: I may have made some changes relating to data types, but I can’t quite remember. It should be trivial for you to adjust if needed.

- (UIImage *)cropImage:(UIImage *)image to:(CGRect)cropRect andScaleTo:(CGSize)size {
UIGraphicsBeginImageContext(size);
CGContextRef context = UIGraphicsGetCurrentContext();
CGImageRef subImage = CGImageCreateWithImageInRect([image CGImage], cropRect);
CGRect myRect = CGRectMake(0.0f, 0.0f, size.width, size.height);
CGContextScaleCTM(context, 1.0f, -1.0f);
CGContextTranslateCTM(context, 0.0f, -size.height);
CGContextDrawImage(context, myRect, subImage);
UIImage* croppedImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
CGImageRelease(subImage);
return croppedImage;

}

UIImage *straightenAndScaleImage(UIImage *image, int maxDimension) {

CGImageRef img = [image CGImage];
CGFloat width = CGImageGetWidth(img);
CGFloat height = CGImageGetHeight(img);
CGRect bounds = CGRectMake(0, 0, width, height);
CGSize size = bounds.size;
if (width > maxDimension || height > maxDimension) {
    CGFloat ratio = width/height;
    if (ratio > 1.0f) {
        size.width = maxDimension;
        size.height = size.width / ratio;
    }
    else {
        size.height = maxDimension;
        size.width = size.height * ratio;
    }
} 

CGFloat scale = size.width/width;
CGAffineTransform transform = orientationTransformForImage(image, &size);
UIGraphicsBeginImageContext(size);
CGContextRef context = UIGraphicsGetCurrentContext();
// Flip 
UIImageOrientation orientation = [image imageOrientation];
if (orientation == UIImageOrientationRight || orientation == UIImageOrientationLeft) {

    CGContextScaleCTM(context, -scale, scale);
    CGContextTranslateCTM(context, -height, 0);
}else {
    CGContextScaleCTM(context, scale, -scale);
    CGContextTranslateCTM(context, 0, -height);
}
CGContextConcatCTM(context, transform);
CGContextDrawImage(context, bounds, img);
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return newImage;

}