Cropping center square of UIImage

Question

So here\'s where I\'ve made it so far. I am using a UIImage captured from the camera and can crop the center square when in landscape. For some reason this doesn\'t transl

Answer 1

This is an old question, but none of the answers are really correct (even the accepted answer). The important thing to understand is that UIImageOrientation (image.imageOrientation) is actually correct, but it's definition of UP and our definition of UP are different. For us, UP is the top of the device (where the power button is). For UIImageOrientation, UP is the side opposite of the volume control buttons. So if the device takes a picture with the volume controls down, this is UIImageOrientationUp. If you take a picture in portrait mode (with the home button down), this is UIImageOrientationLeft.

So you can calculate the center in portrait, then you can apply the following transform to the image so that the crop is in the correct place.

- (UIImage *)cropImage:(UIImage*)image toRect:(CGRect)rect {
    CGFloat (^rad)(CGFloat) = ^CGFloat(CGFloat deg) {
        return deg / 180.0f * (CGFloat) M_PI;
    };

    // determine the orientation of the image and apply a transformation to the crop rectangle to shift it to the correct position
    CGAffineTransform rectTransform;
    switch (image.imageOrientation) {
        case UIImageOrientationLeft:
            rectTransform = CGAffineTransformTranslate(CGAffineTransformMakeRotation(rad(90)), 0, -image.size.height);
            break;
        case UIImageOrientationRight:
            rectTransform = CGAffineTransformTranslate(CGAffineTransformMakeRotation(rad(-90)), -image.size.width, 0);
            break;
        case UIImageOrientationDown:
            rectTransform = CGAffineTransformTranslate(CGAffineTransformMakeRotation(rad(-180)), -image.size.width, -image.size.height);
            break;
        default:
            rectTransform = CGAffineTransformIdentity;
    };

    // adjust the transformation scale based on the image scale
    rectTransform = CGAffineTransformScale(rectTransform, image.scale, image.scale);

    // apply the transformation to the rect to create a new, shifted rect
    CGRect transformedCropSquare = CGRectApplyAffineTransform(rect, rectTransform);
    // use the rect to crop the image
    CGImageRef imageRef = CGImageCreateWithImageInRect(image.CGImage, transformedCropSquare);
    // create a new UIImage and set the scale and orientation appropriately
    UIImage *result = [UIImage imageWithCGImage:imageRef scale:image.scale orientation:image.imageOrientation];
    // memory cleanup
    CGImageRelease(imageRef);

    return result;
}

This code shifts the crop square so that it is in the correct relative position.