How to crop the UIImage?

Question

I develop an application in which i process the image using its pixels but in that image processing it takes a lot of time. Therefore i want to crop UIImage (Only middle par

Answer 1

I was looking for a way to get an arbitrary rectangular crop (ie., sub-image) of a UIImage.

Most of the solutions I tried do not work if the orientation of the image is anything but UIImageOrientationUp.

For example:

http://www.hive05.com/2008/11/crop-an-image-using-the-iphone-sdk/

Typically if you use your iPhone camera, you will have other orientations like UIImageOrientationLeft, and you will not get a correct crop with the above. This is because of the use of CGImageRef/CGContextDrawImage which differ in the coordinate system with respect to UIImage.

The code below uses UI* methods (no CGImageRef), and I have tested this with up/down/left/right oriented images, and it seems to work great.

// get sub image
- (UIImage*) getSubImageFrom: (UIImage*) img WithRect: (CGRect) rect {

    UIGraphicsBeginImageContext(rect.size);
    CGContextRef context = UIGraphicsGetCurrentContext();

    // translated rectangle for drawing sub image 
    CGRect drawRect = CGRectMake(-rect.origin.x, -rect.origin.y, img.size.width, img.size.height);

    // clip to the bounds of the image context
    // not strictly necessary as it will get clipped anyway?
    CGContextClipToRect(context, CGRectMake(0, 0, rect.size.width, rect.size.height));

    // draw image
    [img drawInRect:drawRect];

    // grab image
    UIImage* subImage = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return subImage;
}