How to crop the UIImage?

Question

Hi, 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 part of image i.e. removing/croping bordered part of image).I have the develop code are, - (NSInteger) processImage1: (UIImage*) image {

CGFloat width = image.size.width; CGFloat height = image.size.height; struct pixel* pixels = (struct pixel*) calloc(1, image.size.width * image.size.height * sizeof(struct pixel)); if (pixels != nil) { // Create a new bitmap CGContextRef context = CGBitmapContextCreate( (void*) pixels, image.size.width, image.size.height, 8, image.size.width * 4, CGImageGetColorSpace(image.CGImage), kCGImageAlphaPremultipliedLast ); if (context != NULL) { // Draw the image in the bitmap CGContextDrawImage(context, CGRectMake(0.0f, 0.0f, image.size.width, image.size.height), image.CGImage); NSUInteger numberOfPixels = image.size.width * image.size.height;

NSMutableArray *numberOfPixelsArray = [[[NSMutableArray alloc] initWithCapacity:numberOfPixelsArray] autorelease]; }

How i take(croping outside bordered) the middle part of UIImage?????????

Answer 1

try something like

CGImageRef imageRef = CGImageCreateWithImageInRect([largeImage CGImage], cropRect);

image = [UIImage imageWithCGImage:imageRef]]; 
CGImageRelease(imageRef);

cropRect is Smaller Rectangle with middle part of the image...

Answer 2

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;
}