Crop and Scale CGContext - iOS

gistfile1.m

//Crop and Scale CGContext - iOS
//http://pastebin.com/8xWrr1tv
- (void)modifyImage:(CMSampleBufferRef) sampleBuffer {
    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer); 

    // Lock the image buffer
    CVPixelBufferLockBaseAddress(imageBuffer,0); 

    // Get information about the image
    uint8_t *baseAddress = (uint8_t *)CVPixelBufferGetBaseAddress(imageBuffer); 
    size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer); 
    size_t width = CVPixelBufferGetWidth(imageBuffer); 
    size_t height = CVPixelBufferGetHeight(imageBuffer); 

    // Create a CGImageRef from the CVImageBufferRef
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); 
    CGContextRef context = CGBitmapContextCreate(baseAddress, width, height, 8, bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst); 

    CGContextSaveGState(context);

    CGContextSetFillColorWithColor(context, [[UIColor blackColor] CGColor]);
    CGContextFillRect(context, CGRectMake(0, 0, 400, 400));

    //restore the context and remove the clipping area.
    CGContextRestoreGState(context);


    // We unlock the image buffer
    CVPixelBufferUnlockBaseAddress(imageBuffer,0);

    // We release some components
    CGContextRelease(context); 
    CGColorSpaceRelease(colorSpace);
    return;
}