如何以不同的分辨率计算UIImage的裁剪尺寸（rect）

Question

In my app, I have a 'Capture from Camera' function, I am using GPUImageFramework by Brad Larson (ty) , GPUImageStillCamera when capturing still images.

stillCamera = [[GPUImageStillCamera alloc] initWithSessionPreset:AVCaptureSessionPresetPhoto cameraPosition:
               AVCaptureDevicePositionBack];

as you can see. the Session preset is AVCaptureSessionPresetPhoto which in iPhone 4 gives me 1529x2048 output and with 4s (8mp) device gives me 2448x3264.

the image below is how I use the GPUStillCamera. here, there is rectangle which is in this case, the crop rect of the captured image.

code snippet when I capture image.

- (IBAction)takePhoto:(id)sender
{
        [stillCamera capturePhotoAsJPEGProcessedUpToFilter:filter withCompletionHandler:^(NSData *processedJPEG, NSError *error){

        //1529x2048 when iPhone 4 and 2448x3265 when on 4s
        UIImage *rawImage = [[UIImage alloc]initWithCGImage:[[UIImage imageWithData:processedJPEG]CGImage]scale:1.0 orientation:UIImageOrientationUp];

       **CGRect rect = CGRect{?,?,?,?};**
       UIImage *imageFromRect = [rawImage imageAtRect:rect ];
}

My question here is. How can I know the points (x,y,w,h) that I can pass to imageAtRect method that will draw subimage from the rawImage ? and will get only the image portion within the rectangle ( regardless the resolution of the captured image ) as shown in the screen above? should I just do it manually or is there any math technique you can suggest?

Thanks!

Answer 1

You can use this image cropping class and libray file and you can get the size and with and origin position of the cropped UIImage .

http://code4app.net/ios/Custom-image-cropper/51e5f03f6803fac530000000

Plus if you want it can dynamically can change the size of the cropping image accordingly. Easy to use and implement. Please look into the tutorial once.