如何在iPhone中按比例裁剪图像？

Question

I have a large sized image (2048*2048px), this image is shown as 320*320 on iPhone screen. I want to do this:

In my APP, user can open large sized image(eg 2048*2048), the image is shown as 320*320 on iPhone screen, and there is rectangle over the image, user can move the rectangle anywhere within image on iPhone screen, eg rectangle(100, 100, 300, 200), then I want to clip the original sized image within the rectangle area in scale.

I tried many ways,

UIImageView *originalImageView = [[UIImage View alloc] initWithImage:originalImage]];

CGRect rect = CGRectMake(100, 100, 300, 200);

UIImage *cropImage = [UIImage imageWithCGImage:CGImageCreateWithImageInRect([originalImageView.image CGImage], rect)];

But I got the cropImage is just 300*200 sized image, not scale properly.

Answer 1

How about doing this, it will preserve the original image quality

CGSize bounds = CGSizeMake(320,320) // Considering image is shown in 320*320
CGRect rect = CGRectMake(100, 100, 220, 200); //rectangle area to be cropped

float widthFactor = rect.size.width * (originalImage.size.width/bounds.size.width);
float heightFactor = rect.size.height * (originalImage.size.height/bounds.size.height);
float factorX = rect.origin.x * (originalImage.size.width/bounds.size.width);
float factorY = rect.origin.y * (originalImage.size.height/bounds.size.height);

CGRect factoredRect = CGRectMake(factorX,factorY,widthFactor,heightFactor);
UIImage *cropImage = [UIImage imageWithCGImage:CGImageCreateWithImageInRect([originalImage CGImage], factoredRect)];

And most importantly if you want to crop image that imagePickerController returns, then this can be done by built in function as below,

imagePickerController.allowsEditing = YES;

Answer 2

Why not calculate the scale factor (eg originalImageWidth/smallImageWidth)? If the rectangle is (100,100,300,200) in your small image, you should clip your lage image at size (100*factor,100*factor,300*factor,200*factor) .

Answer 3

Firstly resize image with size 320*320 using this method:

+(UIImage *)resizeImage:(UIImage *)image width:(float)width height:(float)height
{
  CGSize newSize;
  newSize.width = width;
  newSize.height = height
  UIGraphicsBeginImageContext(newSize);
  [image drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];
  UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext();
}

Now set resized image in imageView

UIImage *resizeImage = [YourControllerName resizeImage:originalImage width:320 height:320];
UIImageView *originalImageView = [[UIImage View alloc] initWithImage:resizeImage]];

You can now crop

CGRect rect = CGRectMake(100, 100, 300, 200);
UIImage *cropImage = [UIImage imageWithCGImage:CGImageCreateWithImageInRect([originalImageView.image CGImage], rect)];