How to fetch squared thumbnails from PHImageManager?

Question

Has anybody idea how to fetch squared thumbs from PHImageManager? PHImageContentModeAspectFill option has no effect.

[[PHImageManager defaultManager]
  requestIm         


        

Answer 1

Update:

The bug in cropping images as they were retrieved from PHImageManager was fixed in iOS 8.3, so for that version of iOS and later, my original example works, as follows: It seems the bugs are still there up to and including iOS 8.4, I can reproduce them with standard iPhone 6s back camera images, taking a full size square crop. They are properly fixed in iOS 9.0, where even large crops of a 63 megapixel panorama work fine.

The approach Apple defines is to pass a CGRect in the co-ordinate space of the image, where the origin is (0,0) and the maximum is (1,1). You pass this rect in the PHImageRequestOptions object, along with a resizeMode of PHImageRequestOptionsResizeModeExact, and then you should get back a cropped image.

- (void)showSquareImageForAsset:(PHAsset *)asset
{
    NSInteger retinaScale = [UIScreen mainScreen].scale;
    CGSize retinaSquare = CGSizeMake(100*retinaScale, 100*retinaScale);

    PHImageRequestOptions *cropToSquare = [[PHImageRequestOptions alloc] init];
    cropToSquare.resizeMode = PHImageRequestOptionsResizeModeExact;

    CGFloat cropSideLength = MIN(asset.pixelWidth, asset.pixelHeight);
    CGRect square = CGRectMake(0, 0, cropSideLength, cropSideLength);
    CGRect cropRect = CGRectApplyAffineTransform(square,
                                                 CGAffineTransformMakeScale(1.0 / asset.pixelWidth,
                                                                            1.0 / asset.pixelHeight));

    cropToSquare.normalizedCropRect = cropRect;

    [[PHImageManager defaultManager]
     requestImageForAsset:(PHAsset *)asset
     targetSize:retinaSquare
     contentMode:PHImageContentModeAspectFit
     options:cropToSquare
     resultHandler:^(UIImage *result, NSDictionary *info) {
         self.imageView.image = result;
     }];
}

This example makes its cropRect of side length equal to the smaller of the width and height of the asset, and then transforms it to the co-ordinate space of the image using CGRectApplyAffineTransform. You may want to set the origin of square to something other than (0,0), as often you want the crop square centred along the axis of the image which is being cropped, but I'll leave that as an exercise for the reader. :-)

Original Answer:

John's answer got me most of the way there, but using his code I was getting stretched and squashed images. Here's how I got an imageView to display square thumbnails fetched from the PHImageManager.

Firstly, ensure that the contentMode property for your UIImageView is set to ScaleAspectFill. The default is to ScaleToFill, which doesn't work correctly for displaying square thumbnails from PHImageManager, so make sure you change this whether you've instantiated the UIImageView in code or in the storyboard.

//view dimensions are based on points, but we're requesting pixels from PHImageManager
NSInteger retinaMultiplier = [UIScreen mainScreen].scale;
CGSize retinaSquare = CGSizeMake(imageView.bounds.size.width * retinaMultiplier, imageView.bounds.size.height * retinaMultiplier);

[[PHImageManager defaultManager]
     requestImageForAsset:(PHAsset *)_asset
               targetSize:retinaSquare
              contentMode:PHImageContentModeAspectFill
                  options:nil
            resultHandler:^(UIImage *result, NSDictionary *info) {

    // The result is not square, but correctly displays as a square using AspectFill
    imageView.image = result;
}];

Specifying PHImageRequestOptionsResizeModeExact for the resizeMode is not required, as it will not give you a cropped image unless you also supply a normalizedCropRect, and should not be used here as there's no benefit, and using it means you don't get the benefits of quickly returned cached images.

The UIImage returned in result will be the same aspect ratio as the source, but scaled correctly for use in a UIImageView which is set to aspect fill to display as a square, so if you're just displaying it, this is the way to go. If you need to crop the image for print or export outside of the app, this isn't what you want - look into the use of normalizedCropRect for that. (edit- see below for example of what should work...)

Except this also make sure that the you set the content mode of the UIImageView to UIViewContentModeScaleAspectFill and that you set clipsToBounds = YES by the following 2 lines :

imageView.contentMode=UIViewContentModeScaleAspectFill;
imageView.clipsToBounds=YES;

---

Edit to add normalizedCropRect usage example
WARNING - this doesn't work, but should according to Apple's documentation.

The approach Apple defines is to pass a CGRect in the co-ordinate space of the image, where the origin is (0,0) and the maximum is (1,1). You pass this rect in the PHImageRequestOptions object, along with a resizeMode of PHImageRequestOptionsResizeModeExact, and then you should get back a cropped image. The problem is that you don't, it comes back as the original aspect ratio and the full image.

I've verified that the crop rect is created correctly in the image's co-ordinate space, and followed the instruction to use PHImageRequestOptionsResizeModeExact, but the result handler will still be passed an image in the original aspect ratio. This seems to be a bug in the framework, and when it is fixed, the following code should work.

- (void)showSquareImageForAsset:(PHAsset *)asset
{
    NSInteger retinaScale = [UIScreen mainScreen].scale;
    CGSize retinaSquare = CGSizeMake(100*retinaScale, 100*retinaScale);

    PHImageRequestOptions *cropToSquare = [[PHImageRequestOptions alloc] init];
    cropToSquare.resizeMode = PHImageRequestOptionsResizeModeExact;

    CGFloat cropSideLength = MIN(asset.pixelWidth, asset.pixelHeight);
    CGRect square = CGRectMake(0, 0, cropSideLength, cropSideLength);
    CGRect cropRect = CGRectApplyAffineTransform(square,
                                                 CGAffineTransformMakeScale(1.0 / asset.pixelWidth,
                                                                            1.0 / asset.pixelHeight));

    cropToSquare.normalizedCropRect = cropRect;

    [[PHImageManager defaultManager]
     requestImageForAsset:(PHAsset *)asset
     targetSize:retinaSquare
     contentMode:PHImageContentModeAspectFit
     options:cropToSquare
     resultHandler:^(UIImage *result, NSDictionary *info) {
         self.imageView.image = result;
     }];
}

All I can suggest is that if you have this problem, you file a radar with Apple to request that they fix it!