Auto Enhancement Filters

Table 3-1 shows the filters Core Image uses for automatically enhancing images. These filters remedy some of the most common issues found in photos.

Using Auto Enhancement Filters

The auto enhancement API has only two methods: autoAdjustmentFilters and autoAdjustmentFiltersWithOptions:. In most cases, you’ll want to use the method that provides an options dictionary.

You can set these options:

• The image orientation, which is important for the CIRedEyeCorrection and CIFaceBalance filters, so that Core Image can find faces accurately.

• Whether to apply only red eye correction. (Set kCIImageAutoAdjustEnhance to false.)

• Whether to apply all filters except red eye correction. (Set kCIImageAutoAdjustRedEye to false.)

The autoAdjustmentFiltersWithOptions: method returns an array of options filters that you’ll then want to chain together and apply to the analyzed image, as shown in Listing 3-1. The code first creates an options dictionary. It then gets the orientation of the image and sets that as the value for the key CIDetectorImageOrientation.

Listing 3-1  Getting auto enhancement filters and applying them to an image

NSDictionary *options = @{ CIDetectorImageOrientation :

                 [[image properties] valueForKey:kCGImagePropertyOrientation] };

NSArray *adjustments = [myImage autoAdjustmentFiltersWithOptions:options];

for (CIFilter *filter in adjustments) {

     [filter setValue:myImage forKey:kCIInputImageKey];

     myImage = filter.outputImage;

}

Recall that the input parameter values are already set by Core Image to produce the best result.

You don’t have to apply the auto adjustment filters right away. You can save the filter names and parameter values for later. Saving them allows your app to perform the enhancements later without the cost of analyzing the image again.