Accessing image properties with ImageIO

Q:  How can I access image properties, such as image height and width, DPI, EXIF data, etc., of an image?

A: How can I access image properties, such as image height and width, DPI, EXIF data, etc., of an image?

The ImageIO framework, which was introduced on the Mac in Mac OS X 10.4 and on iOS in iOS4, provides the capabilities to access image properties such as size, DPI, EXIF data, etc. from an image.

To access the image properties you:

1. create a CGImageSourceRef for your image.

2. get a copy of the image properties dictionary by calling CGImageSourceCopyPropertiesAtIndex.

3. access the values in the dictionary by calling CFDictionaryGetValue with the property key that you are interested in. The available keys are located in the CGImageProperties Reference.

Below is an example of how to access the width and height of an image.

Listing 1  Accessing image width and height.

CFURLRef url = CFURLCreateFromFileSystemRepresentation (kCFAllocatorDefault, (const UInt8 *)inputFileName, strlen(inputFileName), false);

if (!url) {
   printf ("* * Bad input file path\n"); 
}

CGImageSourceRef myImageSource;

myImageSource = CGImageSourceCreateWithURL(url, NULL);

CFDictionaryRef imagePropertiesDictionary;

imagePropertiesDictionary = CGImageSourceCopyPropertiesAtIndex(myImageSource,0, NULL);

CFNumberRef imageWidth = (CFNumberRef)CFDictionaryGetValue(imagePropertiesDictionary, kCGImagePropertyPixelWidth);
CFNumberRef imageHeight = (CFNumberRef)CFDictionaryGetValue(imagePropertiesDictionary, kCGImagePropertyPixelHeight);

int w = 0;
int h = 0;

CFNumberGetValue(imageWidth, kCFNumberIntType, &w);
CFNumberGetValue(imageHeight, kCFNumberIntType, &h);

CFRelease(imagePropertiesDictionary);
CFRelease(myImageSource);

printf("Image Width: %d\n",w);
printf("Image Height: %d\n",h);

For more information about using the ImageIO Framework, please see Using the ImageIO Framework.

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