NSImage *img = [[NSImage alloc] initWithContentsOfFile:filename];
  NSArray *reps = [img representations];
  NSBitmapImageRep *rep = reps ? [reps objectAtIndex:0] : 0;
  if (rep) {
    NSDictionary *exif = [rep valueForProperty: @"NSImageEXIFData"];
    if (exif) {
      NSString *rot = [exif objectForKey:@"Orientation"];
      NSLog (@"rot = %@", rot);
      NSEnumerator *e = [exif keyEnumerator];
      id key;
      while ((key = [e nextObject])) {
        NSLog (@"%@ = %@", key, [exif objectForKey:key]);
      }
    }
  }

8 Responses:

1. scullin says:

   14 years ago at 4:17 pm

   I have to say it's creepy that when i google "NSImageEXIFData Orientation", this is the first result.

2. poon says:

   14 years ago at 4:21 pm

   Cocoa provides no love.

   Using libexif from http://sf.net/projects/libexif :

   
   #include <stdio.h>
   #include <stdlib.h>
   #include <libexif/exif-data.h>
   
   int
   main(int argc, char *argv[]) {
     if(argc != 2) {
       printf("Usage: foo <image>\n");
       exit(1);
     }
   
     int orientation = 0;
     ExifData *exifData = exif_data_new_from_file(argv[1]);
     if (exifData) {
       ExifByteOrder byteOrder = exif_data_get_byte_order(exifData);
       ExifEntry *exifEntry = exif_data_get_entry(exifData,
                                                  EXIF_TAG_ORIENTATION);
       if (exifEntry)
         orientation = exif_get_short(exifEntry->data, byteOrder);
   
       exif_data_free(exifData);
     }
   
     /*
           0th Row      0th Column
        1  top          left side
        2  top          right side
        3  bottom       right side
        4  bottom       left side
        5  left side    top
        6  right side   top
        7  right side   bottom
        8  left side    bottom
     */
   
     if(orientation != 0) {
       printf("orientation == %d\n", orientation);
     }
   
     exit(0);
   }
   
   

   • jwz says:

     14 years ago at 4:25 pm

     Well that's just silly. Finder and Preview are accomplishing it somehow, and they aren't using libexif to do it.

     • poon says:

       14 years ago at 5:26 pm

       Alright, alright.

       
       #import <Cocoa/Cocoa.h>
       
       int main (int argc, char *argv[])
       {
         NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
         NSString *filename = [NSString stringWithCString:argv[1]];
         NSData *imageData = [[NSData alloc] initWithContentsOfFile:filename];
         NSImage *image = [[NSImage alloc] initWithData:imageData];
       
         if(!image)
           return 0;
       
         CGImageSourceRef imageSource =
           CGImageSourceCreateWithData ((CFDataRef)imageData, NULL);
       
         CGImageRef imageRef = CGImageSourceCreateImageAtIndex(imageSource, 0, NULL);
       
         CFDictionaryRef properties = CGImageSourceCopyPropertiesAtIndex(imageSource,
                                                                         0, NULL);
       
         NSLog(@"orientation == %@",
               CFDictionaryGetValue(properties, kCGImagePropertyOrientation));
       
         [pool drain];
         return 0;
       }
       

       • tooluser says:

         14 years ago at 9:16 am

         What, were you just waiting for him to complain hard enough? We can probably take that for granted.

         Thanks, I was curious about this, too.

3. bovinity says:

   14 years ago at 4:41 pm

   The ImageIO framework is the way to go - http://phughes.us/node/2 has some sample code.

   GraphicsImaging/Reference/CGImageProperties_Reference/Reference/reference.html has all the keys, of which kCGImagePropertyOrientation is the one you're looking for.

4. sol3 says:

   14 years ago at 4:44 pm

   It looks like you want to be using ImageIO framework. Specifically a CGImageSource object, and one of the properties that you can pull out is kCGImagePropertyOrientation.

5. endquote says:

   14 years ago at 8:16 pm

   I've seen a bunch of apps get exif rotation wrong, including ones published by Flickr, so I guess it's sort of good to hear that it's not a total no-brainer to implement.