将CUSTOM元数据保存在iOS中从AVFoundation拍摄的图像中

Question

How do I save custom metadata in an image when i get the image using the AVFoundation framework ?

I know I can access the properties weather it I have my image as UIImage or CIImage but the properties that these seem to have differ from each other (even if it is the same image).

So far I access the dictionary like this: (Code taken from Caffeinated Cocoa blog)

NSLog(@"about to request a capture from: %@", [self stillImageOutput]);
    [[self stillImageOutput] captureStillImageAsynchronouslyFromConnection:videoConnection completionHandler:^(CMSampleBufferRef imageSampleBuffer, NSError *error) 
    {

NSData *jpeg = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageSampleBuffer] ;

        CGImageSourceRef source = CGImageSourceCreateWithData((__bridge_retained  CFDataRef)jpeg, NULL);

        //get all the metadata in the image
        NSDictionary *metadata = (__bridge NSDictionary *) CGImageSourceCopyPropertiesAtIndex(source,0,NULL);

        //make the metadata dictionary mutable so we can add properties to it
        NSMutableDictionary *metadataAsMutable = [metadata mutableCopy];

        NSMutableDictionary *EXIFDictionary = [[metadataAsMutable objectForKey:(NSString *)kCGImagePropertyExifDictionary]mutableCopy];
        NSMutableDictionary *GPSDictionary = [[metadataAsMutable objectForKey:(NSString *)kCGImagePropertyGPSDictionary]mutableCopy];
        NSMutableDictionary *RAWDictionary = [[metadataAsMutable objectForKey:(NSString *)kCGImagePropertyRawDictionary]mutableCopy];

        if(!EXIFDictionary) {
            EXIFDictionary = [NSMutableDictionary dictionary];
        }
        if(!GPSDictionary) {
            GPSDictionary = [NSMutableDictionary dictionary];
        }
        if(!RAWDictionary) {
            RAWDictionary = [NSMutableDictionary dictionary];
        }

        float _lat = gpsInfo.coordinate.latitude;
        float _lon = gpsInfo.coordinate.longitude;
        float _alt = gpsInfo.altitude;
        NSDate *_date = gpsInfo.timestamp;
        float _heading = gpsInfo.course;;

        [GPSDictionary setValue:[NSNumber numberWithFloat:_lat] 
                         forKey:(NSString*)kCGImagePropertyGPSLatitude];
        [GPSDictionary setValue:[NSNumber numberWithFloat:_lon] 
                         forKey:(NSString*)kCGImagePropertyGPSLongitude];
        [GPSDictionary setValue:[NSNumber numberWithFloat:_alt] 
                         forKey:(NSString*)kCGImagePropertyGPSAltitude];
        [GPSDictionary setValue:_date 
                         forKey:(NSString*)kCGImagePropertyGPSDateStamp];
        [GPSDictionary setValue:[NSNumber numberWithFloat:_heading] 
                         forKey:(NSString*)kCGImagePropertyGPSImgDirection];


        [EXIFDictionary setValue:@"Wasup" forKey:(NSString *)kCGImagePropertyExifUserComment];

        [RAWDictionary setValue:attitude forKey:@"Attitude"];

        //Add the modified Data back into the image’s metadata
        [metadataAsMutable setObject:EXIFDictionary forKey:(NSString *)kCGImagePropertyExifDictionary];
        [metadataAsMutable setObject:GPSDictionary forKey:(NSString *)kCGImagePropertyGPSDictionary];
        [metadataAsMutable setObject:RAWDictionary forKey:(NSString *)kCGImagePropertyRawDictionary];

        NSLog(@"Info: %@",metadataAsMutable);

        CFStringRef UTI = CGImageSourceGetType(source); //this is the type of image (e.g., public.jpeg)

        //this will be the data CGImageDestinationRef will write into
        NSMutableData *data = [NSMutableData data];

        CGImageDestinationRef destination = CGImageDestinationCreateWithData((__bridge CFMutableDataRef)data,UTI,1,NULL);

        if(!destination) {
            NSLog(@"***Could not create image destination ***");
        }

        //add the image contained in the image source to the destination, overidding the old metadata with our modified metadata

        CGImageDestinationAddImageFromSource(destination,source,0, (__bridge CFDictionaryRef) metadataAsMutable);

        //tell the destination to write the image data and metadata into our data object.
        //It will return false if something goes wrong
        BOOL success = NO;
        success = CGImageDestinationFinalize(destination);

        if(!success) {
            NSLog(@"***Could not create data from image destination ***");
        }

And i can either save my image like this:

CIImage *testImage = [CIImage imageWithData:data];

        NSDictionary *propDict = [testImage properties];


        NSLog(@"Properties %@",propDict);

Or like this

UIImage *imageMod = [[UIImage alloc] initWithData:data];


CGImageSourceRef source2 = CGImageSourceCreateWithData((__bridge CFDataRef)data, NULL);

        //get all the metadata in the image
NSDictionary *metadata2 = (__bridge NSDictionary *) CGImageSourceCopyPropertiesAtIndex(source2,0,NULL);

NSLog(@"WASD: %@",metadata2);

BUt neither of the options return my Custom Raw Data Dictionary.

In summary what i want to do is save my own object in a field created by myself (in this case a cmattitude object)

PD: When i NSLOG the dictionary before merging it with the image it does have all the files like i want them.

Info: {
    ColorModel = RGB;
    DPIHeight = 72;
    DPIWidth = 72;
    Depth = 8;
    Orientation = 6;
    PixelHeight = 1080;
    PixelWidth = 1920;
    "{Exif}" =     {
        ApertureValue = "2.526069";
        BrightnessValue = "4.013361";
        ColorSpace = 1;
        ComponentsConfiguration =         (
            1,
            2,
            3,
            0
        );
        ExifVersion =         (
            2,
            2,
            1
        );
        ExposureMode = 0;
        ExposureProgram = 2;
        ExposureTime = "0.03333334";
        FNumber = "2.4";
        Flash = 16;
        FlashPixVersion =         (
            1,
            0
        );
        FocalLenIn35mmFilm = 35;
        FocalLength = "4.28";
        ISOSpeedRatings =         (
            80
        );
        MeteringMode = 5;
        PixelXDimension = 1920;
        PixelYDimension = 1080;
        SceneCaptureType = 0;
        SensingMethod = 2;
        Sharpness = 0;
        ShutterSpeedValue = "4.906905";
        SubjectArea =         (
            959,
            539,
            518,
            388
        );
        UserComment = "Wazup";
        WhiteBalance = 0;
    };
    "{GPS}" =     {
        Altitude = 102;
        DateStamp = "2012-01-20 06:55:48 +0000";
        ImgDirection = "-1";
        Latitude = "35.02496";
        Longitude = "135.754";
    };
    "{Raw}" =     {
        Attitude = "Pitch: 50.913760, Roll: 36.342350, Yaw: -164.272361 @ 0.048291\n";
    };
    "{TIFF}" =     {
        Orientation = 6;
        ResolutionUnit = 2;
        XResolution = 72;
        YResolution = 72;
        "_YCbCrPositioning" = 1;
    };

But when i NSLOG the dictionary from the new image it gives me this for the CIIMage:

Properties {
    ColorModel = RGB;
    DPIHeight = 72;
    DPIWidth = 72;
    Depth = 8;
    Orientation = 6;
    PixelHeight = 1080;
    PixelWidth = 1920;
    "{Exif}" =     {
        ApertureValue = "2.526069";
        BrightnessValue = "4.013361";
        ColorSpace = 1;
        ComponentsConfiguration =         (
            0,
            0,
            0,
            1
        );
        ExifVersion =         (
            2,
            2,
            1
        );
        ExposureMode = 0;
        ExposureProgram = 2;
        ExposureTime = "0.03333334";
        FNumber = "2.4";
        Flash = 16;
        FlashPixVersion =         (
            1,
            0
        );
        FocalLenIn35mmFilm = 35;
        FocalLength = "4.28";
        ISOSpeedRatings =         (
            80
        );
        MeteringMode = 5;
        PixelXDimension = 1920;
        PixelYDimension = 1080;
        SceneCaptureType = 0;
        SensingMethod = 2;
        Sharpness = 0;
        ShutterSpeedValue = "4.906905";
        SubjectArea =         (
            959,
            539,
            518,
            388
        );
        UserComment = "Wazup";
        WhiteBalance = 0;
    };
    "{GPS}" =     {
        Altitude = 102;
        ImgDirection = 0;
        Latitude = "35.025";
        Longitude = "135.754";
    };
    "{JFIF}" =     {
        DensityUnit = 1;
        JFIFVersion =         (
            1,
            1
        );
        XDensity = 72;
        YDensity = 72;
    };
    "{TIFF}" =     {
        Orientation = 6;
        ResolutionUnit = 2;
        XResolution = 72;
        YResolution = 72;
        "_YCbCrPositioning" = 1;
    };

And if I NSLog the UIImage it gives me even less info.

Thanks!

Answer 1

UIImage and CIImage don't hold all the metadata. In fact, converting it from NSData to either of those two formats will strip a lot of that metadata out, so IMHO, UIImage and CIImage should only be used if you are planning on displaying it in the UI or passing it to CoreImage .

You can read the image properties like this:

- (NSDictionary *)getImageProperties:(NSData *)imageData {
    // get the original image metadata
    CGImageSourceRef imageSourceRef = CGImageSourceCreateWithData((__bridge CFDataRef) imageData, NULL);
    CFDictionaryRef properties = CGImageSourceCopyPropertiesAtIndex(imageSourceRef, 0, NULL);
    NSDictionary *props = (__bridge_transfer NSDictionary *) properties;
    CFRelease(imageSourceRef);

    return props;
}

You can then convert your NSDictionary to a NSMutableDictionary :

NSDictionary *props = [self getImageProperties:imageData];
NSMutableDictionary *mutableDictionary = [NSMutableDictionary dictionaryWithDictionary:props];

After that, add whatever fields you would like. Note that EXIF data is found by grabbing the kCGImagePropertyExifDictionary , GPS data by the kCGImagePropertyGPSDictionary , and so on:

NSMutableDictionary *exifDictionary = properties[(__bridge NSString *) kCGImagePropertyExifDictionary];

Look at the CGImageProperties header file for all the keys available.

Okay, so now that you have made whatever changes you needed to the metadata, adding it back takes a couple of more steps:

// incoming image data
NSData *imageData;

// create the image ref
CGDataProviderRef imgDataProvider = CGDataProviderCreateWithCFData((__bridge CFDataRef) imageData);
CGImageRef imageRef = CGImageCreateWithJPEGDataProvider(imgDataProvider, NULL, true, kCGRenderingIntentDefault);

// the updated properties from above
NSMutableDictionary *mutableDictionary;

// create the new output data
CFMutableDataRef newImageData = CFDataCreateMutable(NULL, 0);
// my code assumes JPEG type since the input is from the iOS device camera
CFStringRef type = UTTypeCreatePreferredIdentifierForTag(kUTTagClassMIMEType, (__bridge CFStringRef) @"image/jpg", kUTTypeImage);
// create the destination
CGImageDestinationRef destination = CGImageDestinationCreateWithData(newImageData, type, 1, NULL);
// add the image to the destination
CGImageDestinationAddImage(destination, imageRef, (__bridge CFDictionaryRef) mutableDictionary);
// finalize the write
CGImageDestinationFinalize(destination);

// memory cleanup
CGDataProviderRelease(imgDataProvider);
CGImageRelease(imageRef);
CFRelease(type);
CFRelease(destination);

// your new image data
NSData *newImage = (__bridge_transfer NSData *)newImageData;

And there you have it.