你如何覆蓋圖像元數據？

Question

如果key/val已經存在於使用CGImageDestination的原始圖像元數據中，我似乎無法正確地將圖像元數據寫入圖像。它工作得很好，如果它的key/val不存在於原始的元數據中。

就好像原始圖像中的圖像元數據屬性優先於修改。這是一種拜占庭式的格式問題，我不知道，我需要以某種不尋常的方式填充key/val，一個bug，或者？其他人看過這個？

下面的代碼和輸出，適用於正常工作（如果該值尚未設置）和寫入失敗（如果該值已設置爲其他值）的兩種情況。

任何幫助表示非常感謝。

這裏就是/ I如何創建圖像的NSData：

// convert the existing asset to nsdata to overwrite itself 
ALAssetRepresentation* rep = [asset defaultRepresentation]; 
Byte* buffer    = (Byte*)malloc(rep.size); 
NSUInteger buffered  = [rep getBytes:buffer fromOffset:0.0 length:rep.size error:nil]; 
NSData* imageData   = [NSData dataWithBytesNoCopy:buffer length:buffered freeWhenDone:YES]; 

// write the metadata directly into the nsdata of the image itself 
NSData* newImage = [self writeMetadataIntoImageData:imageData metadata:newMetadata]; 

這裏是所述元數據的實際的修改：

- (NSData*)writeMetadataIntoImageData:(NSData*)imageData metadata:(NSMutableDictionary*)metadataAsMutable 
{ 
    // create an imagesourceref 
    CGImageSourceRef source = CGImageSourceCreateWithData((__bridge CFDataRef) imageData, NULL); 

    // read and log pre write metadata 
    NSDictionary* metadata = (NSDictionary *) CFBridgingRelease(CGImageSourceCopyPropertiesAtIndex(source,0,NULL)); 
    NSLog(@"Before:\n------------------------------%@\n------------------------------", metadata); 

    // set the new metadata keys here 
    NSMutableDictionary* iptc = [metadataAsMutable[(NSString*)kCGImagePropertyIPTCDictionary] mutableCopy]; 
    if (!iptc) 
    { 
     iptc = [NSMutableDictionary dictionaryWithCapacity:1]; 
    } 
    iptc[(NSString*)kCGImagePropertyIPTCCaptionAbstract] = @"Hardcoded Caption"; 
    metadataAsMutable[(NSString*)kCGImagePropertyIPTCDictionary] = iptc; 

    // log the new metadata as we want it written 
    NSLog(@"Parameter:\n------------------------------%@\n------------------------------", metadataAsMutable); 

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

    // create a new data object and write the new image into it 
    NSMutableData *dest_data = [NSMutableData data]; 
    CGImageDestinationRef destination = CGImageDestinationCreateWithData((__bridge CFMutableDataRef)dest_data,UTI,1,NULL); 
    if(!destination) 
    { 
     NSLog(@"Error: 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); 

    BOOL success = NO; 
    success = CGImageDestinationFinalize(destination); 
    if(!success) 
    { 
     NSLog(@"Error: Could not create data from image destination"); 
    } 

    // read and log post write metadata 
    CGImageSourceRef source2; 
    source2 = CGImageSourceCreateWithData((__bridge CFDataRef) dest_data, NULL); 
    NSDictionary *metadata2 = (NSDictionary *) CFBridgingRelease(CGImageSourceCopyPropertiesAtIndex(source2,0,NULL)); 
    NSLog(@"After:\n------------------------------%@\n------------------------------", metadata2); 

    // cleanup 
    CFRelease(destination); 

    // return the new data 
    return dest_data; 
} 

下面是當圖像具有現有值NSLogs關鍵：

Before: 
------------------------------{ 
    <...snip...> 
    "{IPTC}" =  { 
     "Caption/Abstract" = Blurry; 
     DateCreated = 20130923; 
     DigitalCreationDate = 20130923; 
     DigitalCreationTime = 173815; 
     Keywords =   (
      fake 
     ); 
     SupplementalCategory =   (
      fake 
     ); 
     TimeCreated = 173815; 
    }; 
    <...snip...> 
} 
------------------------------ 
Parameter: 
------------------------------{ 
    <...snip...> 
    "{IPTC}" =  { 
     "Caption/Abstract" = "Hardcoded Caption"; 
     DateCreated = 20130923; 
     DigitalCreationDate = 20130923; 
     DigitalCreationTime = 173815; 
     Keywords =   (
      fake 
     ); 
     SupplementalCategory =   (
      fake 
     ); 
     TimeCreated = 173815; 
    }; 
    <...snip...> 
} 
------------------------------ 
After: 
------------------------------{ 
    <...snip...> 
    "{IPTC}" =  { 
     "Caption/Abstract" = Blurry; 
     DateCreated = 20130923; 
     DigitalCreationDate = 20130923; 
     DigitalCreationTime = 173815; 
     Keywords =   (
      fake 
     ); 
     SupplementalCategory =   (
      fake 
     ); 
     TimeCreated = 173815; 
    }; 
    <...snip...> 
} 
------------------------------ 

這裏是NSLog的時候，圖像沒有鍵值：

Before: 
------------------------------{ 
    <...snip...> 
    "{IPTC}" =  { 
     DateCreated = 20130925; 
     DigitalCreationDate = 20130925; 
     DigitalCreationTime = 192856; 
     Keywords =   (
      fake 
     ); 
     SupplementalCategory =   (
      fake 
     ); 
     TimeCreated = 192856; 
    }; 
    <...snip...> 
} 
------------------------------ 
Parameter: 
------------------------------{ 
    <...snip...> 
    "{IPTC}" =  { 
     "Caption/Abstract" = "Hardcoded Caption"; 
     DateCreated = 20130925; 
     DigitalCreationDate = 20130925; 
     DigitalCreationTime = 192856; 
     Keywords =   (
      fake 
     ); 
     SupplementalCategory =   (
      fake 
     ); 
     TimeCreated = 192856; 
    }; 
    <...snip...> 
} 
------------------------------ 
After: 
------------------------------{ 
    <...snip...> 
    "{IPTC}" =  { 
     "Caption/Abstract" = "Hardcoded Caption"; 
     DateCreated = 20130925; 
     DigitalCreationDate = 20130925; 
     DigitalCreationTime = 192856; 
     Keywords =   (
      fake 
     ); 
     SupplementalCategory =   (
      fake 
     ); 
     TimeCreated = 192856; 
    }; 
    <...snip...> 
} 
------------------------------ 

Answer 1

根據IPTC文檔，description字段綁定到TIFF和EXIF地址。改變TIFF中的值也會更新IPTC條目！ 謝謝user2452250的提示。