你如何覆盖图像元数据？
如果key / val已经存在于CGImageDestination的原始图像元数据中，我似乎无法正确地将图像元数据写入图像。 如果它们的key / val不存在于原始元数据中，它就可以正常工作。
几乎就像原始图像中的图像元数据属性优先于修改一样。 这是我不知道的某种拜占庭格式问题，我需要以某种不寻常的方式填充键/ val，一个bug，还是？ 有人看过这个吗？
下面的代码和输出，适用于它正常工作的两种情况（如果值尚未设置）并且无法写入（如果该值已设置为其他值）。
任何帮助表示非常感谢。
这是我在哪里/如何创建图像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]; 以下是元数据的实际修改：
- (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 (eg, 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; }
以下是图像具有密钥现有值时的NSLog：
Before: ------------------------------{ "{IPTC}" = { "Caption/Abstract" = Blurry; DateCreated = 20130923; DigitalCreationDate = 20130923; DigitalCreationTime = 173815; Keywords = ( fake ); SupplementalCategory = ( fake ); TimeCreated = 173815; }; } ------------------------------ Parameter: ------------------------------{ "{IPTC}" = { "Caption/Abstract" = "Hardcoded Caption"; DateCreated = 20130923; DigitalCreationDate = 20130923; DigitalCreationTime = 173815; Keywords = ( fake ); SupplementalCategory = ( fake ); TimeCreated = 173815; }; } ------------------------------ After: ------------------------------{ "{IPTC}" = { "Caption/Abstract" = Blurry; DateCreated = 20130923; DigitalCreationDate = 20130923; DigitalCreationTime = 173815; Keywords = ( fake ); SupplementalCategory = ( fake ); TimeCreated = 173815; }; } ------------------------------
以下是图像没有键值的NSLog：
Before: ------------------------------{ "{IPTC}" = { DateCreated = 20130925; DigitalCreationDate = 20130925; DigitalCreationTime = 192856; Keywords = ( fake ); SupplementalCategory = ( fake ); TimeCreated = 192856; }; } ------------------------------ Parameter: ------------------------------{ "{IPTC}" = { "Caption/Abstract" = "Hardcoded Caption"; DateCreated = 20130925; DigitalCreationDate = 20130925; DigitalCreationTime = 192856; Keywords = ( fake ); SupplementalCategory = ( fake ); TimeCreated = 192856; }; } ------------------------------ After: ------------------------------{ "{IPTC}" = { "Caption/Abstract" = "Hardcoded Caption"; DateCreated = 20130925; DigitalCreationDate = 20130925; DigitalCreationTime = 192856; Keywords = ( fake ); SupplementalCategory = ( fake ); TimeCreated = 192856; }; } ------------------------------
根据IPTC文档，描述字段绑定到TIFF和EXIF地址。 更改TIFF中的值也会更新IPTC条目！ 谢谢user2452250的提示。