convert from CGImageMetadata to nsdictionary - ios

Question

i tried to convert my 360° metadata image to nsdictionary. every time the app crash when i tried to print a value for an attribute. i wrote this code
CGImageSourceRef source = CGImageSourceCreateWithData((__bridge CFDataRef)imageData, NULL);
NSArray *metadataArray = nil;
if (source) {
_metaData = CGImageSourceCopyMetadataAtIndex(source, 0, NULL);
if (_metaData) {
metadataArray = CFBridgingRelease(CGImageMetadataCopyTags(_metaData));
CFRelease(_metaData);
}
CFRelease(source);
}
NSLog(#"%#",metadataArray[12]);//this is the problem
In the output, i find that the type of immutableMetadata is CGImageMetadata not a NSdictionary. How i can convert to nsdictionary please??

Answer 1

Swift
extension CGImageSource {
func metadata() -> Dictionary<String, Any>? {
guard let imageMetadata = CGImageSourceCopyMetadataAtIndex(self, 0, .none) else {
return .none
}
guard let tags = CGImageMetadataCopyTags(imageMetadata) else {
return .none
}
var result = [String: Any]()
for tag in tags as NSArray {
let tagMetadata = tag as! CGImageMetadataTag
if let cfName = CGImageMetadataTagCopyName(tagMetadata) {
let name = String(cfName)
let value = CGImageMetadataTagCopyValue(tagMetadata)
result[name] = value
}
}
return result
}
}

Answer 2

I don't know much about ImageIO. It's full of CF/CG stuff, which may lead to __bridge uses.
You are only interested in a value, but if someone is looking for another, it could use that sample code/research:
I looked into CGImageMetadata.h for each use of functions related to CGImageMetadataTagRef that may be useful.
CGImageSourceRef source = CGImageSourceCreateWithData((CFDataRef)imagedata, NULL);
CGImageMetadataRef imageMetadataRef = CGImageSourceCopyMetadataAtIndex(source, 0, NULL);
NSArray *metadata = CFBridgingRelease(CGImageMetadataCopyTags(imageMetadataRef));
NSLog(#"metadata = %#", metadata);
for (id aRef in metadata)
{
CGImageMetadataTagRef currentRef = (__bridge CGImageMetadataTagRef)(aRef);
NSLog(#"Ref: %#", currentRef);
CGImageMetadataType type = CGImageMetadataTagGetType(currentRef);
NSLog(#"Type: %d", type);
CFStringRef nameSpace = CGImageMetadataTagCopyNamespace(currentRef);
NSLog(#"NameSpace: %#", nameSpace);
CFStringRef prefix = CGImageMetadataTagCopyPrefix(currentRef);
NSLog(#"prefix: %#", prefix);
CFStringRef name = CGImageMetadataTagCopyName(currentRef);
NSLog(#"name: %#", name);
CFTypeRef value = CGImageMetadataTagCopyValue(currentRef);
NSLog(#"Value: %#", value);
CFStringRef valueTypeStr = CFCopyTypeIDDescription(CFGetTypeID(value));
NSLog(#"valueTypeStr: %#", valueTypeStr);
//Test related to question
if ([#"GPano" isEqualToString:(__bridge NSString *)prefix] && [#"PoseHeadingDegrees" isEqualToString:(__bridge NSString *)name])
{
NSString *str = (__bridge NSString *)value;
NSLog(#"Str: %#", str);
NSLog(#"Int: %d", [str intValue]);
}
}
To know if the value is convertible to a more "known" object, like NSString (<=> CFString), NSArray (<=> CFArray), NSDictionary (<=> CFDictionary), I looked at CFStringRef valueTypeStr = CFCopyTypeIDDescription(CFGetTypeID(value)); (or you can also do a "quicker test" with related question: Determining what a CFTypeRef is?).
It's all "manually" done, I'm quite surprised that there is no conversion from CGImageMetadataTagRef to a more "known" object (and not struct), maybe there is, I didn't read the whole headers of CGImageMetadata.h, so there may be a quicker way, but I thought that even using "old school" approach, by digging could be useful for another user with a related question, helping him/her to find quickly what's he/she is looking for.
To answer your initial question: CGImageMetadata to NSDictionary, if there is no "easy conversion" tool, and with the "digging" approach, it's won't make a lot of sense, because the interesting method CGImageMetadataCopyTags returns a NSArray (or CFArray).
But since a lot of CGImageMetadataTagRef prefix are the same, you may be interested, by doing manually the following dictionary:
#{prefix1:#[stuff10, stuff11, etc.], prefix2:#[stuff20, stuff21, etc.]}