【Objc】将图片转为tiff存档

NSString *myPath = [[NSBundle mainBundle] pathForResource:@"IMG_2733" ofType:@"JPG"];
    NSURL *myURL = [NSURL fileURLWithPath:myPath];
    CGImageSourceRef mySourceRef = CGImageSourceCreateWithURL((CFURLRef)myURL, NULL);
    NSDictionary *myMetadata = (NSDictionary *) CGImageSourceCopyPropertiesAtIndex(mySourceRef,0,NULL);
    NSDictionary *exifDic = [myMetadata objectForKey:(NSString *)kCGImagePropertyExifDictionary];
    NSDictionary *tiffDic = [myMetadata objectForKey:(NSString *)kCGImagePropertyTIFFDictionary];
    NSLog(@"exifDic properties: %@", myMetadata); //all data
    float rawShutterSpeed = [[exifDic objectForKey:(NSString *)kCGImagePropertyExifExposureTime] floatValue];
    int decShutterSpeed = (1 / rawShutterSpeed);
    NSLog(@"Camera %@",[tiffDic objectForKey:(NSString *)kCGImagePropertyTIFFModel]);
    NSLog(@"Focal Length %@mm",[exifDic objectForKey:(NSString *)kCGImagePropertyExifFocalLength]);
    NSLog(@"Shutter Speed %@", [NSString stringWithFormat:@"1/%d", decShutterSpeed]);
    NSLog(@"Aperture f/%@",[exifDic objectForKey:(NSString *)kCGImagePropertyExifFNumber]);
    NSNumber *ExifISOSpeed  = [[exifDic objectForKey:(NSString*)kCGImagePropertyExifISOSpeedRatings] objectAtIndex:0];
    NSLog(@"ISO %i",[ExifISOSpeed integerValue]);
    NSLog(@"Taken %@",[exifDic objectForKey:(NSString*)kCGImagePropertyExifDateTimeDigitized]);