NSData *imageData = UIImageJPEGRepresentation(image, 0.4);
CGImageSourceRef source = CGImageSourceCreateWithData((__bridge     CFDataRef)imageData, NULL);
NSMutableDictionary *metaDataDic = [self getEXIF:imageData];
NSMutableDictionary *exifDic = [[metaDataDic objectForKey:(NSString*)kCGImagePropertyExifDictionary] mutableCopy];
NSMutableDictionary *GPSDictionary = [[metaDataDic objectForKey:(NSString*)kCGImagePropertyGPSDictionary] mutableCopy];

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

NSTimeZone    *timeZone   = [NSTimeZone timeZoneForSecondsFromGMT:8*3600];
NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
[formatter setTimeZone:timeZone];
[formatter setDateFormat:@"YYYY:MM:dd hh:mm:ss"];
NSString *now = [formatter stringFromDate:[NSDate date]];
[exifDic setObject:now forKey:(NSString *)kCGImagePropertyExifDateTimeOriginal];

[metaDataDic setObject:exifDic forKey:(NSString*)kCGImagePropertyExifDictionary];

CFStringRef UTI = CGImageSourceGetType(source);
NSMutableData *newImageData = [NSMutableData data];
CGImageDestinationRef destination = CGImageDestinationCreateWithData((__bridge CFMutableDataRef)newImageData, UTI, 1, NULL);

CGImageDestinationAddImageFromSource(destination, source, 0, (__bridge CFDictionaryRef)metaDataDic);
CGImageDestinationFinalize(destination);

如果imageData初始值为69091bytes，添加Exif信息后会变成114691bytes，我并不想添加Exif信息后增加这么大的数据size，请问这是什么原因？