最近有一个需求，要求用手机拍个照片，并切需要拍摄时间，拍摄gps，拍摄具体街道信息。
首先要感谢PhotoGPSdemo的作者，你可以到这里下载demo http://www.cocoachina.com/bbs/read.php?tid=130501。
以前，总认为jpg就是包含了像素信息的2进制文件，其实，jpg中还可以包含许多起它的信息，只不过我们平常用查看jpg属性时，系统没有给我们把信息全部显示出来而已！
在iOS中，提供了一组函数来操作jpg的这些额外的信息，你需要#import <ImageIO/ImageIO.h>才能使用他们。
首先，需要注意的是，UIImage对象中是没有这些信息的，它仅仅包含图像本身，jpg才包含这些信息，请不要弄混。
先看看怎么从jpg图片中取得各种额外信息，代码如下
- (IBAction)test { NSString * home = NSHomeDirectory(); NSData *data = [NSData dataWithContentsOfFile:[NSString stringWithFormat:@"%@/Documents/xx.jpg",home]]; CGImageSourceRef imgSource = CGImageSourceCreateWithData((__bridge CFDataRef)data, NULL); CFDictionaryRef metaDataDicRef = CGImageSourceCopyPropertiesAtIndex(imgSource,0,nil); NSLog(@"cfdictionary %@",(__bridge NSDictionary *)metaDataDicRef); NSDictionary *dic = (__bridge NSDictionary *)metaDataDicRef; NSDictionary *exifDic = [dic objectForKey:(NSString *)kCGImagePropertyExifDictionary]; NSString *location = [exifDic objectForKey:(NSString *)kCGImagePropertyExifCameraOwnerName]; NSLog(@"location is %@",location); NSString *DateTimeOriginal = [exifDic objectForKey:(NSString *)kCGImagePropertyExifDateTimeOriginal]; NSLog(@"time is %@",DateTimeOriginal); CFRelease(metaDataDicRef); CFRelease(imgSource); }
首先，需要用到CGImageSourceRef类，不能用UIImage类型(需要验证。。。)，这种CGImageSourceRef类型可以通过函数取出jpg的额外数据，这些数据叫做metaData，翻译过来就是元数据。得到的metaData是以字典形式返回的，其中的key是固定的，具体声明见下方
CFStringRef kCGImagePropertyTIFFDictionary;
CFStringRef kCGImagePropertyGIFDictionary;
CFStringRef kCGImagePropertyJFIFDictionary;
CFStringRef kCGImagePropertyExifDictionary;
CFStringRef kCGImagePropertyPNGDictionary;
CFStringRef kCGImagePropertyIPTCDictionary;
CFStringRef kCGImagePropertyGPSDictionary;
CFStringRef kCGImagePropertyRawDictionary;
CFStringRef kCGImagePropertyCIFFDictionary;
CFStringRef kCGImageProperty8BIMDictionary;
CFStringRef kCGImagePropertyDNGDictionary;
CFStringRef kCGImagePropertyExifAuxDictionary;
这些key中，有许多key对应的对象还是一个字典，比如kCGImagePropertyExifDictionary所对应的对象包含一下key值
const CFStringRef kCGImagePropertyExifExposureTime; const CFStringRef kCGImagePropertyExifFNumber; const CFStringRef kCGImagePropertyExifExposureProgram; const CFStringRef kCGImagePropertyExifSpectralSensitivity; const CFStringRef kCGImagePropertyExifISOSpeedRatings; const CFStringRef kCGImagePropertyExifOECF; const CFStringRef kCGImagePropertyExifVersion; const CFStringRef kCGImagePropertyExifDateTimeOriginal; const CFStringRef kCGImagePropertyExifDateTimeDigitized; const CFStringRef kCGImagePropertyExifComponentsConfiguration; const CFStringRef kCGImagePropertyExifCompressedBitsPerPixel; const CFStringRef kCGImagePropertyExifShutterSpeedValue; const CFStringRef kCGImagePropertyExifApertureValue; const CFStringRef kCGImagePropertyExifBrightnessValue; const CFStringRef kCGImagePropertyExifExposureBiasValue; const CFStringRef kCGImagePropertyExifMaxApertureValue; const CFStringRef kCGImagePropertyExifSubjectDistance; const CFStringRef kCGImagePropertyExifMeteringMode; const CFStringRef kCGImagePropertyExifLightSource; const CFStringRef kCGImagePropertyExifFlash; const CFStringRef kCGImagePropertyExifFocalLength; const CFStringRef kCGImagePropertyExifSubjectArea; const CFStringRef kCGImagePropertyExifMakerNote; const CFStringRef kCGImagePropertyExifUserComment; const CFStringRef kCGImagePropertyExifSubsecTime; const CFStringRef kCGImagePropertyExifSubsecTimeOrginal; const CFStringRef kCGImagePropertyExifSubsecTimeDigitized; const CFStringRef kCGImagePropertyExifFlashPixVersion; const CFStringRef kCGImagePropertyExifColorSpace; const CFStringRef kCGImagePropertyExifPixelXDimension; const CFStringRef kCGImagePropertyExifPixelYDimension; const CFStringRef kCGImagePropertyExifRelatedSoundFile; const CFStringRef kCGImagePropertyExifFlashEnergy; const CFStringRef kCGImagePropertyExifSpatialFrequencyResponse; const CFStringRef kCGImagePropertyExifFocalPlaneXResolution; const CFStringRef kCGImagePropertyExifFocalPlaneYResolution; const CFStringRef kCGImagePropertyExifFocalPlaneResolutionUnit; const CFStringRef kCGImagePropertyExifSubjectLocation; const CFStringRef kCGImagePropertyExifExposureIndex; const CFStringRef kCGImagePropertyExifSensingMethod; const CFStringRef kCGImagePropertyExifFileSource; const CFStringRef kCGImagePropertyExifSceneType; const CFStringRef kCGImagePropertyExifCFAPattern; const CFStringRef kCGImagePropertyExifCustomRendered; const CFStringRef kCGImagePropertyExifExposureMode; const CFStringRef kCGImagePropertyExifWhiteBalance; const CFStringRef kCGImagePropertyExifDigitalZoomRatio; const CFStringRef kCGImagePropertyExifFocalLenIn35mmFilm; const CFStringRef kCGImagePropertyExifSceneCaptureType; const CFStringRef kCGImagePropertyExifGainControl; const CFStringRef kCGImagePropertyExifContrast; const CFStringRef kCGImagePropertyExifSaturation; const CFStringRef kCGImagePropertyExifSharpness; const CFStringRef kCGImagePropertyExifDeviceSettingDescription; const CFStringRef kCGImagePropertyExifSubjectDistRange; const CFStringRef kCGImagePropertyExifImageUniqueID; const CFStringRef kCGImagePropertyExifGamma; const CFStringRef kCGImagePropertyExifCameraOwnerName; const CFStringRef kCGImagePropertyExifBodySerialNumber; const CFStringRef kCGImagePropertyExifLensSpecification; const CFStringRef kCGImagePropertyExifLensMake; const CFStringRef kCGImagePropertyExifLensModel; const CFStringRef kCGImagePropertyExifLensSerialNumber;
这里的每一个key都有具体的含义，代表了jpg的一些信息。这些key和key的值时有严格的格式限定的，你用了自己定义的key或者不符合规则的值，是不能正确地写入jpg文件的（待会要提到如何写入metaData信息）。
如何用UIImagePickerController拍摄照片后加入信息呢？用这个控件拍照后，默认生成的metaData信息较少，只有拍摄时间等几个信息，没有gps信息，更没有街道信息，我们需要手动加入。
#pragma mark - UIImagePickerControllerDelegate
- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
{
_mediaInfo =[NSMutableDictionarydictionaryWithDictionary:info];
if (!_locationManager) {
_locationManager = [[CLLocationManager alloc]init];
[_locationManagersetDelegate:self];
[_locationManagersetDistanceFilter:kCLDistanceFilterNone];
[_locationManagersetDesiredAccuracy:kCLLocationAccuracyBest];
}
[_locationManagerstartUpdatingLocation];
[picker dismissViewControllerAnimated:YEScompletion:^
{
}];
}
#pragma mark CLLocationManagerDelegate
- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation{
[manager stopUpdatingLocation];
UIImage *originalImage= (UIImage *) [_mediaInfoobjectForKey:UIImagePickerControllerOriginalImage];
NSData *imageNSData = UIImageJPEGRepresentation(originalImage,1);
CGImageSourceRef imgSource = CGImageSourceCreateWithData((__bridge CFDataRef)imageNSData, NULL);
//this is the type of image (e.g., public.jpeg)
CFStringRef UTI = CGImageSourceGetType(imgSource);
//this will be the data CGImageDestinationRef will write into
NSMutableData *newImageData = [NSMutableDatadata];
CGImageDestinationRef destination = CGImageDestinationCreateWithData((__bridge CFMutableDataRef)newImageData, UTI, 1, NULL);
if(!destination)
{
NSLog(@"***Could not create image destination ***");
return;
}
//get original metadata
NSDictionary *dict = [_mediaInfoobjectForKey:UIImagePickerControllerMediaMetadata];
NSMutableDictionary *metadata = [NSMutableDictionarydictionaryWithDictionary:dict];
//set gps info into metadata,we need a dictionary
NSDictionary * gpsDict=[newLocation GPSDictionary];
if (metadata && gpsDict) {
[metadata setValue:gpsDict forKey:(NSString*)kCGImagePropertyGPSDictionary];
}
//get location detail by CLGeocoder, this needs wifi
CLGeocoder *geocoder = [[CLGeocoder alloc] init];
[geocoder reverseGeocodeLocation:newLocation completionHandler:^(NSArray *placemarks, NSError *error){
if(error != nil)
{
NSLog(@"CLGeocoder error :%@ ",error);
}
else//if we can get place info ,we set it into meteData dic with kCGImagePropertyExifCameraOwnerName key
{
if(placemarks.count > 0)
{
CLPlacemark *placemark = [placemarks objectAtIndex:0];
NSMutableDictionary *eifDic = (NSMutableDictionary *)[metadata objectForKey:(NSString *)kCGImagePropertyExifDictionary];
[eifDic setObject:placemark.nameforKey:(NSString *)kCGImagePropertyExifCameraOwnerName];
}
}
//add the image contained in the image source to the destination, overidding the old metadata with our modified metadata
CGImageDestinationAddImageFromSource(destination, imgSource, 0, (__bridge CFDictionaryRef) metadata);
BOOL success = NO;
success = CGImageDestinationFinalize(destination);
if(!success) {
NSLog(@"***Could not create data from image destination ***");
return ;
}
CFRelease(imgSource);
CFRelease(destination);
[self sendData:newImageData];
[self writeTest:newImageData];
}];
}
@implementation CLLocation (GPSDictionary)
-(NSDictionary*)GPSDictionary{
NSDateFormatter *formatter = [[NSDateFormatteralloc] init];
[formatter setDateFormat:@"hh:mm:ss.SS"];
CLLocation *location=self;
NSDictionary *gpsDict = [NSDictionarydictionaryWithObjectsAndKeys:
[NSNumbernumberWithFloat:fabs(location.coordinate.latitude)], kCGImagePropertyGPSLatitude,
((location.coordinate.latitude >= 0) ? @"N" : @"S"), kCGImagePropertyGPSLatitudeRef,
[NSNumbernumberWithFloat:fabs(location.coordinate.longitude)], kCGImagePropertyGPSLongitude,
((location.coordinate.longitude >= 0) ? @"E" : @"W"), kCGImagePropertyGPSLongitudeRef,
[formatter stringFromDate:[location timestamp]], kCGImagePropertyGPSTimeStamp,
nil];
NSLog(@"gpsDict i %@",gpsDict);
return gpsDict;
}
@end
上面代码需要手动改改，它的最终目的就是用 CGImageDestinationAddImageFromSource(destination, imgSource, 0, (__bridge CFDictionaryRef) metadata);函数用新的metaData信息生成新的jpg数据。
其中gps数据用了系统自定义的key值写入，街道信息没有找到合适的key，就冒用了kCGImagePropertyExifCameraOwnerName这个key。