很多小伙伴浏览图片网站的时候，会发现图片的一些拍摄参数，包括光圈、像素、镜头、相机等，这些信息就是EXIF信息。
什么是EXIF
EXIF（Exchangeable Image File）是“可交换图像文件”的缩写，当中包含了专门为数码相机的照片而定制的元数据，可以记录数码照片的拍摄参数、缩略图及其他属性信息。Exif标准最初由日本电子工业发展协会（JEIDA - Japan Electronic Industry Development Association）制订，目前的最新版本是发布于2010年04月的 Exif 2.3 版，该版本曾在2012年12月以及2013年5月有所修正，并已经应用到各个厂商的新影像设备中。
简单来说，Exif 信息就是由数码相机在拍摄过程中采集一系列的信息，然后把信息放置在我们熟知的 JPEG/TIFF 文件的头部，也就是说 Exif信息是镶嵌在 JPEG/TIFF 图像文件格式内的一组拍摄参数，它就好像是傻瓜相机的日期打印功能一样，只不过 Exif信息所记录的资讯更为详尽和完备。Exif 所记录的元数据信息非常丰富，主要包含了以下几类信息：
- 拍摄日期
- 拍摄器材（机身、镜头、闪光灯等）
- 拍摄参数（快门速度、光圈F值、ISO速度、焦距、测光模式等）
- 图像处理参数（锐化、对比度、饱和度、白平衡等）
- 图像描述及版权信息
- GPS定位数据
- 缩略图
EXIF标签
iOS中如何取得图片的EXIF信息
要取得EXIF信息，首先要获取到图片的原始数据。iOS是通过UIImagePickerController这个类来获取图片的，下面我们就通过代码来说明。
- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
{
UIImage* tmpHeaderImg = [info objectForKey:UIImagePickerControllerEditedImage];
NSURL *fileUrl = [info objectForKey:UIImagePickerControllerImageURL];
//有的图片选择器返回的key是PHImageFileURLKey
CGImageSourceRef imageSource = CGImageSourceCreateWithURL((CFURLRef)fileUrl, NULL);
CFDictionaryRef imageInfo = CGImageSourceCopyPropertiesAtIndex(imageSource, 0,NULL);
//imageInfo 为图片全部EXIF信息
[self.image setImage:tmpHeaderImg];
}
代码写到这里用模拟器测试会发现，能获得图片的EXIF信息，但是一用真机运行就崩溃，这是为什么呢？
大家都知道，iOS上的APP只能取到沙盒里面的数据，而PHImageFileURLKey给出的地址是图片在手机里面的存储地址，APP是没有权限获取的。这时候我们就要用Asset来获取原始图片数据
[[PHImageManager defaultManager] requestImageDataForAsset:asset options:nil resultHandler:^(NSData * _Nullable imageData, NSString * _Nullable dataUTI, UIImageOrientation orientation, NSDictionary * _Nullable info) {
CGImageSourceRef imageSource = CGImageSourceCreateWithData((__bridge CFDataRef)imageData, NULL);
NSDictionary *imageInfo = (__bridge NSDictionary*)CGImageSourceCopyPropertiesAtIndex(imageSource, 0, NULL);
}];
通过Asset获取图片适用于真机和模拟器，这样想服务器上传上述方法返回的imageData，就可以获得含有EXIF信息的图片了。如果不获取图片原始数据直接从图片选择器上传图片，苹果或基于安全和隐私方面的考虑，会隐藏大部分的EXIF信息。
例
以下是上方图片的EXIF信息
Printing description of imageInfo:
{
ColorModel = RGB;
DPIHeight = 72;
DPIWidth = 72;
Depth = 8;
Orientation = 1;
PixelHeight = 3456;
PixelWidth = 5184;
ProfileName = "sRGB IEC61966-2.1";
"{ExifAux}" = {
AFInfo = (
"0.4895833",
"0.7025463",
"0.02083333",
"0.02488426",
n,
"0.3256173",
"0.598235",
"0.01697531",
"0.03096065",
n,
"0.6574074",
"0.598235",
"0.01697531",
"0.03096065",
n,
"0.2276234",
"0.4845197",
"0.01697531",
"0.03096065",
n,
"0.4875579",
"0.4810475",
"0.02488426",
"0.03790509",
F,
"0.7554013",
"0.4845197",
"0.01697531",
"0.03096065",
n,
"0.3256173",
"0.3708044",
"0.01697531",
"0.03096065",
n,
"0.6574074",
"0.3708044",
"0.01697531",
"0.03096065",
n,
"0.4895833",
"0.2725694",
"0.02083333",
"0.02488426",
n
);
Firmware = "Firmware Version 1.1.1";
FlashCompensation = 0;
FocusMode = 1;
ImageStabilization = 3;
LensID = 51;
LensInfo = (
18,
135,
0,
0,
18,
135,
0,
0
);
LensModel = "Canon EF-S 18-135mm f/3.5-5.6 IS";
SerialNumber = 331505805;
};
"{Exif}" = {
ApertureValue = 5;
BodySerialNumber = 0331505805;
ColorSpace = 1;
ComponentsConfiguration = (
1,
2,
3,
0
);
CustomRendered = 0;
DateTimeDigitized = "2017:04:04 10:09:52";
DateTimeOriginal = "2017:04:04 10:09:52";
ExifVersion = (
2,
3
);
ExposureBiasValue = 0;
ExposureMode = 0;
ExposureProgram = 3;
ExposureTime = "0.01";
FNumber = "5.6";
Flash = 16;
FlashPixVersion = (
1,
0
);
FocalLength = 135;
FocalPlaneResolutionUnit = 2;
FocalPlaneXResolution = "5728.176470588235";
FocalPlaneYResolution = "5808.403508771929";
ISOSpeedRatings = (
100
);
LensModel = "EF-S18-135mm f/3.5-5.6 IS";
LensSerialNumber = 000012e3b8;
LensSpecification = (
18,
135,
0,
0
);
MaxApertureValue = "5.656853725850966";
MeteringMode = 5;
PixelXDimension = 5184;
PixelYDimension = 3456;
RecommendedExposureIndex = 100;
SceneCaptureType = 0;
SensitivityType = 2;
ShutterSpeedValue = "6.625";
SubsecTime = 00;
SubsecTimeDigitized = 00;
SubsecTimeOriginal = 00;
WhiteBalance = 0;
};
"{IPTC}" = {
Byline = (
""
);
CopyrightNotice = "";
StarRating = 0;
};
"{MakerCanon}" = {
CameraTemperatur = 15;
ContinuousDrive = 0;
FocusDistanceLower = "1.66";
FocusDistanceUpper = "1.82";
LensModel = "EF-S18-135mm f/3.5-5.6 IS";
MaxAperture = "5.656854249492381";
MinAperture = "35.91878554589994";
UniqueModelID = 2147484295;
WhiteBalanceIndex = 0;
};
"{PictureStyle}" = {
ColorTone = (
0,
0,
0
);
Monochrome = (
0,
0,
0
);
PictStyleColorSpace = (
sRGB,
1,
1
);
PictureStyle = (
4095,
4095,
4095
);
SharpnessFreq = (
0,
0,
0
);
};
"{TIFF}" = {
Artist = "";
Copyright = "";
DateTime = "2017:04:04 10:09:52";
Make = Canon;
Model = "Canon EOS 60D";
Orientation = 1;
ResolutionUnit = 2;
XResolution = 72;
YResolution = 72;
};
}
如何修改图片的EXIF
- 获取图片中的EXIF文件
NSMutableDictionary *metaDataDic = [imageInfo mutableCopy];
NSMutableDictionary *exifDic =[[metaDataDic objectForKey:(NSString*)kCGImagePropertyExifDictionary]mutableCopy];
- 修改EXIF文件中的部分信息
[exifDic setObject:[NSNumber numberWithFloat:123123] forKey:(NSString *)kCGImagePropertyExifExposureTime];
[exifDic setObject:@"SenseTime" forKey:(NSString *)kCGImagePropertyExifLensModel];
[metaDataDic setObject:exifDic forKey:(NSString*)kCGImagePropertyExifDictionary];
- 将修改后的文件写入至图片中
CFStringRef UTI = CGImageSourceGetType(imageSource);
NSMutableData *newImageData = [NSMutableData data];
CGImageDestinationRef destination = CGImageDestinationCreateWithData((__bridge CFMutableDataRef)newImageData, UTI, 1,NULL);
//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)metaDataDic);
CGImageDestinationFinalize(destination)；
- 保存图片
NSString *directoryDocuments = NSTemporaryDirectory();
[newImageData writeToFile: directoryDocuments atomically:YES];
- 查看修改后图片的Exif信息
CIImage *testImage = [CIImage imageWithData:newImageData];
NSDictionary *propDict = [testImage properties];
NSLog(@"Properties %@", propDict);
注意事项
关于无法修改Exif值的几点注意事项：
- 传入的数据格式与Exif规定的不符
Exif的每条信息都有对应的数据类型，如：String Float... 如果数据类型传入错误将无法写入文件。- 传入的字段超过规定字段长度
- 相互依赖的字段只添加了一个字段
在GPS文件中经纬度的度数的字段与经纬度的方向的字段相互依赖，修改经／纬度数需要经／纬方向字段的存在，否则修改无效。
