iphone - 如何将 exif 元数据写入图像(不是相机胶卷，只是 UIImage 或 JPEG)

Question

我知道如何使用 ALAssets 保存元数据。但是，我想保存图像，或将其上传到某个地方，并且 exif 完好无损。我将 exif 数据作为 NSDictionary。但是我怎样才能将它正确地注入(inject)到 UIImage(或者可能是 NSData JPEG 表示)中呢？

Answer 1

我正在使用 UIImagePickerController 从相机获取图像，我的流程与 Chiquis 所描述的略有不同。在这里:

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info {
    UIImage *image = info[@"UIImagePickerControllerOriginalImage"];
    NSString *fullPhotoFilename = ...; // generate the photo name and path here
    NSData *photoData = [UIImage taggedImageData:image.jpegData metadata:info[@"UIImagePickerControllerMediaMetadata"] orientation:image.imageOrientation];
    [photoData writeToFile:fullPhotoFilename atomically:YES];
}

并使用 UIImage 类别将图像数据与其元数据结合起来:

#import <ImageIO/ImageIO.h>
#import "UIImage+Tagging.h"
#import "LocationHelper.h"

@implementation UIImage (Tagging)

+ (NSData *)writeMetadataIntoImageData:(NSData *)imageData metadata:(NSMutableDictionary *)metadata {
    // create an imagesourceref
    CGImageSourceRef source = CGImageSourceCreateWithData((__bridge CFDataRef) imageData, NULL);

    // this is the type of image (e.g., public.jpeg)
    CFStringRef UTI = CGImageSourceGetType(source);

    // create a new data object and write the new image into it
    NSMutableData *dest_data = [NSMutableData data];
    CGImageDestinationRef destination = CGImageDestinationCreateWithData((__bridge CFMutableDataRef)dest_data, UTI, 1, NULL);
    if (!destination) {
        NSLog(@"Error: Could not create image destination");
    }
    // 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) metadata);
    BOOL success = NO;
    success = CGImageDestinationFinalize(destination);
    if (!success) {
        NSLog(@"Error: Could not create data from image destination");
    }
    CFRelease(destination);
    CFRelease(source);
    return dest_data;
}

+ (NSData *)taggedImageData:(NSData *)imageData metadata:(NSDictionary *)metadata orientation:(UIImageOrientation)orientation {
    CLLocationManager *locationManager = [CLLocationManager new];
    CLLocation *location = [locationManager location];
    NSMutableDictionary *newMetadata = [NSMutableDictionary dictionaryWithDictionary:metadata];
    if (!newMetadata[(NSString *)kCGImagePropertyGPSDictionary] && location) {
        newMetadata[(NSString *)kCGImagePropertyGPSDictionary] = [LocationHelper gpsDictionaryForLocation:location];
    }

    // Reference: http://sylvana.net/jpegcrop/exif_orientation.html
    int newOrientation;
    switch (orientation) {
        case UIImageOrientationUp:
            newOrientation = 1;
            break;

        case UIImageOrientationDown:
            newOrientation = 3;
            break;

        case UIImageOrientationLeft:
            newOrientation = 8;
            break;

        case UIImageOrientationRight:
            newOrientation = 6;
            break;

        case UIImageOrientationUpMirrored:
            newOrientation = 2;
            break;

        case UIImageOrientationDownMirrored:
            newOrientation = 4;
            break;

        case UIImageOrientationLeftMirrored:
            newOrientation = 5;
            break;

        case UIImageOrientationRightMirrored:
            newOrientation = 7;
            break;

        default:
            newOrientation = -1;
    }
    if (newOrientation != -1) {
        newMetadata[(NSString *)kCGImagePropertyOrientation] = @(newOrientation);
    }
    NSData *newImageData = [self writeMetadataIntoImageData:imageData metadata:newMetadata];
    return newImageData;
}

最后，这是我用来生成所需 GPS 字典的方法:

+ (NSDictionary *)gpsDictionaryForLocation:(CLLocation *)location {
    NSTimeZone      *timeZone   = [NSTimeZone timeZoneWithName:@"UTC"];
    NSDateFormatter *formatter  = [[NSDateFormatter alloc] init];
    [formatter setTimeZone:timeZone];
    [formatter setDateFormat:@"HH:mm:ss.SS"];

    NSDictionary *gpsDict = @{(NSString *)kCGImagePropertyGPSLatitude: @(fabs(location.coordinate.latitude)),
                          (NSString *)kCGImagePropertyGPSLatitudeRef: ((location.coordinate.latitude >= 0) ? @"N" : @"S"),
                          (NSString *)kCGImagePropertyGPSLongitude: @(fabs(location.coordinate.longitude)),
                          (NSString *)kCGImagePropertyGPSLongitudeRef: ((location.coordinate.longitude >= 0) ? @"E" : @"W"),
                          (NSString *)kCGImagePropertyGPSTimeStamp: [formatter stringFromDate:[location timestamp]],
                          (NSString *)kCGImagePropertyGPSAltitude: @(fabs(location.altitude)),
                          };
    return gpsDict;
}

希望对大家有帮助。感谢 Gustavo Ambrozio、Chiquis 和其他几个 SO 成员，我能够将它拼凑起来并在我的项目中使用它。