调整大小和设置JPEG图像的质量，同时在iOS中保留EXIF

Question

在iOS应用中，我有一个NSData对象，它是一个JPEG文件，需要将其调整为给定的分辨率（2048x2048），并且需要将JPEG质量设置为75％。需要在将EXIF数据保留在文件中的同时进行设置。该照片不在相机胶卷中-它是从DSLR相机通过网络拉出的，只是与应用程序临时存储在一起。如果图像通过UIImage行程，则EXIF数据将丢失。如何在不丢失EXIF的情况下执行调整大小和设置质量？还是有一种方法可以在转换前剥离EXIF数据，并在完成后将其添加回去？

Answer 1

您可以尝试CGImageSourceCreateThumbnailAtIndex和CGImageSourceCopyPropertiesAtIndex调整大小为jpeg图像的NSData对象的大小，而不会丢失EXIF。

我从问题设置图像的exif数据中得到启发

以下是我出于相同目的的代码。

干杯

+ (NSData *)JPEGRepresentationSavedMetadataWithImage:(NSData *)imageData compressionQuality:(CGFloat)compressionQuality maxSize:(CGFloat)maxSize
{
  CGImageSourceRef source = CGImageSourceCreateWithData((__bridge CFDataRef)imageData, NULL);

  CFDictionaryRef options = (__bridge CFDictionaryRef)@{(id)kCGImageSourceCreateThumbnailWithTransform: (id)kCFBooleanTrue,
                                                        (id)kCGImageSourceCreateThumbnailFromImageIfAbsent: (id)kCFBooleanTrue,
                                                        (id)kCGImageSourceThumbnailMaxPixelSize: [NSNumber numberWithDouble: maxSize], // The maximum width and height in pixels of a thumbnail
                                                        (id)kCGImageDestinationLossyCompressionQuality: [NSNumber numberWithDouble:compressionQuality]};
  CGImageRef thumbnail = CGImageSourceCreateThumbnailAtIndex(source, 0, options); // Create scaled image

  CFStringRef UTI = kUTTypeJPEG;
  NSMutableData *destData = [NSMutableData data];
  CGImageDestinationRef destination = CGImageDestinationCreateWithData((__bridge CFMutableDataRef)destData, UTI, 1, NULL);
  if (!destination) {
    NSLog(@"Failed to create image destination");
  }
  CGImageDestinationAddImage(destination, thumbnail, CGImageSourceCopyPropertiesAtIndex(source, 0, NULL)); // copy all metadata in source to destination
  if (!CGImageDestinationFinalize(destination)) {
    NSLog(@"Failed to create data from image destination");
  }

  CFRelease(destination);
  CFRelease(source);
  CFRelease(thumbnail);

  return [destData copy];
}