Question

在iOS应用中，我有一个NSData对象是一个JPEG文件，需要调整大小到给定的分辨率（2048x2048），并且需要将JPEG质量设置为75％。这些需要在保留文件中的EXIF数据的同时进行设置。照片不在相机胶卷中 - 它是通过网络从DSLR相机拉出来的，只是暂时与应用程序一起存储。如果图像通过UIImage进行，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？或者有没有办法在转换之前去除EXIF数据，并在完成后将其添加回来？

Answer 1

您可以尝试CGImageSourceCreateThumbnailAtIndex和CGImageSourceCopyPropertiesAtIndex来调整作为jpeg图像的NSData对象的大小而不会丢失EXIF。

我的灵感来自Problem setting exif data for an image

以下是我的代码用于相同的目的。

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];
}

Answer 2

Upvoted Greener Chen的答案，但这就是我在Swift 3中实现它的方式。几条评论：

我的函数接受一个jpeg缓冲区并返回一个jpeg缓冲区。它还会检查是否需要调整大小（检查源的最大维度），如果此处没有任何操作，则只返回输入缓冲区。您可能希望适应您的用例
我认为你不能将kCGImageDestinationLossyCompressionQuality之类的目标属性设置为CGImageSourceCreateThumbnailAtIndex() CGImageSource函数 - 但从未尝试过它。
请注意，通过将相关密钥（kCGImageDestinationLossyCompressionQuality）添加到保留的源元数据集中作为CGImageDestinationAddImage
的选项
，将压缩添加到目标图像

最初让我感到困惑的是，虽然我们正在为调整大小的目标图像提供完整的源图像元数据，CGImageDestinationAddImage()足够聪明，可以忽略源图像的任何维度数据（W + H）并使用正确的，已调整大小的图像，尺寸自动替换它。所以PixelHeight，PixelWidth（“根”元数据）＆amp; PixelXDimension＆amp; PixelYDimension（EXIF）不会从源传输，并且已正确设置为已调整大小的图像尺寸。

class func resizeImage(imageData: Data, maxResolution: Int, compression: CGFloat) -> Data? {

// create image source from jpeg data
if let myImageSource = CGImageSourceCreateWithData(imageData as CFData, nil) {

    // get source properties so we retain metadata (EXIF) for the downsized image
    if var metaData = CGImageSourceCopyPropertiesAtIndex(myImageSource,0, nil) as? [String:Any],
        let width = metaData[kCGImagePropertyPixelWidth as String] as? Int,
        let height = metaData[kCGImagePropertyPixelHeight as String] as? Int {

        let srcMaxResolution = max(width, height)

        // if max resolution is exceeded, then scale image to new resolution
        if srcMaxResolution >= maxResolution {
            let scaleOptions  = [ kCGImageSourceThumbnailMaxPixelSize as String : maxResolution,
                                  kCGImageSourceCreateThumbnailFromImageAlways as String : true] as [String : Any]

            if let scaledImage = CGImageSourceCreateThumbnailAtIndex(myImageSource, 0, scaleOptions as CFDictionary) {

                // add compression ratio to desitnation options
                metaData[kCGImageDestinationLossyCompressionQuality as String] = compression

                //create new jpeg
                let newImageData = NSMutableData()
                if let cgImageDestination = CGImageDestinationCreateWithData(newImageData, "public.jpeg" as CFString, 1, nil) {

                    CGImageDestinationAddImage(cgImageDestination, scaledImage, metaData as CFDictionary)
                    CGImageDestinationFinalize(cgImageDestination)

                    return newImageData as Data
                }

            }
        }
    }
}

return nil

}

Answer 3

我遇到了同样的问题，现在我可以使用EXIF数据上传文件，如果需要也可以压缩照片，这解决了我的问题：

// Get your image.
NSURL *url = @"http://somewebsite.com/path/to/some/image.jpg";
UIImage *loImgPhoto = [NSData dataWithContentsOfURL:url];

// Get your metadata (includes the EXIF data).
CGImageSourceRef loImageOriginalSource = CGImageSourceCreateWithData(( CFDataRef) loDataFotoOriginal, NULL);
NSDictionary *loDicMetadata = (__bridge NSDictionary *) CGImageSourceCopyPropertiesAtIndex(loImageOriginalSource, 0, NULL);

// Set your compression quality (0.0 to 1.0).
NSMutableDictionary *loDicMutableMetadata = [loDicMetadata mutableCopy];
[loDicMutableMetadata setObject:@(lfCompressionQualityValue) forKey:(__bridge NSString *)kCGImageDestinationLossyCompressionQuality];

// Create an image destination.
NSMutableData *loNewImageDataWithExif = [NSMutableData data];
CGImageDestinationRef loImgDestination = CGImageDestinationCreateWithData((__bridge CFMutableDataRef)loNewImageDataWithExif, CGImageSourceGetType(loImageOriginalSource), 1, NULL);


// Add your image to the destination.
CGImageDestinationAddImage(loImgDestination, loImgPhoto.CGImage, (__bridge CFDictionaryRef) loDicMutableMetadata);

// Finalize the destination.
if (CGImageDestinationFinalize(loImgDestination))
   {
       NSLog(@"Successful image creation.");                   
       // process the image rendering, adjustment data creation and finalize the asset edit.


       //Upload photo with EXIF metadata
       [self myUploadMethod:loNewImageDataWithExif];

    }
    else
    {
          NSLog(@"Error -> failed to finalize the image.");                         
    }

CFRelease(loImageOriginalSource);
CFRelease(loImgDestination);

Answer 4

您可以使用ExifTool之类的实用程序来删除和恢复EXIF。这是一个跨平台的命令行实用程序。以下是执行所需操作的相应命令。

删除EXIF：

exiftool -exif = image.jpg

在编辑图像后再次恢复EXIF：

exiftool -tagsfromfile image.jpg_original -exif image.jpg

在这个例子中，我利用了ExifTool自动生成的“_original”备份。

调整JPEG图像的大小和设置质量，同时在iOS中保留EXIF

4 个答案: