Problem reading JPEG Metadata (Orientation)

问题

I've got a JPEG image which was taken on an iphone. On my desktop PC (Windows Photo Viewer, Google Chrome, etc) the orientation is incorrect.

I'm working on an ASP.NET MVC 3 web application where i need to upload photos (currently using plupload).

I've got some server-side code to process images, including reading EXIF data.

I've tried reading the PropertyTagOrientation field in the EXIF meta data (using GDI - Image.PropertyItems), but the field isn't present.

So it's either some specific iphone meta data, or some other meta data.

I've used another tool like Aurigma Photo Uploader, and it reads the meta data correctly and rotates the image. How does it do this?

Does anyone know what other JPEG meta data could contain the information required in order to know that it needs to be rotated, that is used by Aurigma?

Here's the code i'm using to read the EXIF data:

var image = Image.FromStream(fileStream);

foreach (var prop in image.PropertyItems)
{
   if (prop.Id == 112 || prop.Id == 5029)
   {
      // do my rotate code - e.g "RotateFlip"
      // Never get's in here - can't find these properties.
   }
}

Any ideas?

回答1:

It appears that you forgotten that the orientation id values you looked up are in hex. Where you use 112, you should have used 0x112.

This article explains how Windows ballsed-up orientation handing, and this one seems pretty relevant to what you are doing.

回答2:

Here is a snippet addressing the 8 orientation values.

First a few notes:

The EXIF id 0x0112 is for Orientation. This is a helpful EXIF id reference http://www.sno.phy.queensu.ca/~phil/exiftool/TagNames/EXIF.html

0x0112 is the hex equivalent of 274. The data type of a PropertyItem.Id is an int, meaning 274 is what is useful here.

Additionally, 5029 likely was supposed to be 0x5029 or 20521 which correlates to ThumbnailOrientation, though is likely not what is desired here.

Orient Image:

Note: img is a System.Drawing.Image or inherits from it, like System.Drawing.Bitmap.

if (Array.IndexOf(img.PropertyIdList, 274) > -1)
{
    var orientation = (int)img.GetPropertyItem(274).Value[0];
    switch (orientation)
    {
        case 1:
            // No rotation required.
            break;
        case 2:
            img.RotateFlip(RotateFlipType.RotateNoneFlipX);
            break;
        case 3:
            img.RotateFlip(RotateFlipType.Rotate180FlipNone);
            break;
        case 4:
            img.RotateFlip(RotateFlipType.Rotate180FlipX);
            break;
        case 5:
            img.RotateFlip(RotateFlipType.Rotate90FlipX);
            break;
        case 6:
            img.RotateFlip(RotateFlipType.Rotate90FlipNone);
            break;
        case 7:
            img.RotateFlip(RotateFlipType.Rotate270FlipX);
            break;
        case 8:
            img.RotateFlip(RotateFlipType.Rotate270FlipNone);
            break;
    }
    // This EXIF data is now invalid and should be removed.
    img.RemovePropertyItem(274);
}

回答3:

From this post looks like you need to check ID 274

foreach (PropertyItem p in properties) {
      if (p.Id == 274) {
            Orientation = (int)p.Value[0];
         if (Orientation == 6)
            oldImage.RotateFlip(RotateFlipType.Rotate90FlipNone);
         if (Orientation == 8)
            oldImage.RotateFlip(RotateFlipType.Rotate270FlipNone);
      break;
      }
}

回答4:

I combined the given answers and comments and came up this:

    MemoryStream stream = new MemoryStream(data);
    Image image = Image.FromStream(stream);

    foreach (var prop in image.PropertyItems) {
        if ((prop.Id == 0x0112 || prop.Id == 5029 || prop.Id == 274)) {
            var value = (int)prop.Value[0];
            if (value == 6) {
                image.RotateFlip(RotateFlipType.Rotate90FlipNone);
                break;
            } else if (value == 8) {
                image.RotateFlip(RotateFlipType.Rotate270FlipNone);
                break;
            } else if (value == 3) {
                image.RotateFlip(RotateFlipType.Rotate180FlipNone);
                break;
            } 
        }
    }

回答5:

Posting here just in case someone has the same issue. I had problems in production reading the orientation using WFP and GDI. The only thing that worked was using: https://github.com/dlemstra/Magick.NET

The code is fairly simple:

var img = new MagickImage(inputStream);
img.AutoOrient();   // Fix orientation
img.Strip();        // remove all EXIF information
img.Write(outputPath);

来源：https://stackoverflow.com/questions/6222053/problem-reading-jpeg-metadata-orientation