Problem reading JPEG Metadata (Orientation)

Question

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?

Answer 1

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);
}