Tuesday, July 21, 2009

Remove Exif data from image files with C# and WPF libraries


(For my final solution check out Exif continued..)


A colleague of mine e-mailed me with a problem he had. He was developing a solution where the customer wanted all exif data to be removed from the images they provide on the web. He had tried a bit with no luck.

Since the image libraries in WPF is far superior to the ones in winforms I gave it a shot. I googled around, read the exif spec and came up with the code below. The image is read and then loop over all exif properties, and then blank them out. It might work just as good by removing them, but with blanking the file don’t change header wise. Properties pertaining to the image characteristics such as width and height are skipped. You can check them against the exif spec. I have only tried the code on jpeg images, and I didn’t have one with GPS coordinates in it, but in theory it should remove GPS coordinates as well.

I skipped the metadata.TrySave() all together since it didn’t work when I use the SetQuery method. If I just changed the metadata properties it worked. It’s easy to put this back in and you find a discussion about it in one of the links at the bottom.

using System;
using System.IO;
using System.Windows.Media.Imaging;

namespace ExifRemover
{
public class ExifReader
{
public void SetUpMetadataOnImage(string filename)
{
string tempName = Path.Combine(Path.GetDirectoryName(filename), Guid.NewGuid().ToString());
// open image file to read
using (Stream file = File.Open(filename, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
{
// create the decoder for the original file. The BitmapCreateOptions and BitmapCacheOption denote
// a lossless transocde. We want to preserve the pixels and cache it on load. Otherwise, we will lose
// quality or even not have the file ready when we save, resulting in 0b of data written
BitmapDecoder original = BitmapDecoder.Create(file, BitmapCreateOptions.PreservePixelFormat, BitmapCacheOption.None);
// create an encoder for the output file
BitmapEncoder output = null;
string ext = Path.GetExtension(filename);
switch (ext)
{
case ".png":
output = new PngBitmapEncoder();
break;
case ".jpg":
output = new JpegBitmapEncoder();
break;
case ".tif":
output = new TiffBitmapEncoder();
break;
}

if (original.Frames[0] != null && original.Frames[0].Metadata != null)
{
// So, we clone the object since it's frozen.
BitmapFrame frameCopy = (BitmapFrame)original.Frames[0].Clone();
BitmapMetadata metadata = original.Frames[0].Metadata.Clone() as BitmapMetadata;

StripMeta(metadata);

// finally, we create a new frame that has all of this new metadata, along with the data that was in the original message
output.Frames.Add(BitmapFrame.Create(frameCopy, frameCopy.Thumbnail, metadata, frameCopy.ColorContexts));
}
// finally, save the new file over the old file
using (Stream outputFile = File.Open(tempName, FileMode.Create, FileAccess.Write, FileShare.ReadWrite))
{
output.Save(outputFile);
}
}
File.Delete(filename);
File.Move(tempName, filename);
}

public void StripMeta(BitmapMetadata metaData)
{
for (int i = 270; i < 42016; i++)
{
if (i == 274 || i == 277 || i == 284 || i == 530 || i == 531 || i == 282 || i == 283 || i == 296) continue;

string query = "/app1/ifd/exif:{uint=" + i + "}";
BlankMetaInfo(query, metaData);

query = "/app1/ifd/exif/subifd:{uint=" + i + "}";
BlankMetaInfo(query, metaData);

query = "/ifd/exif:{uint=" + i + "}";
BlankMetaInfo(query, metaData);

query = "/ifd/exif/subifd:{uint=" + i + "}";
BlankMetaInfo(query, metaData);
}

for (int i = 0; i < 4; i++)
{
string query = "/app1/ifd/gps/{ulong=" + i + "}";
BlankMetaInfo(query, metaData);
query = "/ifd/gps/{ulong=" + i + "}";
BlankMetaInfo(query, metaData);
}
}

private void BlankMetaInfo(string query, BitmapMetadata metaData)
{
object obj = metaData.GetQuery(query);
if (obj != null)
{
if (obj is string)
metaData.SetQuery(query, string.Empty);
else
{
ulong dummy;
if (ulong.TryParse(obj.ToString(), out dummy))
{
metaData.SetQuery(query, 0);
}

}
}
}
}
}



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