CODEWITHSUNDEEP
c#.netimage-manipulationtiff
George Mauer
George Mauer

Reputation: 122202

How to modify tiff creation date in .Net

I am writing a pdf comparison utility. After some investigation it seems like the best way to do this is to convert to tiff and compare from there.

I managed to do this with Ghostscript but am getting a difference in the embedded creation date metadata.

different creation dates embedded in tiff

How do I use .Net to modify this?

Upvotes: 3

Views: 1006

Answers (4)

Daniel Frantik
Daniel Frantik

Reputation: 1

It seams that this ghostscript behavior could be supressed.

-dTIFFDateTime=false

https://www.ghostscript.com/doc/9.22/Devices.htm

... but for this situation I would recommend some diffpdf tools (http://soft.rubypdf.com/software/diffpdf)

D

Upvotes: 0

Nyerguds
Nyerguds

Reputation: 5639

If the date stamps are fixed size, a fun workaround for this type of problem is to write a FileStream which simply detects and blanks out such date stamps. In fact I've done this before for PDF comparison, on a project I worked on in school. The checksum comparison worked fine with just that, without any conversion to tiff, though in our specific case we were sure all compared PDFs were generated by the same system, so that simplified things a bit.

The basic method is to make a subclass of FileStream with overridden ReadByte and Read functions, which contains the length and expected format of the date stamps. Whenever a read is performed the following happens:

  • The code reads an extra piece, the size of the datestamp length minus 1 byte, both before and behind the requested data.
  • Inside that block, a search and replace is performed to clear any found date stamps.
  • Finally, the original requested piece is returned.

The source code I wrote for the project back in the day is here.

Upvotes: 0

wilsotc
wilsotc

Reputation: 800

After more investigation, it seems Microsoft does provide a TIFF library with multi-image support. It's in System.Windows.Media.Imaging. To get this namespace reference PresentationCore.

To access the TIFF metadata use this site as a reference: http://www.awaresystems.be/imaging/tiff/tifftags/baseline.html

This code accesses the date field after the GhostScript name you were interested in:

    FileInfo fi = new FileInfo(@"C:\Users\Chris\Downloads\PdfVerificationTests.can_use_image_approval_mode.approved.tiff");
    FileStream stream = fi.Open(FileMode.Open, FileAccess.ReadWrite,FileShare.None);
    TiffBitmapDecoder decoder = new TiffBitmapDecoder(stream, BitmapCreateOptions.None, BitmapCacheOption.OnLoad);
    BitmapMetadata bmd = (BitmapMetadata) decoder.Frames[0].Metadata;
    string thedateval = (string) bmd.GetQuery("/ifd/{ushort=306}");
    BitmapMetadata bmd2 = bmd.Clone();
    bmd2.SetQuery("/ifd/{ushort=306}", "2013:05:30 20:07:52");

This code does not write out a modified TIFF, but is all the info you need to do so. Hope this helps as I feel I'm beating a dead horse.

This code will strip all the attributes from a multipage TIFF and leave the image content intact:

    FileInfo fi = new FileInfo(@"C:\Users\Chris\Downloads\PdfVerificationTests.can_use_image_approval_mode.approved.tiff");
    FileStream stream = fi.Open(FileMode.Open, FileAccess.ReadWrite, FileShare.None);
    TiffBitmapDecoder decoder = new TiffBitmapDecoder(stream, BitmapCreateOptions.None, BitmapCacheOption.None);
    FileStream stream2 = new FileStream("empty.tif", FileMode.Create);
    TiffBitmapEncoder encoder = new TiffBitmapEncoder();
    for (int i = 0; i < decoder.Frames.Count(); i++)
    {
        BitmapSource source = decoder.Frames[i];
        int stride = source.PixelWidth * (source.Format.BitsPerPixel / 8);
        byte[] data = new byte[stride * source.PixelHeight];
        source.CopyPixels(data, stride, 0);
        CachedBitmap theSource = (CachedBitmap)BitmapSource.Create(source.PixelWidth, source.PixelHeight, source.DpiX, source.DpiY, source.Format, source.Palette, data, stride);
        encoder.Frames.Add(BitmapFrame.Create(theSource));
    }
    try
    {
        encoder.Save(stream2);
        stream2.Close();
        stream.Close();
    }
    catch
    {
    }

Upvotes: 1

Icemanind
Icemanind

Reputation: 48726

You can use LibTiff.NET. It is open source. Using this library, you can use the SetField method to modify any one of the many tags in the Tiff file, including the TiffTag.DATETIME flag.

Upvotes: 1

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