ExifTag.TimeZoneOffset is defined as uint[], but the TIFF spec defines it as signed short

[rwg0]

Prerequisites

• I have written a descriptive issue title
• I have verified that I am running the latest version of ImageSharp
• I have verified if the problem exist in both DEBUG and RELEASE mode
• I have searched open and closed issues to ensure it has not already been reported

ImageSharp version

3.0.1

Other ImageSharp packages and versions

?

Environment (Operating system, version and so on)

Windows 10 x64

.NET Framework version

.NET 7

Description

The TimeZoneOffset Exif tag is defined in the code as a uint[] (

ImageSharp/src/ImageSharp/Metadata/Profiles/Exif/Tags/ExifTag.LongArray.cs

Line 62 in a49862a

public static ExifTag<uint[]> TimeZoneOffset { get; } = new ExifTag<uint[]>(ExifTagValue.TimeZoneOffset);

)

However, the specifications for TIFF/EP which defines that tag seem to require a signed short (optionally two signed shorts). See Page 19 and 40 of the TIFF/EP spec : https://web.archive.org/web/20060212163025/http://www.map.tu.chiba-u.ac.jp/IEC/100/TA2/recdoc/N4378.pdf

This requirement is also encoded in the TIFF verification code in JHove, which then flags the file as non-conformant (https://jhove.openpreservation.org/modules/tiff/tags/ , https://jhove.openpreservation.org/)

As a side note, since ExifTag doesn't have a public constructor, I cannot create my own tags to work around this issue (or to add custom tags to the file).

Steps to Reproduce

Set the DateTimeOffsetTag in a tiff file, then save the file

var image = Image.Load(sourceTifFile);
image.Frames[0].Metadata.ExifProfile = new ExifProfile();
image.Frames[0].Metadata.ExifProfile.SetValue(ExifTag.TimeZoneOffset, new uint[] {1});
image.Save(outputTifFile);

Now run the output tiff file through jhove verification

robin@ubuntu:~$ jhove -m TIFF-hul Output.tif 
Jhove (Rel. 1.20.0, 2019-01-19)
 Date: 2023-04-13 13:33:05 PDT
 RepresentationInformation: Output.tif
  ReportingModule: TIFF-hul, Rel. 1.8 (2017-05-11)
  LastModified: 2023-04-13 13:27:13 PDT
  Size: 343128
  Format: TIFF
  Status: Not well-formed
  SignatureMatches:
   TIFF-hul
  ErrorMessage: Type mismatch for tag 34858; expecting 8, saw 4
  MIMEtype: image/tiff

You can install jhove on an ubuntu box with

sudo apt-get install jhove default-jre

Note: I ran the ImageSharp test code on Windows, just used Ubuntu for testing as the jhove install is easier

Images

No response

[dlemstra]

That looks like a mistake indeed but changing this would introduce a breaking change. But I do wonder if anyone is using this since we implemented this incorrectly. Maybe we could patch this in a minor release and make a note about this minor breaking change in the release notes?

[rwg0]

To avoid a breaking change you could attribute the existing TimeZoneOffset property as [Obsolete] and add a new property with the correct definition.

[JimBobSquarePants]

While it affects the public API I don’t consider bug fixes like this to require minor versions. I’d be happy shipping a fix without one.

[JimBobSquarePants]

I'm happy for this to be fixed in v3.1