Incorrect ExifIfds for ImageHistory exif tag (or conversion issue from System.Drawing.Bitmap)

[JPDelprat]

Magick.NET version

14.14.0

Environment (Operating system, version and so on)

Windows 11

Description

When converting a System.Drawing.Bitmap into a MagickImage in Magick.NET, the EXIF tag ImageHistory (0x9213) is assigned a different ExifIfd compared to when the same image is loaded directly using Magick.NET.

Specifically:

When loading the image directly with new MagickImage("file.jpg"), the tag ImageHistory is assigned to ExifIfds.Exif.
When loading the image through System.Drawing.Bitmap and then converting it to MagickImage, the same tag is assigned to ExifIfds.Ifd0.

The tag value itself remains identical in both cases, but the ExifIfd differs depending on the input pipeline.

This inconsistency indicates that EXIF IFD assignment is not normalized across different loading paths. The Bitmap-based conversion path appears to lose or ignore original EXIF IFD grouping information, resulting in a fallback or default assignment to Ifd0.

As a result, metadata comparisons that include ExifIfd (for example equality checks between tags or profiles) will fail even though the underlying EXIF data is identical.

The issue is specific to the conversion pipeline involving System.Drawing.Bitmap and does not occur when images are loaded directly through Magick.NET.

Steps to Reproduce

Create a MagickImage.
Set the exif tag "ImageHistory" to a value.
Save to Test.jpg

=> Alternatively, you can use attached Test.jpg file, which contains some ImageHistory exif data.

Create a System.Drawing.Bitmap from this file.
Convert to MagickImage.

Call GetExifProfile().GetValue(ExifTag.ImageHistory) => you get null.
ImageHistory is present if exifProfile, with the correct tag value (0x9213) but ExifIfds set to "Ifd0" instead of expected "Exif"

Images

Test.jpg

[dlemstra]

This sounds like a bug in System.Drawing.Bitmap? I might be able to add a method on the ExifProfile that will move tags to the correct ifd. Would that help you?

[JPDelprat]

Hello,

Thanks for your answer.

If you are sure the correct Ifds for ImageHistory is "Exif", it is indeed a System.Drawing.Bitmap bug.
I haven't found some official source providing the correct value though.

This page is particular in not really clear :
https://exiv2.org/tags.html

"These are the Exif tags as defined in the Exif 2.3 standard.
IFD1 tags are not listed separately. All IFD0 tags may also be present in IFD1, according to the standard. The second part of the Exiv2 key of an IFD1 tag is Thumbnail (instead of Image), the other two parts of the key are the same as for IFD0 tags."

When comparing Tags, is it really needed to compare both value "ImageHistory" and Ifd ?
This is related to my previous remark (Ifd imposed or not for a given tag).

However, regarding ImageHistory, I've put a value of form "Text1,Text2,Text3", but on loading, System.Drawing.Bitmap truncates the value on at the first coma.

So the fix you propose (fix Ids when loading from System.Drawing.Bitmap) could help other people or me for other projects, but for current one, I've finally removed the System.Drawing.Bitmap transition (I now directly create ImageMagick from file).

So as you want... Fixing a bug is always interesting, but the bug is not in your code so....

Thanks