GIMP 2.10.30 Multipage TIFF Reduced Image

Environment/Versions

• GIMP version: 2.10.30
• Package: Installer from gimp.org
• Operating System: Windows

Description of the bug

Open a TIFF that contains multiple images. Any image in the TIFF file that is tagged as FILETYPE_REDUCEDIMAGE is not available to view. The tiff code is assuming a FILETYPE_REDUCEDIMAGE tag value means the image is a thumbnail. That is an erroneous assumption. A reduced image may be a thumbnail but it may not be a thumbnail as well. Is there a way to disable this filtering? It is not apparent from the UI. If such as filter is necessary, there needs to be a way to disable it from the UI.

Reproduction

Is the bug reproducible? Always

Reproduction steps:

1. Open a TIFF that contains multiple images with some tagged as FILETYPE_REDUCEDIMAGE
2. A list of "pages" available in the TIFF are presented in a selection dialog.
3. Any image tagged as FILETYPE_REDUCEDIMAGE is omitted from the list and cannot be selected.

…

Expected result:

All images in the TIFF should be available for viewing.

Actual result:

Only a subset of the images in the TIFF are available.

Additional information

Nowhere in the TIFF Specification does it say that the reducedimage tag value means the image is a thumbnail.