Fix small deviation to the spec when encoding tiff images

[brianpopow]

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Description

This PR fixes the following issues when encoding tiff images:

• Write padding byte, because the tiff spec requires ifd offset to begin on a word boundary.
• Change samples per pixel to ushort

Closes #2297

[JimBobSquarePants]

LGTM 👍

[brianpopow]

There is a failing test, I am trying to figure out if it is a regression introduced with this changes, but I dont know how yet.

[JimBobSquarePants]

I’ll have a poke at it later.

[JimBobSquarePants]

@brianpopow There appears to be a corrupted EXIF value in the encoded output. Unknown tag of type byte[] with two entries at the beginning with the rest empty.

[brianpopow]

The input image metadata_sample.tiff already seems to be completely broken:

identify: Unknown field with tag 18246 (0x4746) encountered. `TIFFReadDirectory' @ warning/tiff.c/TIFFWarnings/950.
identify: Unknown field with tag 18249 (0x4749) encountered. `TIFFReadDirectory' @ warning/tiff.c/TIFFWarnings/950.
identify: Unknown field with tag 40091 (0x9c9b) encountered. `TIFFReadDirectory' @ warning/tiff.c/TIFFWarnings/950.
identify: Unknown field with tag 40092 (0x9c9c) encountered. `TIFFReadDirectory' @ warning/tiff.c/TIFFWarnings/950.
identify: Unknown field with tag 40093 (0x9c9d) encountered. `TIFFReadDirectory' @ warning/tiff.c/TIFFWarnings/950.
identify: Unknown field with tag 40094 (0x9c9e) encountered. `TIFFReadDirectory' @ warning/tiff.c/TIFFWarnings/950.
identify: Unknown field with tag 40095 (0x9c9f) encountered. `TIFFReadDirectory' @ warning/tiff.c/TIFFWarnings/950.
identify: Unknown field with tag 59932 (0xea1c) encountered. `TIFFReadDirectory' @ warning/tiff.c/TIFFWarnings/950.
identify: IO error during reading of "Tag 40095"; tag ignored. `TIFFFetchNormalTag' @ warning/tiff.c/TIFFWarnings/950.
identify: F:\vsprojekte\ImageSharp.Playground\tests\Images\Input\Tiff\metadata_sample.tiff: Can not read TIFF directory. `TIFFFetchDirectory' @ error/tiff.c/TIFFErrors/597.
identify: Failed to read custom directory at offset 5596. `TIFFReadCustomDirectory' @ error/tiff.c/TIFFErrors/597.
identify: Unknown field with tag 18246 (0x4746) encountered. `TIFFReadDirectory' @ warning/tiff.c/TIFFWarnings/950.
identify: Unknown field with tag 18249 (0x4749) encountered. `TIFFReadDirectory' @ warning/tiff.c/TIFFWarnings/950.
identify: Unknown field with tag 40091 (0x9c9b) encountered. `TIFFReadDirectory' @ warning/tiff.c/TIFFWarnings/950.
identify: Unknown field with tag 40092 (0x9c9c) encountered. `TIFFReadDirectory' @ warning/tiff.c/TIFFWarnings/950.
identify: Unknown field with tag 40093 (0x9c9d) encountered. `TIFFReadDirectory' @ warning/tiff.c/TIFFWarnings/950.
identify: Unknown field with tag 40094 (0x9c9e) encountered. `TIFFReadDirectory' @ warning/tiff.c/TIFFWarnings/950.
identify: Unknown field with tag 40095 (0x9c9f) encountered. `TIFFReadDirectory' @ warning/tiff.c/TIFFWarnings/950.
identify: Unknown field with tag 59932 (0xea1c) encountered. `TIFFReadDirectory' @ warning/tiff.c/TIFFWarnings/950.
identify: IO error during reading of "Tag 40095"; tag ignored. `TIFFFetchNormalTag' @ warning/tiff.c/TIFFWarnings/950.

I will try to fix that first.

[brianpopow]

Ok the input file is fixed now. I assume the error in the encoded EXIF profile came from the corrupted input file.