fix: write ExtraSamples Tiff tag when needed - #3614
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pomadchin
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July 11, 2026 21:48
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Thanks for the PR and sorry for the delay; will review shortly! |
pomadchin
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Jul 18, 2026
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LGTM! A solid improvement; I left a couple of comments; out of main gotchas
- ExtraSamplesTag is SHORTs
- We don't preserve the tag not on round trips (read + write with on actions in between), it might be a good idea to make it a part of the GeoTiffOptions
Let me know what you think / or I can help once have a bit of time!
| if (geoTiff.options.colorSpace == ColorSpace.RGB && geoTiff.options.rgbChannels > 3) { | ||
| bytes(0) = 2 // next band acts as alpha channel for RGB | ||
| } | ||
| fieldValues += TiffTagFieldValue(ExtraSamplesTag, BytesFieldType, extraBands, bytes) |
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I'm reading https://www.itu.int/itudoc/itu-t/com16/tiff-fx/docs/tiff6.pdf and it should be ShortsFieldType!
| if (extraBands > 0) { | ||
| val bytes = new Array[Byte](extraBands) | ||
| if (geoTiff.options.colorSpace == ColorSpace.RGB && geoTiff.options.rgbChannels > 3) { | ||
| bytes(0) = 2 // next band acts as alpha channel for RGB |
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- 0 - unspecified data
- 1 - associated alpha
- 2 - unassociated alpha
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| addToPurge(path) | ||
| val tiffTags = TiffTags.read(path) | ||
| val samples = tiffTags.nonBasicTags.extraSamples |
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our tiff does not preserve those 🤔 we could put it into options on read?
| addToPurge(path) | ||
| val tiffTags = TiffTags.read(path) | ||
| val samples = tiffTags.nonBasicTags.extraSamples | ||
| samples.get should equal(Array(0)) |
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^ "multi-tag.tif has 2 set for the extra samples tag
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| override def afterAll() = purge | ||
| override def afterAll() = { | ||
| println("done :)") |
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Overview
Adds the missing ExtraSamples Tiff tag when writing GeoTIFF files. Without this ExtraSamples tag the files are actually corrupt (but most tools are lenient enough to just give a warning and guess the correct values).
Checklist
Notes
Caveat : when writing RGB files with 4 bands, it is assumed that the 4th band is the alpha channel (RGBA).
Closes #3613