libpano13 writes TIFF files with an alpha channel, but without the required
ExtraSamples
<https://www.awaresystems.be/imaging/tiff/tifftags/extrasamples.html> TIFF
metadata tag indicating that the 4th channel is alpha.
With the incorrect metadata, applications based on libtiff (e.g. tiffinfo)
print a warning when opening a file created by PTUncrop:
TIFFReadDirectory: Warning, Sum of Photometric type-related color channels
and ExtraSamples doesn't match SamplesPerPixel. Defining non-color channels
as ExtraSamples..
Pillow 9.1.0 (Python library) fails to load these images
<https://github.com/python-pillow/Pillow/issues/6266>, though this has been
fixed.
I couldn't figure out where libpano13's authoritative source repository is,
or how to submit a pull request or equivalent, so I've attached the patch
against libpano13 v2.9.21 here.
--
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http://wiki.panotools.org/Hugin_FAQ
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diff --git a/tiff.c b/tiff.c
index 218069b..c4baa01 100644
--- a/tiff.c
+++ b/tiff.c
@@ -385,6 +385,7 @@ int writeCroppedTIFF(Image * im, fullPath * sfile, CropInfo * crop_info)
case 32:
TIFFSetField(tif, TIFFTAG_BITSPERSAMPLE, 8);
TIFFSetField(tif, TIFFTAG_SAMPLESPERPIXEL, 4);
+ TIFFSetField(tif, TIFFTAG_EXTRASAMPLES, 1, &(uint16_t){EXTRASAMPLE_UNASSALPHA});
break;
case 48:
TIFFSetField(tif, TIFFTAG_BITSPERSAMPLE, 16);
@@ -393,6 +394,7 @@ int writeCroppedTIFF(Image * im, fullPath * sfile, CropInfo * crop_info)
case 64:
TIFFSetField(tif, TIFFTAG_BITSPERSAMPLE, 16);
TIFFSetField(tif, TIFFTAG_SAMPLESPERPIXEL, 4);
+ TIFFSetField(tif, TIFFTAG_EXTRASAMPLES, 1, &(uint16_t){EXTRASAMPLE_UNASSALPHA});
break;
case 96:
TIFFSetField(tif, TIFFTAG_BITSPERSAMPLE, 32);
@@ -402,6 +404,7 @@ int writeCroppedTIFF(Image * im, fullPath * sfile, CropInfo * crop_info)
case 128:
TIFFSetField(tif, TIFFTAG_BITSPERSAMPLE, 32);
TIFFSetField(tif, TIFFTAG_SAMPLESPERPIXEL, 4);
+ TIFFSetField(tif, TIFFTAG_EXTRASAMPLES, 1, &(uint16_t){EXTRASAMPLE_UNASSALPHA});
TIFFSetField(tif, TIFFTAG_SAMPLEFORMAT, SAMPLEFORMAT_IEEEFP);
break;
}
@@ -1077,6 +1080,9 @@ int panoTiffSetImageProperties(pano_Tiff * file)
metadata->imageTotalNumber);
+ if (returnValue && metadata->samplesPerPixel == 4) {
+ returnValue = TIFFSetField(tiffFile, TIFFTAG_EXTRASAMPLES, 1, &(uint16_t){EXTRASAMPLE_UNASSALPHA});
+ }
if (returnValue && metadata->bitsPerSample == 32)
