Matt, Tiffinfo reports the following. Note the "Transparency Mask" subfile.
$ tiffinfo sample-no-mask.tif ... TIFF Directory at offset 0xe2 (226) Image Width: 304 Image Length: 285 Tile Width: 512 Tile Length: 512 Bits/Sample: 8 Sample Format: unsigned integer Compression Scheme: JPEG Photometric Interpretation: YCbCr YCbCr Subsampling: 2, 2 Samples/Pixel: 3 Planar Configuration: single image plane Reference Black/White: 0: 0 255 1: 128 255 2: 128 255 Tag 33550: 100.000000,100.000000,0.000000 Tag 33922: 0.000000,0.000000,0.000000,343739.586723,1091611.850704,0.000000 Tag 34735: 1,1,0,7,1024,0,1,1,1025,0,1,1,1026,34737,21,0,2049,34737,6,21,2054,0,1,9102,3072,0,1,3578,3076,0,1,9001 Tag 34737: NAD83 / Yukon Albers|NAD83| JPEG Tables: (142 bytes) TIFF Directory at offset 0x33a (826) Subfile Type: transparency mask (4 = 0x4) Image Width: 304 Image Length: 285 Tile Width: 512 Tile Length: 512 Bits/Sample: 1 Sample Format: unsigned integer Compression Scheme: AdobeDeflate Photometric Interpretation: transparency mask Samples/Pixel: 1 Planar Configuration: single image plane Predictor: none 1 (0x1) This is recognised by GDAL and treated as a special kind of mask as indicated in the gdalinfo report: $ gdalinfo sample-no-mask.tif Driver: GTiff/GeoTIFF Files: sample-no-mask.tif Size is 304, 285 ... Origin = (343739.586723418149631,1091611.850704099284485) Pixel Size = (100.000000000000000,-100.000000000000000) Metadata: AREA_OR_POINT=Area Image Structure Metadata: COMPRESSION=YCbCr JPEG INTERLEAVE=PIXEL SOURCE_COLOR_SPACE=YCbCr Corner Coordinates: Upper Left ( 343739.587, 1091611.851) Lower Left ( 343739.587, 1063111.851) Upper Right ( 374139.587, 1091611.851) Lower Right ( 374139.587, 1063111.851) Center ( 358939.587, 1077361.851) Band 1 Block=512x512 Type=Byte, ColorInterp=Red Mask Flags: PER_DATASET Band 2 Block=512x512 Type=Byte, ColorInterp=Green Mask Flags: PER_DATASET Band 3 Block=512x512 Type=Byte, ColorInterp=Blue Mask Flags: PER_DATASET In QGIS's "Information" tab under properties I see: "More Information: Mask band (exposed as alpha band)" So QGIS is using the special mask as alpha. I find that if I do: tiffcp sample-no-mask.tif,0 x0.tif I get an "x0.tif" with just the jpeg image, and not the mask. That may be helpful for you (without uncompressing the jpeg image). Best regards, Frank On Mon, Jan 17, 2022 at 7:38 PM <matt.wil...@yukon.ca> wrote: > I’m confused. The attached image has no Nodata, but when dropped into Qgis > and ArcGIS large areas are still drawn transparently, and there is no 4th > band for a mask or alpha. How is this happening? > > > > (I’m trying to get completely rid of all Nodata and Mask info, so as to > start over creating one of those from blank slate). > > > > *Matt Wilkie* > > Geomatics Developer & Administrator > > Environment | Technology, Innovation and Mapping > > T 867-667-8133 | *Yukon.ca <http://yukon.ca/>* > > *Hours: 08:30-16:30, Mon-Wed: Office, Thu: Remote, Fri: Away.* > > > _______________________________________________ > gdal-dev mailing list > gdal-dev@lists.osgeo.org > https://lists.osgeo.org/mailman/listinfo/gdal-dev > -- ---------------------------------------+-------------------------------------- I set the clouds in motion - turn up | Frank Warmerdam, warmer...@pobox.com light and sound - activate the windows | +1 650-701-7823 and watch the world go round - Rush | Geospatial Software Developer
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