Lossy mask band causes artifacts

[zdila]

What is the bug?

VRT file produces transparent pixels on mask edge.

Steps to reproduce the issue

Please download input data (54MB) from https://drive.google.com/file/d/1BgUZ2snzYeK3_7EpN4YCIZHe6niaywyJ/view?usp=sharing and unpack it. It contains one orthophoto image (SNINA_3-0.tif) and two overlapping masks (mask-left.tif and mask-right.tif).

1. create 2 vrt files:

   gdalbuildvrt -a_srs EPSG:8353 left.vrt SNINA_3-0.tif
   gdalbuildvrt -a_srs EPSG:8353 right.vrt SNINA_3-0.tif

2. edit left.vrt and right.vrt and add:

   <MaskBand>
     <VRTRasterBand dataType="Byte">
       <SimpleSource>
         <SourceFilename relativeToVRT="1">mask-left.tif</SourceFilename>
         <SourceBand>1</SourceBand>
       </SimpleSource>
     </VRTRasterBand>
   </MaskBand>

   (use mask-left.tif for left.vrt and mask-right.tif for right.vrt)

3. warp left and right:

   gdalwarp -s_srs 'EPSG:8353' -t_srs 'EPSG:3857' -tr 0.29858214173896972948 0.29858214173896972948 -tap -r lanczos -of GTiff -co COMPRESS=JXL -co JXL_DISTANCE=1 -co JXL_LOSSLESS=NO -dstalpha left.vrt left.tif
   gdalwarp -s_srs 'EPSG:8353' -t_srs 'EPSG:3857' -tr 0.29858214173896972948 0.29858214173896972948 -tap -r lanczos -of GTiff -co COMPRESS=JXL -co JXL_DISTANCE=1 -co JXL_LOSSLESS=NO -dstalpha right.vrt right.tif

4. produce final VRT:

   gdalbuildvrt final.vrt left.tif right.tif

Issue is not reproducible if JXL_LOSSLESS=YES (but I want it to be lossy because of the size).

Versions and provenance

Linux bono 6.11.7-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.11.7-1 (2024-11-09) x86_64 GNU/Linux

GDAL 3.11.0dev-051a853584, released 2024/10/31

Additional context

I have multiple huge jpeg-compressed geotiff orthophoto files which I want to reproject to pseudomercator and create a single VRT file from them. Each file covers a part of the country and they have some small overlap. For every JPEG I also have a cutline (vector mask) which I rasterize and use, because JPEG files have no alpha channel or mask.

I expect the resulting VRT to render without any gaps between parts.

I am using JXL because JPEG can't have an alpha channel.

[rouault]

maybe try -co JXL_ALPHA_DISTANCE=0 so the alpha channel is saved as lossless

[zdila]

@rouault this works for me. Thanks! Feel free to close this issue if it is actually not a bug.

Note that I was also trying to use alpha channel not as a mask, but as a classic alpha channel, but I also did not succeed.

Offtopic, feel free to ignore: it is possible to achieve the same with classic JPEG compression and with some external mask - all with overview support per a part (using gdaladdo)?

[rouault]

Note that I was also trying to use alpha channel not as a mask, but as a classic alpha channel, but I also did not succeed.

not sure to understand the difference between both

: it is possible to achieve the same with classic JPEG compression and with some external mask - all with overview support per a part (using gdaladdo)?

gdal_translate rgba.tif rgb_mask.tif -b 1 -b 2 -b 3 -mask 4 -co COMPRESS=JPEG [-co PHOTOMETRIC=YCBCR]

will generate a file with RGB JPEG compressed and an internal TIFF mask using lossless 1-bit Deflate lossless compression. You can use gdaladdo to add overviews to both RGB and mask channels

[zdila]

I've tried to use JPEG codec with internal tiff mask. First I replaced mask in my vrt files with alpha channels:

<VRTRasterBand dataType="Byte" band="4">
    <ColorInterp>Alpha</ColorInterp>
    <SimpleSource>
      <SourceFilename relativeToVRT="1">mask-left.tif</SourceFilename>
      <SourceBand>1</SourceBand>
    </SimpleSource>
  </VRTRasterBand>

Then:

gdalwarp -s_srs 'EPSG:8353' -t_srs 'EPSG:3857' -tr 0.29858214173896972948 0.29858214173896972948 -tap -r lanczos -of GTiff -co COMPRESS=ZSTD -b 1 -b 2 -b 3 -dstalpha right.vrt right-tmp.tif
gdalwarp -s_srs 'EPSG:8353' -t_srs 'EPSG:3857' -tr 0.29858214173896972948 0.29858214173896972948 -tap -r lanczos -of GTiff -co COMPRESS=ZSTD -b 1 -b 2 -b 3 -dstalpha left.vrt left-tmp.tif

gdal_translate left-tmp.tif left.tif -b 1 -b 2 -b 3 -mask 4 -co COMPRESS=JPEG -co PHOTOMETRIC=YCBCR
gdal_translate right-tmp.tif right.tif -b 1 -b 2 -b 3 -mask 4 -co COMPRESS=JPEG -co PHOTOMETRIC=YCBCR

gdaladdo -r lanczos --config COMPRESS_OVERVIEW JPEG --config PHOTOMETRIC_OVERVIEW=YCBCR left.tif
gdaladdo -r lanczos --config COMPRESS_OVERVIEW JPEG --config PHOTOMETRIC_OVERVIEW=YCBCR right.tif

gdalbuildvrt final.vrt left.tif right.tif

Unfortunately overviews contain similar artifacts. If I omit gdaladdo step then image is OK, just loads slowly as it is missing overviews.