Histogram not displayed after image conversion on Linux

[claudioasn]

My environment is Zorin OS 18, with QGIS 3.40.13-Bratislava. I am using a Landsat 8 dataset, both L1 and L2. The problem is that when I use image conversion, whether applying DOS (L1) or not (L2), the generated bands do not display a histogram. I tested with the original bands and the histogram works correctly; the problem starts when I use SCP.

When I say the histogram is not being displayed, it's because I'm going to the raster properties, to the histogram option, and clicking the "Calculate histogram" button. Nothing happens. The button is clickable but generates nothing. I tried changing the statistics precision from fast to real, but that didn't work either.

I tested with the same dataset on Windows, and SCP works correctly.

All dependencies are properly installed. Log attached. Thank you for your help.

log-scp.txt

[semiautomaticgit]

Hello @claudioasn ,

from the log file the preprocessing seems correct. Therefore I think it is an issue related to the QGIS version in your OS environment, considering that it works in Windows.
Maybe you can try to install a different QGIS version.

[claudioasn]

Hi @semiautomaticgit

3.40.x is the LTR version, so I believe the plugin should be working correctly, right? Unless it's requiring the installation of some specific component that isn't installed in the Linux environment but is in Windows, I imagine.

As I said, before the image goes through SCP, the histogram loads correctly. But, when I use image conversion, it's no longer displayed. Curiously, if I use the QGIS raster calculator to create a band ratio with the files that went through image conversion, the new band generated manages to load the histogram correctly. That's why, apparently, the problem involves something related to SCP in the Linux environment.

I also tested the LTS version (3.44.x), and it doesn't work either. I also tested it on a variety of computers, and on all of them the histogram doesn't load after image conversion. And this applies to other sensors, as I also tested Sentinel-2 data and the problem repeated itself.

[semiautomaticgit]

Hi @claudioasn ,

I also tested the LTS version (3.44.x), and it doesn't work either. I also tested it on a variety of computers, and on all of them the histogram doesn't load after image conversion. And this applies to other sensors, as I also tested Sentinel-2 data and the problem repeated itself.

I tested in a linux environment and I can confirm that the QGIS histogram is not displayed on a converted Landsat band.

3.40.x is the LTR version, so I believe the plugin should be working correctly, right? Unless it's requiring the installation of some specific component that isn't installed in the Linux environment but is in Windows, I imagine.

I think the problem is within the QGIS histogram that is part of QGIS software.
The SCP preprocessing works correctly as the bands are converted to reflectance (pixel values are correct), and the rasters are correctly displayed in the QGIS map.
Moreover, the output files are generated through GDAL APIs, so I tend to exclude that output rasters have issues.

As I said, before the image goes through SCP, the histogram loads correctly. But, when I use image conversion, it's no longer displayed. Curiously, if I use the QGIS raster calculator to create a band ratio with the files that went through image conversion, the new band generated manages to load the histogram correctly. That's why, apparently, the problem involves something related to SCP in the Linux environment.

Unfortunately the issue is not related to a plugin function.
Your tests confirm that it is a QGIS histogram issue probably related to the image format of the SCP output, but I can't provide a solution since it is a QGIS tool, and moreover the issue seems related to the OS since QGIS histogram works on the same output on Windows.
I can suggest to open a ticket at the QGIS repository https://github.com/qgis/QGIS/issues .
Of course if there are changes that can be implemented from the plugin side I'll be glad to implement them.