transparent pixel list values not applied to RGB raster if contrast enhancement inactive

[qgib]

Author Name: Mathieu Pellerin - nIRV (Mathieu Pellerin - nIRV)
Original Redmine Issue: 7756
Affected QGIS version: master
Redmine category:rasters

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User-added transparent pixel values are ignored when contrast enhancement is set to "no enhancement" with RGB rasters. I'm seeing this issue with LANDSAT-7 tiles

Steps to reproduce:

1. Open a new project, make sure the map canvas background color is white
2. Load a RGB-based raster (LANDSAT-7 3-band composite is perfect)
3. Open the raster's layer properties window
4. Make sure that the contrast enhancement is set to "no enhancement" in the Style tab
5. Go to the Transparency tab, and add a transparent value manually via button (set the transparency value to Red=0,Green=0,Blue=0,Percent Transparent=100
6. Apply the settings

At this stage, the raster should redraw with any black (RGB=0,0,0) value being transparent and see through. However, QGIS now fails to make the black values transparent. If you go back into the raster layer properties's Style tab and enable contrast enhancement - say "Stretch to MinMax", the user-set transparent values will be taken into account.

[qgib]

Author Name: Mathieu Pellerin - nIRV (Mathieu Pellerin - nIRV)

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Note: I'm not seeing this regression on a single band raster.

[qgib]

Author Name: Mathieu Pellerin - nIRV (Mathieu Pellerin - nIRV)

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I've actually uploaded a LANDSAT-7 3-band true color geotiff to facilitate the testing. It's available here: http://licadho-cambodia.org/raster/321.zip (64mb)

[qgib]

Author Name: Giovanni Manghi (@gioman)

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duplicate of #16651

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• resolution was changed from to duplicate
• status_id was changed from Open to Closed