Bug report #10507

Overlapping points lead to increased lightness

Added by Johannes Kroeger over 8 years ago. Updated almost 4 years ago.

Category:Map Canvas
Affected QGIS version:2.2.0 Regression?:No
Operating System: Easy fix?:No
Pull Request or Patch supplied:No Resolution:end of life
Crashes QGIS or corrupts data:No Copied to github as #:18917


If you have overlapping features (I noticed with points and only tested with points), their colors will "stack" even when there is no blending chosen.

I have attached an image and a shapefile. The shapefile has 5 groups of overlapping points. The left most group has 16 points stacked on top of each other (copy'n'pasted), the next one 8, then 4 and 2. The right most is just 1 point feature.

In the image the top row is styled with a single symbol using the color "226, 255, 94" (RGB, chosen randomly as bright color). The graduated and the categorized rows both use the Spectral scheme from Color Brewer on the "id" column (which is '1' for all features). The points are 0.001 map units big and have no border.

I chose a black background, but it is visible on white just as well. I used no blending options. It does not matter if the "less jagged lines" option in rendering options is ticked or not, I saw no difference. I have not tested various outputs from the composer. This is when looking at the normal map canvas.

In the image you can see that the more points are stacked on top of each other, the brighter the spot appears in the canvas. Instead it should be using the color of whatever feature is on "top" by whatever metric QGIS uses for that. If all points are styled with the same color, there should be no visible difference between the groups, regardless of the amount of "underlying" point features.

QGIS version 2.3.0-Master QGIS code revision dcbf893
Compiled against Qt 4.8.6 Running against Qt 4.8.6
Compiled against GDAL/OGR 1.11.0 Running against GDAL/OGR 1.11.0
Compiled against GEOS 3.4.2-CAPI-1.8.2 Running against GEOS 3.4.2-CAPI-1.8.2 r3921
PostgreSQL Client Version 9.3.4 SpatiaLite Version 4.1.1
QWT Version 6.1.0 PROJ.4 Version 480
QScintilla2 Version 2.8.1

points.shp.zip (1.34 KB) Johannes Kroeger, 2014-06-09 05:49 AM

qgis_lightness_bug.png (2.73 KB) Johannes Kroeger, 2014-06-09 05:49 AM

points.png (1.31 KB) Nathan Woodrow, 2014-06-09 05:59 AM

point_stacking.png (1.57 KB) Tobias Schneider, 2014-06-10 01:52 AM


#1 Updated by Nathan Woodrow over 8 years ago

I don't see that effect here:

#2 Updated by Johannes Kroeger over 8 years ago

I forgot to state that this only occurs when you zoom out so much that the points get tiny (like in my image). Nathan confirmed seeing the issue then in IRC.

#3 Updated by Tobias Schneider over 8 years ago

I can confirm this not for the colour change, but for the anti-aliasing of the border (See picture).

#4 Updated by Giovanni Manghi almost 6 years ago

  • Regression? set to No
  • Easy fix? set to No

#5 Updated by Giovanni Manghi almost 4 years ago

  • Resolution set to end of life
  • Status changed from Open to Closed

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