I frequently need to deal with the contrast and brightness of raster layers in QGIS and I miss the tools in ArcGIS for this task. Should there be a plugin already developed for QGIS? If there is, where can one find it?
Regards.
[GIS] ny plugin for QGIS to calibrate contrast and brightness of a raster layer
imageryqgisraster
Related Solutions
This can be done in GIMP http://www.gimp.org/
You need to create a custom colour palette - this will read each image loaded and best match to the pixels forcing the colours to become a near as match.
You can also restrict contrast and brightness in a similar way
http://gimp.open-source-solution.org/manual/gimp-tool-brightness-contrast.html
http://docs.gimp.org/en/gimp-palette-dialog.html
For more advance detail you can use the Equalize function with the histogram
http://docs.gimp.org/en/gimp-layer-equalize.html
This can be automated with the script fu macro function.
I haven't calculated mode values before (most frequently occurring value), but at least for quantile values you could try to use the plugin I coded (LecoS). Although not primarily intended for this use it is able to calculate some "zonal statistics" for polygon overlays.
How to:
- Install
numpyandscipyfor your System and QGIS. On Windows choose the OSGEO4W advanced Install and select python-numpy and python-scipy. On Linux consult your linux package manager/compiler. - Download the experimental(!) LecoS plugin via the plugin downloader. The rest should be pretty self-explaining.
Please pay attention that the plugin is still experimental and calculation might fail sometimes! If you want a clear procedure suited for your needs than i would advise you to look into numpy and also R with the raster and sp packages.
I am also happy to see detailed bug reports and i will do the best i can to fix them. However if the calculation fails for you, you better lookout for other tools as well.
Best Answer
To my knowledge, there's no plugin as such (although one would be useful). But you can achieve the same effects albeit with a bit more effort, by changing the range of RGB values for that raster layer.
On the
Styletab of theLayer Propertiesdialog, you'll see a radio button markedCustom min / max valuesselect it, then play around with the numbers. With a normal colour raster, the range of each channel is (0, 255), but there's nothing stopping you actually setting values outside that range to get a certain effect. There is also aContrast enhancementoption that tells QGIS what to do when it encounters an out-of-range value; you may wantClip to MinMaxbut play around with it to see what effect it has. PressingApplyupdates the image reasonably quickly, so while not truly interactive, its certainly usable.As Giovanni says, QGIS is rapidly becoming a mature and popular project, and your support is always welcome. Funding a feature-request is the best way of getting a plug-in to do what you want.