Hi there guys!
Today I wanna talk about image pan-sharpening in QGIS.
I don’t want to enter in deeper technical details regarding pan-sharpening algorithms or something like that. I just want to focus on visual perception and image quality, ok?
QGIS in its processing toolbox has the ability to use the Orfeo toolbox (https://www.orfeo-toolbox.org). Orfeo is a great open-source software to perform image analysis. It is really great, believe me! But when talking about pan-sharpening it lacks the ability of perform HSV fusions (https://www.orfeo-toolbox.org/CookBook/Applications/app_Pansharpening.html).
But how can this affect our work?
Lets consider that I want to perform a pan-sharpening using this following images:
Using Orfeo toolbox I can achieve the following results: (Bayes, LMVM and RCS respectively)
Looking at the results made by Orfeo we can choose the RCS output as the best looking pan-sharpened image. In my opinion, it seems to get more details of that part of the land surrounded by water on top of the image, don’t you agree?
Now, the other 2, Bayes and LMVM outputs don’t look quite good in my humble opinion. The Bayes output delivered almost no change and the LMVM output seems a bit blurred.
Considering this, you can try to perform a pan-sharpening operation using HSV fusion, but this is not available neither in QGIS (natively) nor in Orfeo toolbox.
So, having that in mind, my co-workers and I decided to develop a script to perform pan-sharpening using HSV fusion. The result of our work is available as a tool in our QGIS plugin called DSG Tools (https://plugins.qgis.org/plugins/DsgTools/). In another another opportunity I will explain more about DSG Tools.
DSG Tools is a QGIS plugin developed by the Geographic Service at Brazilian Army. It was developed to make it possible to acquire vector data in QGIS in accordance to the Brazilian Geospatial Vector Data Structure, but besides that, DSG Tools provides a considerable toolbox that allow among other things, perform pan-sharpening using HSV fusion.
The script we made can be installed into QGIS’ toolbox and it will be available in a group called DSG as we can see next:
Well, starting the script and setting its parameters (remember to superimpose the images prior the fusion – Orfeo has a tool for this) we can achieve the following result:
In my opinion, the pan-sharpened image generated by our HSV fusion script seems very close to the real terrain. Let’s now compare Orfeo’s RCS output and our HSV fusion output side by side:
Which one would you choose? I would choose the HSV fusion… But remember, this is just my opinion…
See you later! Bye!