I have to process the image for Sugarcane row detection and extraction.

Sample image is accessible from the link: https://github.com/AndresHerrera/croprows_generator_pa_v2/tree/master/droneimages

I have to calculate Excess Green Vegetation Index (ExG) in QGIS to highlight green regions.

How to I compute ExG index using QGIS to have a result as in the following image:

enter image description here

  • Hi. Thanks for your input. Question: gis.stackexchange.com/questions/383807/… was w.r.t. Image Enhancement. I added a comment: "image enhancement is applied to facilitate visual interpretation and understanding of images. The enhancement will not change the radiometric values ​​of the objects in the image". I need assistance to compute ExG index using QGIS
    – HansrajR
    Jan 8, 2021 at 11:09

2 Answers 2


I would suggest OTB BandMath tool (from QGIS Processing Toolbox > OTB > Image Manipulation), which can handle bands calculation.

Given ExG = 2 * G - R - B, the corresponding OTB Expression is 2*im1b2 - im1b1 - im1b3.

(Please note im1 means the first image and each band is represented as b1 = red, b2= green and b3 = blue).

enter image description here

(Above: Output Image - used as input for this process - is the contrast enhanced image from your Raster_orthomosaic layer).

(Below: ExG output)

enter image description here

  • Thanks. I will apply your recommendations and leave you a feedback.
    – HansrajR
    Jan 8, 2021 at 11:45
  • I mistakenly posted the results as an answer. Output raster was generated but with an Error: PROJ: proj_create_from_database: cannot find proj.db.Can you kindly provide details of Tool and parameters used for contrast enhanced image.
    – HansrajR
    Jan 8, 2021 at 18:52
  • @HansrajR I think you have posted another question dedicated to the Image Enhancement. Please refine that question to focus on the issue.
    – Kazuhito
    Jan 8, 2021 at 22:23

If you have some issue with OTB, it can also be used Raster Calculator as follows:

enter image description here

After click in OK, result is totally equivalent.

enter image description here

  • Thanks for the valuable insight. Can you kindly provide details of Tool and parameters used for contrast enhanced image.
    – HansrajR
    Jan 8, 2021 at 18:09
  • 1
    I used default values as it expressed in my images. No additional details are needed.
    – xunilk
    Jan 8, 2021 at 18:38

Not the answer you're looking for? Browse other questions tagged or ask your own question.