Hello…

I am an engineering student working on a project based on NDVI calculation to monitor the crop health. I used the PiNoIR camera with blue filter for my experiment in order to obtain the values of NIR and Red region. I used the following code to extract the required values and to calculate the NDVI. But in the output image, the empty regions (area where no leaves are present as shown in the below figure) and ground have higher NDVI values. The shadowed regions are shown in the range 0.5 to 0.6. I wanted to know whether the output is correct and what corrections can be done in the -code in order to correct the error. The code is given below.

from PIL import Image

import numpy as np

import cv2

from cv2 import imread

from matplotlib import cm

rgb_matrix =cv2.imread(‘inputimg.jpg’)

w=rgb_matrix.shape[1] #columns

h=rgb_matrix.shape[0] #rows

print(w)

print(h)

#Compute ndvi values for each pixel

#NDVI=(NIR-R)/(NIR+R)

res=[]

for i in range(h):

row=[]

for j in range(w):

val=rgb_matrix[i][j]

n=val[2]

r=val[1]

num=((int(n)-int®))

den=((int(n)+int®))

if(den == 0):

r=0.0

else:

r=np.divide(num,den)

row.append®

res.append(row)

print(‘Done’)

#based on NDVI values, give different colors for easier identification

for i in range(h):

for j in range(w):

if(res[i][j] >=-1 and res[i][j] <0):

rgb_matrix[i][j]=[128,128,128] #grey

elif(res[i][j]>=0 and res[i][j]<0.2):

rgb_matrix[i][j]=[64,255,0] #parrot green

elif(res[i][j]>=0.2 and res[i][j]<0.3):

rgb_matrix[i][j]=[125,255,255] #yellow

elif(res[i][j]>=0.3 and res[i][j]<0.4):

rgb_matrix[i][j]=[0,128,128] #dark green

elif(res[i][j]>=0.4 and res[i][j]<0.5):

rgb_matrix[i][j]=[255,255,0] #sky blue

elif(res[i][j]>=0.5 and res[i][j]<0.6):

rgb_matrix[i][j]=[255,51,153] #purple

elif(res[i][j]>=0.6 and res[i][j]<0.7):

rgb_matrix[i][j]=[0,128,255] #orange

elif(res[i][j]>=0.7 and res[i][j]<0.8):

rgb_matrix[i][j]=[255,43,255] #pink

elif(res[i][j]>=0.8 and res[i][j]<0.9):

rgb_matrix[i][j]=[40,40,255] #red

else:

rgb_matrix[i][j]=[255,0,0] #dark blue

cv2.imwrite(‘outputimg.jpg’,rgb_matrix)

print(“Completed!!”)

(Ignore the indentation errors)

# NDVI Calaculation Using PiNoir camera

the code you put in does not seem to be the Custom Script supported by Sentinel Hub so I assume you were executing this in some other environment?

It’s difficult to assess, whether the output is correct or not as there are no input data provided.

As a side note, are you aware about the Sentinel Hub Custom Scripts contest? You have time until end of January to submit the script and win the prize. There is even a special one for student groups.

https://www.sentinel-hub.com/contest