# NDVI calculation using image taken from PI Noir Camera

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 matplotlib import cm
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)

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 matplotlib import cm
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)

I moved this topic to the S2 section of this forum:
https://forum.step.esa.int/c/s2tbx/6