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Error while trying to display only certain colour pixels of an image that is captured

I am trying to convert all the pixels of a captured image, that are not in the color yellow to white.

The error message that I am getting is:

if jmg[i,j]!=[255,255,0]:
valueError: the truth value of an array with more than one element is ambiguous. use a.any() or a.all()


Below is my code:

import cv2
import picamera
import numpy
import time
from matplotlib import pyplot as plt
print("ready")
with picamera.PiCamera() as camera:
camera.resolution=(400,400)
time.sleep(1)
camera.capture("/home/pi/rowdy.jpg")
print("Done")
yellow=[255,255,0]
img=cv2.imread("/home/pi/rowdy.jpg",1)
jmg=cv2.cvtColor(img,cv2.COLOR_BGR2RGB)
for i in numpy.arange(399):
for j in numpy.arange(399):
if jmg[i,j]!=[255,255,0]:
jmg[i,j]=[255,255,255]

plt.imshow(jmg)
plt.xticks(),plt.yticks()
plt.show()


2 Answers
2

jmg is a numpy array of three values. When you compare a numpy array to another array (or list, in your case), it will compare them element-wise.

jmg

element-wise

if jmg[i,j]!=[255,255,0]: #np.array(255, 0, 0) != [255,255,0]
# -> np.array(False, True, False)


This means that you need to do what the error message says and use either any() or all() to determine the value you want. In your case, you want to check if any of those values don't match, which means your element-wise logic would make one of the three values True

any()

all()

any

True

if (jmg[i,j]!=[255,255,0]).any():
jmg[i,j]=[255,255,255]


A much faster way is to use the numpy library. First create a copy of the mage and then using numpy.argwhere replace the pixel values at the required positions:

numpy

numpy.argwhere

image1 = image.copy()
image1[np.argwhere(image != [255,255,0])] = [255,255,255]


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