changing hsv values of an image in opencv python isnt working

Question

Im trying to set the Minimum and Maximum value of HSV of an Image in opencv python but after running the code all I can see is a blank rectangle box.

import cv2
import sys
import numpy as np

# Load in image
image = cv2.imread('power.jpg')


# Set minimum and max HSV values to display
lower = np.array([0, 209, 0])
upper = np.array([179, 255, 236])

# Create HSV Image and threshold into a range.
hsv = cv2.cvtColor(image, cv2.COLOR_BGR2HSV)
mask = cv2.inRange(hsv, lower, upper)
output = cv2.bitwise_and(image,image, mask= mask)


# Display output image
cv2.imshow('image',output)

Answer 1

I was able to solve it.

import numpy as np
import cv2

img = cv2.imread( "power.jpg" )

## convert to hsv
hsv = cv2.cvtColor(img, cv2.COLOR_BGR2HSV)

## mask of red (36,0,0) ~ (70, 255,255)
mask = cv2.inRange(hsv, (0, 209, 0), (179, 255,236))
bak = img.copy()

# Show only red
#bak[mask > 0] = (0, 0, 255)
imask = mask>0
green = np.zeros_like(img, np.uint8)
green[imask] = img[imask]

## save 
cv2.imwrite("image.png", green)