opencv - I want to change the colors in image with python from specific color range to another color

Question

I want to change the brown areas to RED (or another color). Just I don't know how to get the ranges for brown and put them in python code. I know how to change a single color, but not a range of colors. Any Ideas? Thanks

Answer 1

This should give you an idea - it is pretty well commented:

#!/usr/local/bin/python3
import cv2 as cv
import numpy as np

# Load the aerial image and convert to HSV colourspace
image = cv.imread("aerial.png")
hsv=cv.cvtColor(image,cv.COLOR_BGR2HSV)

# Define lower and uppper limits of what we call "brown"
brown_lo=np.array([10,0,0])
brown_hi=np.array([20,255,255])

# Mask image to only select browns
mask=cv.inRange(hsv,brown_lo,brown_hi)

# Change image to red where we found brown
image[mask>0]=(0,0,255)

cv.imwrite("result.png",image)

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How did I determine the limits for "brown"? I located a brown area in the image, and cropped it out to remove everything else. Then I resized it to 1x1 to average all the shades of brown in that area and converted it to HSV colourspace, I printed that and took the value for Hue which was 15 and went +/-5 to give a range of 10-20. Increase the range to 8-22 to select a wider range of hues.

HSV/HSL colourspace is described on Wikipedia here.

Keywords: Image processing, Python, OpenCV, inRange, range of colours, prime.