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How to detect two different colors using `cv2.inRange` in Python-OpenCV?

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How can I define "lower" and "upper" range of two different color, such as red and blue (because red and blue are not next to each other in the HSV color)

This one belongs to red:

lower_red = np.array([160,20,70])
upper_red = np.array([190,255,255])

and this one belongs to blue:

lower_blue = np.array([101,50,38])
upper_blue = np.array([110,255,255])

I tried to combine them using if condition or make their own function but not work, can you guys show me the solution?

P/s: OpenCV in Python

like image 611
Nhiên Ngô Đình Avatar asked Jan 05 '18 08:01

Nhiên Ngô Đình


2 Answers

As you get two masks of colors, then use cv2.bitwise_or to get the final mask.

import cv2

## Read
img = cv2.imread("sunflower.jpg")

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

## mask of green (36,0,0) ~ (70, 255,255)
mask1 = cv2.inRange(hsv, (36, 0, 0), (70, 255,255))

## mask o yellow (15,0,0) ~ (36, 255, 255)
mask2 = cv2.inRange(hsv, (15,0,0), (36, 255, 255))

## final mask and masked
mask = cv2.bitwise_or(mask1, mask2)
target = cv2.bitwise_and(img,img, mask=mask)

cv2.imwrite("target.png", target)

Source:

enter image description here

Find green and yellow(the range is not that accurate):

enter image description here


BTW, to get more accurate range, here is a refer map in my related answer:

How to define a threshold value to detect only green colour objects in an image :Opencv

enter image description here

like image 164
Kinght 金 Avatar answered Oct 09 '22 08:10

Kinght 金


The below image shows the HSV Colour space, which works using Hue, Saturation & Value (or lightness).

HSV Colour Space

When working in the HSV colour space it is important to remember this and that concepts such as Red & Green are a sort-of conversion back to a different data type.

Your upper and lower boundaries can therefore only be one point in this space but can include parts of the red and blue spectrum's, i.e. purple. You would need to select threshold values that meet the criteria of whatever processing output you need.

Either that or run two separate loops, the first to threshold out the Red, and the second to threshold out your blue and then blend the two images together using OpenCV Blend functions. See here for blending two colour spaces.

like image 40
GPPK Avatar answered Oct 09 '22 08:10

GPPK