Golang : Hue, Saturation and Value(HSV) with OpenCV example

Problem:

BGR colorspace has pixels intensity information encoded into the blue, green and red channels. You want to convert an image from RGB values to their HSV(hue, saturation, value) colorspace. How to do that in Golang and OpenCV?

Solution:

Use the opencv.CvtColor() function and set the third parameter to 40. Such as opencv.CvtColor(webCamFrameImage, webCamFrameImageHSV, 40). Why 40? It is not documented in Go-OpenCV godoc, but the integer is 40 for CV_BGR2HSV according to http://docs.opencv.org/3.1.0/df/d4e/groupimgprocc.html

Example of video feed converted to HSV from BGR:

Here you go!

 package main

 import (
  "fmt"
  "github.com/lazywei/go-opencv/opencv"
  "os"
 )

 var (
  originalWindow = new(opencv.Window)
  segmentationWindow = new(opencv.Window)
  webCamFrameImage = new(opencv.IplImage)
  webCamera = new(opencv.Capture)
 )

 func main() {
  // activate webCamera
  webCamera = opencv.NewCameraCapture(opencv.CV_CAP_ANY) // autodetect

  if webCamera == nil {
 panic("Unable to open camera")
  }

  defer webCamera.Release()

  fmt.Println("Press ESC button to quit. Must be on either one of the windows, not in terminal...")

  originalWindow = opencv.NewWindow("Video feed from camera")
  defer originalWindow.Destroy()

  segmentationWindow = opencv.NewWindow("Segmentation")
  segmentationWindow.Move(500, 100)
  defer segmentationWindow.Destroy()
  for {

 key := opencv.WaitKey(20)
 if key == 27 {
 os.Exit(0)
 }

 if webCamera.GrabFrame() {
 webCamFrameImage = webCamera.RetrieveFrame(1)
 if webCamFrameImage != nil {

 // my webcamera is HD. Have to make the image frame smaller
 // comment the immediate line to remove resize
 webCamFrameImage = opencv.Resize(webCamFrameImage, 700, 0, opencv.CV_INTER_LINEAR)

 originalWindow.ShowImage(webCamFrameImage)

 // convert BGR to HSV (Hue, Saturation, Value) colorspace
 // It is not documented in Go-OpenCV godoc, but the integer is 40 for CV_BGR2HSV
 // according to http://docs.opencv.org/3.1.0/df/d4e/group__imgproc__c.html
 webCamFrameImageHSV := webCamFrameImage.Clone()
 opencv.CvtColor(webCamFrameImage, webCamFrameImageHSV, 40)
 segmentationWindow.ShowImage(webCamFrameImageHSV)
 }
 }
  }

  os.Exit(0)

 }

References:

https://www.socketloop.com/tutorials/golang-changing-a-rgba-image-number-of-channels-with-opencv