Golang : Select region of interest with mouse click and crop from image

Just a short Golang OpenCV program that allows the user to select a region of interest on an image with mouse click. The selected rectangular region of interest will be cropped and displayed on another window.

An example screen shot:

Here you go!

 package main

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

 var (
  win = new(opencv.Window)
  cropWindow = new(opencv.Window)
  corner1 = new(opencv.Point)
  corner2 = new(opencv.Point)
  pt = new(opencv.Point)
  leftDown = false
  leftUp = false
  image = new(opencv.IplImage)
  redColor = opencv.NewScalar(0, 0, 255, 255) // (blue, green, red, alpha)
 )

 func mouseCallBack(event, x, y, flags int, param ...interface{}) {

  // if mouse left button is pressed, record the positions and save to corner1
  if event == opencv.CV_EVENT_LBUTTONDOWN {
 leftDown = true
 corner1.X = x
 corner1.Y = y
 fmt.Printf("Corner 1 : X=%d Y=%d\n", corner1.X, corner1.Y)
  }

  if event == opencv.CV_EVENT_LBUTTONUP {
 leftUp = true
 corner2.X = x
 corner2.Y = y
 fmt.Printf("Corner 2 : X=%d Y=%d\n", corner2.X, corner2.Y)
  }

  // draw a red rectangle box when left mouse button is pressed and drag
  if (leftDown == true) && (leftUp == false) {
 pt.X = x
 pt.Y = y
 roiImage := image.Clone()
 opencv.Rectangle(roiImage, *corner1, *pt, redColor, 1, 4, 0)
 win.ShowImage(roiImage)
  }

  // crop image when both corners are populated
  if (leftDown == true) && (leftUp == true) {

 cropBoxWidth := math.Abs(float64(corner1.X) - float64(corner2.X))
 cropBoxHeight := math.Abs(float64(corner1.Y) - float64(corner2.Y))
 cropBoxX := math.Min(float64(corner1.X), float64(corner2.X))
 cropBoxY := math.Min(float64(corner1.Y), float64(corner2.Y))

 fmt.Println("X : ", cropBoxX)
 fmt.Println("Y : ", cropBoxY)
 fmt.Println("Width : ", cropBoxWidth)
 fmt.Println("Height : ", cropBoxHeight)

 // sanity check on input parameters
 // ignore if user just click on the image
 // i.e width and height equal zero

 if (cropBoxWidth != 0) && (cropBoxHeight != 0) {
 cropImage := opencv.Crop(image, int(cropBoxX), int(cropBoxY), int(cropBoxWidth), int(cropBoxHeight))
 cropWindow.Resize(int(cropBoxWidth), int(cropBoxHeight))
 cropWindow.ShowImage(cropImage)
 cropImage.Release()
 }
 leftDown = false
 leftUp = false
  }

 }

 func main() {

  if len(os.Args) != 2 {
 fmt.Printf("Usage : %s <image filename>\n", os.Args[0])
 os.Exit(0)
  }

  imageFileName := os.Args[1]

  fmt.Println("Loading image from ", imageFileName)
  fmt.Println("Press ESC key to quit")

  image = opencv.LoadImage(imageFileName)
  if image == nil {
 panic("LoadImage failed")
  }
  defer image.Release()

  win = opencv.NewWindow("Select and crop region of interest")
  win.Move(100, 100) // so that this window does not hide the crop window
  defer win.Destroy()

  cropWindow = opencv.NewWindow("Crop region of interest")
  defer cropWindow.Destroy()

  win.SetMouseCallback(mouseCallBack)
  win.ShowImage(image)

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

  os.Exit(0)
 }

References:

https://socketloop.com/tutorials/golang-put-utf8-text-on-opencv-video-capture-image-frame

https://github.com/lazywei/go-opencv/blob/master/samples/crop.go