av/filter/basic.go

// +build !circleci

/*
DESCRIPTION
  A filter that detects motion and discards frames without motion. The
  filter uses a Mixture of Gaussians method (MoG) to determine what is
  background and what is foreground.

AUTHORS
  Ella Pietraroia <ella@ausocean.org>

LICENSE
  mog.go is Copyright (C) 2019 the Australian Ocean Lab (AusOcean)

  It is free software: you can redistribute it and/or modify them
  under the terms of the GNU General Public License as published by the
  Free Software Foundation, either version 3 of the License, or (at your
  option) any later version.

  It is distributed in the hope that it will be useful, but WITHOUT
  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
  for more details.

  You should have received a copy of the GNU General Public License
  in gpl.txt.  If not, see http://www.gnu.org/licenses.
*/

package filter

import (
	"bytes"
	"fmt"
	"image"
	"image/color"
	"image/jpeg"
	"io"
	"os"
	"strconv"
	"sync"
	"time"

	"golang.org/x/image/font"
	"golang.org/x/image/font/basicfont"
	"golang.org/x/image/math/fixed"
)

func absDiff(a, b uint32) int {
	c := int(a) - int(b)
	if c < 0 {
		return -c
	} else {
		return c
	}

}

// MOGFilter is a filter that provides basic motion detection. MoG is short for
// Mixture of Gaussians method.
type BasicFilter struct {
	dst    io.WriteCloser
	img    image.Image
	bg     [][][3]uint32
	bwImg  *image.RGBA
	w      int
	h      int
	file   io.WriteCloser
	motion int
	debug  bool
}

// NewMOGFilter returns a pointer to a new MOGFilter struct.
func NewBasicFilter(dst io.WriteCloser, debug bool) *BasicFilter {
	bwImg := image.NewRGBA(image.Rect(0, 0, 0, 0))
	var file io.WriteCloser
	var err error
	if debug {
		file, err = os.Create("motion.mjpeg")
		if err != nil {
			panic("debug file didn't create")
		}
	} else {
		file = nil
	}
	return &BasicFilter{dst, nil, nil, bwImg, 0, 0, file, 0, debug}
}

// Implements io.Closer.
// Close frees resources used by gocv, because it has to be done manually, due to
// it using c-go.
func (b *BasicFilter) Close() error {
	return nil
}

// Go routine for one row of the image to be processed
func (b *BasicFilter) Process(j int, wg *sync.WaitGroup) {
	defer wg.Done()
	for i := 0; i < b.w; i++ {
		n := b.img.At(i, j)
		R, G, B, _ := n.RGBA()

		// Compare the difference of the RGB values of each pixel to the background image.
		diffB := absDiff(B, b.bg[j][i][2])
		diffR := absDiff(R, b.bg[j][i][0])
		diffG := absDiff(G, b.bg[j][i][1])

		diff := diffR + diffG + diffB

		if diff > 45000 {
			b.motion++
		}

		if b.debug {
			if diff > 45000 {
				b.bwImg.SetRGBA(i, j, color.RGBA{0xff, 0xff, 0xff, 0xff})
			} else {
				b.bwImg.SetRGBA(i, j, color.RGBA{0x00, 0x00, 0x00, 0xff})
			}
		}

		// Update backgound image.
		copy(b.bg[j][i][:], []uint32{R, G, B})
	}
}

// Implements io.Writer.
// Write applies the motion filter to the video stream. Only frames with motion
// are written to the destination encoder, frames without are discarded.
func (b *BasicFilter) Write(f []byte) (int, error) {
	t0 := time.Now()
	// Decode MJPEG.
	r := bytes.NewReader(f)
	var err error
	b.img, err = jpeg.Decode(r)
	if err != nil {
		return 0, fmt.Errorf("image can't be decoded: %w", err)
	}

	t1 := time.Now()

	// Get background image and save a new background image if needed
	// first frame must always be sent.
	if b.bg == nil {
		bounds := b.img.Bounds()
		b.w = bounds.Max.X
		b.h = bounds.Max.Y

		b.bwImg = image.NewRGBA(image.Rect(0, 0, b.w, b.h))

		b.bg = make([][][3]uint32, b.h)
		for i, _ := range b.bg {
			b.bg[i] = make([][3]uint32, b.w)
		}

		for j := 0; j < b.h; j++ {
			for i := 0; i < b.w; i++ {
				n := b.img.At(i, j)
				R, G, B, _ := n.RGBA()
				copy(b.bg[j][i][:], []uint32{R, G, B})
			}
		}
		return len(f), nil
	}

	// Use 4x goroutines to each process one row of pixels
	j := 0
	var m sync.Mutex
	m.Lock()
	var wg sync.WaitGroup

	for j < b.h {
		wg.Add(4)
		go b.Process(j, &wg)
		go b.Process(j+1, &wg)
		go b.Process(j+2, &wg)
		go b.Process(j+3, &wg)
		j = j + 4
		wg.Wait()
	}

	if j >= b.h {
		m.Unlock()
	}

	// Will save a video of where motion is detected in motion.mjpeg (in the current folder).
	if b.debug {
		col := color.RGBA{200, 100, 0, 255}
		d := &font.Drawer{
			Dst:  b.bwImg,
			Src:  image.NewUniform(col),
			Face: basicfont.Face7x13,
			Dot:  fixed.P(20, 30),
		}
		var s string
		if b.motion > 1000 {
			s = strconv.Itoa(b.motion) + " Motion"
		} else {
			s = strconv.Itoa(b.motion)
		}
		d.DrawString(s)
		err = jpeg.Encode(b.file, b.bwImg, nil)
		if err != nil {
			return len(f), err
		}
	}

	// If there are not enough motion pixels then discard the frame.
	if b.motion < 1000 {
		return len(f), nil
	}

	// Write all motion frames.
	return b.dst.Write(f)
}