/* DESCRIPTION A filter that detects motion and discards frames without motion. The filter uses a difference method looking at each individual pixel to determine what is background and what is foreground. AUTHORS Ella Pietraroia LICENSE basic.go is Copyright (C) 2020 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" "golang.org/x/image/font" "golang.org/x/image/font/basicfont" "golang.org/x/image/math/fixed" ) const debugfile = "motion.mjpeg" const ( threshold = 45000 pixels = 1000 ) type pixel struct{ r, g, b uint32 } // Basic is a filter that provides basic motion detection via a difference // method. type Basic struct { dst io.WriteCloser img image.Image bg [][]pixel bwImg *image.RGBA thresh int pix int w int h int file io.WriteCloser motion int debug bool } // NewBasic returns a pointer to a new Basic filter struct. func NewBasic(dst io.WriteCloser, debug bool, t, p int) *Basic { bwImg := image.NewRGBA(image.Rect(0, 0, 0, 0)) var file io.WriteCloser var err error file = nil if debug { file, err = os.Create(debugfile) if err != nil { panic(fmt.Sprintf("could not create debug file: %v", err)) } } return &Basic{dst, nil, nil, bwImg, t, p, 0, 0, file, 0, debug} } // Implements io.Closer. func (bf *Basic) Close() error { if bf.debug { bf.file.Close() } return nil } // 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 (bf *Basic) Write(f []byte) (int, error) { // Decode MJPEG. var err error bf.img, err = jpeg.Decode(bytes.NewReader(f)) if err != nil { return 0, fmt.Errorf("image can't be decoded: %w", err) } // First frame must be set as the first background image if bf.bg == nil { bounds := bf.img.Bounds() bf.w = bounds.Max.X bf.h = bounds.Max.Y bf.bwImg = image.NewRGBA(image.Rect(0, 0, bf.w, bf.h)) bf.bg = make([][]pixel, bf.h) for j, _ := range bf.bg { bf.bg[j] = make([]pixel, bf.w) for i, _ := range bf.bg[j] { p := bf.img.At(i, j) r, g, b, _ := p.RGBA() bf.bg[j][i].r = r bf.bg[j][i].b = b bf.bg[j][i].g = g } } return len(f), nil } // Use 4x goroutines to each process one row of pixels. var j int j = 0 var wg sync.WaitGroup for j < bf.h { wg.Add(4) go bf.process(j, &wg) go bf.process(j+1, &wg) go bf.process(j+2, &wg) go bf.process(j+3, &wg) j = j + 4 wg.Wait() } // Will save a video of where motion is detected in motion.mjpeg (in the current folder). if bf.debug { err := bf.saveFrame() if err != nil { return len(f), fmt.Errorf("image can't be encoded for debug video: %w", err) } } // If there are not enough motion pixels then discard the frame. if bf.motion < pixels { return len(f), nil } // Write all motion frames. return bf.dst.Write(f) } // Go routine for one row of the image to be processed func (bf *Basic) process(j int, wg *sync.WaitGroup) { for i, _ := range bf.bg[j] { n := bf.img.At(i, j) r, b, g, _ := n.RGBA() // Compare the difference of the RGB values of each pixel to the background image. diffR := absDiff(r, bf.bg[j][i].r) diffG := absDiff(g, bf.bg[j][i].g) diffB := absDiff(g, bf.bg[j][i].b) diff := diffR + diffG + diffB if diff > threshold { bf.motion++ } if bf.debug { if diff > threshold { bf.bwImg.SetRGBA(i, j, color.RGBA{0xff, 0xff, 0xff, 0xff}) } else { bf.bwImg.SetRGBA(i, j, color.RGBA{0x00, 0x00, 0x00, 0xff}) } } // Update backgound image. bf.bg[j][i].r = r bf.bg[j][i].b = b bf.bg[j][i].g = g } wg.Done() } func (bf *Basic) saveFrame() error { col := color.RGBA{200, 100, 0, 255} d := &font.Drawer{ Dst: bf.bwImg, Src: image.NewUniform(col), Face: basicfont.Face7x13, Dot: fixed.P(20, 30), } var s string if bf.motion > bf.pix { s = strconv.Itoa(bf.motion) + " Motion" } else { s = strconv.Itoa(bf.motion) } d.DrawString(s) return jpeg.Encode(bf.file, bf.bwImg, nil) } func absDiff(a, b uint32) int { c := int(a) - int(b) if c < 0 { return -c } else { return c } }