开源motion代码分析

本帖最后由 9crk 于 2015-2-3 13:21 编辑

motion：国外的开源视频移动侦测软件，集成了ffmpeg和流媒体服务，提供运动报警（执行脚本）及录像功能（不过不支持H264）。

借花献佛，主要分析一下其运动侦测算法。

项目主页：http://sourceforge.net/projects/motion/ 源码已上传： [attach]2241[/attach] motion接口在motion.c文件中 static void motion_loop(void arg) 主要关注/ MOTION LOOP - MOTION DETECTION SECTION / 这一段代码。 [code] /* The actual motion detection takes place in the following

• diffs is the number of pixels detected as changed
• Make a differences picture in image_out

• 1.做帧差

• alg_diff_standard is the slower full feature motion detection algorithm
• alg_diff first calls a fast detection algorithm which only looks at a
• fraction of the pixels. If this detects possible motion alg_diff_standard

• is called. */

      if (cnt->threshold && !cnt->pause) {
          /* if we've already detected motion and we want to see if there's
           * still motion, don't bother trying the fast one first. IF there's
           * motion, the alg_diff will trigger alg_diff_standard
           * anyway
           */
          if (cnt->detecting_motion || cnt->conf.setup_mode)
              cnt->current_image->diffs = alg_diff_standard(cnt, cnt->imgs.image_virgin);
          else
              cnt->current_image->diffs = alg_diff(cnt, cnt->imgs.image_virgin);

  2.开关灯处理 /* Lightswitch feature - has light intensity changed?

  • This can happen due to change of light conditions or due to a sudden change of the camera
  • sensitivity. If alg_lightswitch detects lightswitch we suspend motion detection the next
  • 5 frames to allow the camera to settle.

  • Don't check if we have lost connection, we detect "Lost signal" frame as lightswitch */ if (cnt->conf.lightswitch && !cnt->lost_connection) { if (alg_lightswitch(cnt, cnt->current_image->diffs)) { if (cnt->conf.setup_mode) motion_log(-1, 0, "Lightswitch detected");

                if (cnt->moved < 5)
                    cnt->moved = 5;
    
                cnt->current_image->diffs = 0;
                alg_update_reference_frame(cnt, RESET_REF_FRAME);
            }
        }

    3.开关灯滤波 /* Switchfilter feature tries to detect a change in the video signal

  • from one camera to the next. This is normally used in the Round
  • Robin feature. The algorithm is not very safe.
  • The algorithm takes a little time so we only call it when needed
  • ie. when feature is enabled and diffs>threshold.
  • We do not suspend motion detection like we did for lightswitch

  • because with Round Robin this is controlled by roundrobin_skip. */ if (cnt->conf.switchfilter && cnt->current_image->diffs > cnt->threshold) { cnt->current_image->diffs = alg_switchfilter(cnt, cnt->current_image->diffs, cnt->current_image->image);

            if (cnt->current_image->diffs <= cnt->threshold) {
                cnt->current_image->diffs = 0;
    
                if (cnt->conf.setup_mode)
                    motion_log(-1, 0, "Switchfilter detected");
            }
        }

    4.噪点消除 /* Despeckle feature

  • First we run (as given by the despeckle option iterations
  • of erode and dilate algorithms.[color=Red]//主要使用了腐蚀与膨胀操作[/color]
  • Finally we run the labelling feature.

  • All this is done in the alg_despeckle code. */ cnt->current_image->total_labels = 0; cnt->imgs.largest_label = 0; olddiffs = 0;

        if (cnt->conf.despeckle && cnt->current_image->diffs > 0) {
            olddiffs = cnt->current_image->diffs;
            cnt->current_image->diffs = alg_despeckle(cnt, olddiffs);
        } else if (cnt->imgs.labelsize_max) {
            cnt->imgs.labelsize_max = 0; /* Disable labeling if enabled */
        }    
    
    } else if (!cnt->conf.setup_mode) {
        cnt->current_image->diffs = 0;
    }

    5.智能灵敏度设置 / Manipulate smart_mask sensitivity (only every smartmask_ratio seconds) / if (cnt->smartmask_speed && (cnt->event_nr != cnt->prev_event)) { if (!--smartmask_count) { alg_tune_smartmask(cnt); smartmask_count = smartmask_ratio; } }

    /* cnt->moved is set by the tracking code when camera has been asked to move.

• When camera is moving we do not want motion to detect motion or we will
• get our camera chasing itself like crazy and we will get motion detected
• which is not really motion. So we pretend there is no motion by setting
• cnt->diffs = 0.
• We also pretend to have a moving camera when we start Motion and when light
• switch has been detected to allow camera to settle. */ if (cnt->moved) { cnt->moved--; cnt->current_image->diffs = 0; }

[/code]

可见主要是执行了alg_diff函数。 做完帧差后，再加入了开关灯切换、开关灯滤波、 噪点清除、smartMask（灵敏度设置）

算法主要在alg.c 以下是alg.h的接口函数。

[code]void alg_locate_center_size(struct images , int width, int height, struct coord ); void alg_draw_location(struct coord , struct images , int width, unsigned char , int); int alg_diff(struct context , unsigned char ); int alg_diff_standard(struct context , unsigned char ); int alg_lightswitch(struct context , int diffs); int alg_switchfilter(struct context , int, unsigned char ); void alg_noise_tune(struct context , unsigned char ); void alg_threshold_tune(struct context , int, int); int alg_despeckle(struct context , int); void alg_tune_smartmask(struct context ); void alg_update_reference_frame(struct context , int);[/code]

[code]int alg_diff(struct context cnt, unsigned char new) { int diffs = 0;

if (alg_diff_fast(cnt, cnt->conf.max_changes / 2, new))
    diffs = alg_diff_standard(cnt, new);

return diffs;

}[/code]

主要算法接口是alg_diff，alg_diff_fast是用于减少计算量的，当帧差统计信息小于一个值时，就不执行alg_diff_standard。

分析其实现代码可以发现：噪点消除、智能灵敏度算法的主要核心还是腐蚀与膨胀操作。