android4.0 FaceDetection笔记

╰半夏微凉° 2022-09-17 07:30 73阅读 0赞

这几天研究了下andoid4.0.3的FaceDetection这里写一下大致的流程，方便日后查阅。

相关说明可以在这里找到:

frameworks/base/docs/html/guide/topics/media/camera.jd

起始代码可以在camera.jd里找到也可以在

packages/apps/Camera/src/com/android/camera/Camera.java里找到，具体代码我就不说了.

一般起始点是startFaceDetection函数

startFaceDetection函数大致内容如下:

/*Your application must start the face detection function each time you start (or restart) the
    camera preview. Create a method for starting face detection so you can call it as needed, as shown
    in the example code below.*/
    
    public void startFaceDetection(){
        // Try starting Face Detection
        ....
        // start face detection only *after* preview has started
        if (params.getMaxNumDetectedFaces() > 0){
            // camera supports face detection, so can start it:
            mCamera.startFaceDetection();
        }
    }

首先判断硬件是否支持该功能

getMaxNumDetectedFaces函数在

frameworks/base/core/java/android/hardware/Camera.java

内容如下:

/**
             * Gets the maximum number of detected faces supported. This is the
             * maximum length of the list returned from {@link FaceDetectionListener}.
             * If the return value is 0, face detection of the specified type is not
             * supported.
             *
             * @return the maximum number of detected face supported by the camera.
             * @see #startFaceDetection()
             */
            public int getMaxNumDetectedFaces() {
                return getInt(KEY_MAX_NUM_DETECTED_FACES_HW, 0);
            }

而KEY\_MAX\_NUM\_DETECTED\_FACES\_HW一般是在ＨＡＬ层initDefaultParameters函数里设置的，设置如下

p.set(CameraParameters::KEY_MAX_NUM_DETECTED_FACES_HW, "1"); //add by dao set the max face detectctor number

initDefaultParameters里类似这样的代码，其它的我就不贴出来了.

mCamera.startFaceDetection();这个是执行的

frameworks/base/core/java/android/hardware/Camera.java里的startFaceDetection函数,内容如下:

/**
 * Starts the face detection. This should be called after preview is started.
 * The camera will notify {@link FaceDetectionListener} of the detected
 * faces in the preview frame. The detected faces may be the same as the
 * previous ones. Applications should call {@link #stopFaceDetection} to
 * stop the face detection. This method is supported if {@link
 * Parameters#getMaxNumDetectedFaces()} returns a number larger than 0.
 * If the face detection has started, apps should not call this again.
 *
 * When the face detection is running, {@link Parameters#setWhiteBalance(String)},
 * {@link Parameters#setFocusAreas(List)}, and {@link Parameters#setMeteringAreas(List)}
 * have no effect. The camera uses the detected faces to do auto-white balance,
 * auto exposure, and autofocus.
 *
 * If the apps call {@link #autoFocus(AutoFocusCallback)}, the camera
 * will stop sending face callbacks. The last face callback indicates the
 * areas used to do autofocus. After focus completes, face detection will
 * resume sending face callbacks. If the apps call {@link
 * #cancelAutoFocus()}, the face callbacks will also resume.
 *
 * After calling {@link #takePicture(Camera.ShutterCallback, Camera.PictureCallback,
 * Camera.PictureCallback)} or {@link #stopPreview()}, and then resuming
 * preview with {@link #startPreview()}, the apps should call this method
 * again to resume face detection.
 *
 * @throws IllegalArgumentException if the face detection is unsupported.
 * @throws RuntimeException if the method fails or the face detection is
 * already running.
 * @see FaceDetectionListener
 * @see #stopFaceDetection()
 * @see Parameters#getMaxNumDetectedFaces()
 */
 public final void startFaceDetection() {
 if (mFaceDetectionRunning) {
 throw new RuntimeException("Face detection is already running");
 }
 _startFaceDetection(CAMERA_FACE_DETECTION_HW);
 mFaceDetectionRunning = true;
 }

\_startFaceDetection在ＪＮＩ里,CAMERA\_FACE\_DETECTION\_HW这里初始化值是0在这个文件的开始有定义

在frameworks/base/core/jni/android\_hardware\_Camera.cpp我们可以找到\_startFaceDetection对应的函数:

{ "_startFaceDetection",
        "(I)V",
        (void *)android_hardware_Camera_startFaceDetection },

对应:android\_hardware\_Camera\_startFaceDetection,内容如下:

static void android_hardware_Camera_startFaceDetection(JNIEnv *env, jobject thiz,
 jint type)
 {
 LOGV("startFaceDetection");
 JNICameraContext* context;
 sp<Camera> camera = get_native_camera(env, thiz, &context);
 if (camera == 0) return;
 
 status_t rc = camera->sendCommand(CAMERA_CMD_START_FACE_DETECTION, type, 0);
 if (rc == BAD_VALUE) {
 char msg[64];
 snprintf(msg, sizeof(msg), "invalid face detection type=%d", type);
 jniThrowException(env, "java/lang/IllegalArgumentException", msg);
 } else if (rc != NO_ERROR) {
 jniThrowRuntimeException(env, "start face detection failed");
 }
 }

这里camera->sendCommand对应

device/samsung/common/s5p/libcamera/SecCameraHWInterface.cpp文件里的sendCommand函数,内容如下

status_t CameraHardwareSec::sendCommand(int32_t command, int32_t arg1, int32_t arg2)
    {
        return BAD_VALUE;
    }

到这里调用就结束了。

不同的产家camera的库所存放的目录可能不一样,同时这个函数需要根据具体的要求，进行修改.  
资料参考:http://blog.csdn.net/qq69696698/article/details/7325772