程式攝影機控制參數

在先前的 Extended View System (EVS) 1.0 版本中,攝影機裝置被視為唯讀裝置,因此沒有任何方法可讓應用程式變更攝影機控制參數,例如變焦或亮度。

這可能會限制 EVS 應用程式的功能,因此新版 EVS 1.1 推出了新方法,讓應用程式能夠編寫多個相機控制參數,這些參數皆在 enum CameraParam 中定義:

/**
 * EVS Camera Parameter
 */
enum CameraParam : uint32_t {
    /**
     * The brightness of image frames
     */
    BRIGHTNESS,
    /**
     * The contrast of image frames
     */
    CONTRAST,
    /**
     * Automatic gain/exposure control
     */
    AUTOGAIN,
    /**
     * Gain control
     */
    GAIN,
    /**
     * Automatic Whitebalance
     */
    AUTO_WHITE_BALANCE,
    /**
     * Manual white balance setting as a color temperature in Kelvin.
     */
    WHITE_BALANCE_TEMPERATURE,
    /**
     * Image sharpness adjustment
     */
    SHARPNESS,
    /**
     * Auto Exposure Control modes; auto, manual, shutter priority, or
     * aperture priority.
     */
    AUTO_EXPOSURE,
    /**
     * Manual exposure time of the camera
     */
    ABSOLUTE_EXPOSURE,
    /**
     * Set the focal point of the camera to the specified position. This
     * parameter may not be effective when auto focus is enabled.
     */
    ABSOLUTE_FOCUS,
    /**
     * Enables continuous automatic focus adjustments.
     */
    AUTO_FOCUS,
    /**
     * Specify the objective lens focal length as an absolute value.
     */
    ABSOLUTE_ZOOM,
};

方法的定義如下:

/**
 * Requests to be a master client.
 *
 * When multiple clients subscribe to a single camera hardware and one of
 * them adjusts a camera parameter such as the contrast, it may disturb
 * other clients' operations. Therefore, the client must call this method
 * to be a master client. When it becomes a master, it can
 * change camera parameters until either it dies or explicitly gives up the
 * role.
 *
 * @return result EvsResult::OK if a master role is granted.
 *                EvsResult::OWNERSHIP_LOST if there is already a
 *                master client.
 */
setMaster() generates (EvsResult result);

/**
 * Sets to be a master client forcibly.
 *
 * The client, which owns the display, has a high priority and can take over
 * a master role from other clients without the display.
 *
 * @param  display IEvsDisplay handle. If this is valid, the calling client
 *                 is considered as the high priority client and therefore
 *                 it would take over a master role.
 *
 * @return result  EvsResult::OK if a master role is granted.
 *                 EvsResult::OWNERSHIP_LOST if there is already a
 *                 master client with the display.
 */
forceMaster(IEvsDisplay display) generates (EvsResult result);

/**
 * Retires from a master client role.
 *
 * @return result EvsResult::OK if this call is successful.
 *                EvsResult::INVALID_ARG if the caller client is not a
 *                master client.
 */
unsetMaster() generates (EvsResult result);

/**
 * Retrieves a list of parameters this camera supports.
 *
 * @return params A list of CameraParam that this camera supports.
 */
getParameterList() generates (vec<CameraParam> params);

/**
 * Requests a valid value range of a camera parameter
 *
 * @param  id    The identifier of camera parameter, CameraParam enum.
 *
 * @return min   The lower bound of the valid parameter value range.
 * @return max   The upper bound of the valid parameter value range.
 * @return step  The resolution of values in valid range.
 */
getIntParameterRange(CameraParam id)
    generates (int32_t min, int32_t max, int32_t step);

/**
 * Requests to set a camera parameter.
 *
 * @param  id             The identifier of camera parameter,
 *                        CameraParam enum.
 *         value          A desired parameter value.
 * @return result         EvsResult::OK if it succeeds to set a parameter.
 *                        EvsResult::INVALID_ARG if either a requested
 *                        parameter is not supported or a given value is out
 *                        of bounds.
 *         effectiveValue A programmed parameter value. This may differ
 *                        from what the client gives if, for example, the
 *                        driver does not support a target parameter.
 */
setIntParameter(CameraParam id, int32_t value)
    generates (EvsResult result, int32_t effectiveValue);

/**
 * Retrieves a value of given camera parameter.
 *
 * @param  id     The identifier of camera parameter, CameraParam enum.
 * @return result EvsResult::OK if it succeeds to read a parameter.
 *                EvsResult::INVALID_ARG if either a requested parameter is
 *                not supported.
 *         value  A value of requested camera parameter.
 */
getIntParameter(CameraParam id) generates(EvsResult result, int32_t value);

getParameterList() 會傳回可供用戶端讀取及寫入的參數清單 (CameraParam 列舉) (如果用戶端是主機),而 getIntParameterRange() 會轉送有效值範圍和解析度。當主用戶端變更攝影機參數時,同一部攝影機硬體上的所有其他用戶端都會收到通知,並取得含有參數 ID 和新值的 PARAMETER_CHANGED 事件。

注意: 感應器驅動程式可能會以不同方式處理無效的參數值。它可能只會傳回錯誤代碼,或將值截斷在有效範圍內並套用。因此,setIntParameter() 方法會傳回有效值,用戶端可以使用這個值確認要求的處理方式。

要求在多個攝影機用戶端之間進行仲裁

由於先前的 EVS 設計允許多個應用程式同時訂閱單一相機硬體,因此一個應用程式可能會透過變更相機參數,干擾其他應用程式的運作。此外,多個用戶端可能會以不同方式調整相同的參數,進而導致執行中攝影機服務出現非預期的行為。

為避免發生這類問題,EVS 管理員只允許主控用戶端編寫攝影機參數。在嘗試調整任何攝影機參數之前,用戶端必須透過呼叫 setMaster() 方法成為主用戶端。如果失敗,表示該攝影機硬體上已存在有效的主控端。在目前的主用戶端停止運作,或明確透過 unsetMaster() 放棄主用戶端角色之前,其他用戶端都無法變更攝影機參數。主用戶端傳回其權限時,所有其他應用程式都會收到 MASTER_RELEASED 事件的通知。

優先順序較高的用戶端

EVS 管理員會處理擁有高優先順序的顯示器的用戶端,並允許該用戶端從目前的主控台竊取主控台角色。由於 EVS 顯示擁有權是根據最近一次使用決定,因此新客戶甚至可以透過顯示器接管現有客戶。

高優先順序的用戶端必須呼叫 IEvsCamera::forceMaster(sp<IEvsDisplay>& display) 才能取得主控角色。EVS 管理員會檢查指定顯示器句柄的狀態,如果 (且僅當) 其狀態有效,且 DisplayState::NOT_OPENDisplayState::DEAD 都未取代主控台。剛失去主控角色的用戶端會收到 MASTER_RELEASED 事件通知,且必須妥善處理這項事件。