USB 摄像头协议

Question

我想将 USB 摄像头连接到嵌入式设备。我的设备操作系统是嵌入式 Linux 并支持 USB 主机。我可以轻松地读取和写入 USB 端口，但我不知道如何从相机捕获图像。是否有任何标准的 USB 摄像头协议可以捕获图像？

Answer 1

大多数支持此功能的相机使用Picture Transfer Protocol (PTP)。在 Linux 中，很多相机都通过libgphoto2 支持这一点。

您可以使用以下方式列出连接的设备：

    CameraList      *xlist = NULL;

    ret = gp_list_new (&xlist);
    if (ret < GP_OK) goto out;
    if (!portinfolist) {
        /* Load all the port drivers we have... */
        ret = gp_port_info_list_new (&portinfolist);
        if (ret < GP_OK) goto out;
        ret = gp_port_info_list_load (portinfolist);
        if (ret < 0) goto out;
        ret = gp_port_info_list_count (portinfolist);
        if (ret < 0) goto out;
    }
    /* Load all the camera drivers we have... */
    ret = gp_abilities_list_new (&abilities);
    if (ret < GP_OK) goto out;
    ret = gp_abilities_list_load (abilities, context);
    if (ret < GP_OK) goto out;

    /* ... and autodetect the currently attached cameras. */
    ret = gp_abilities_list_detect (abilities, portinfolist, xlist, context);
    if (ret < GP_OK) goto out;

    /* Filter out the "usb:" entry */
        ret = gp_list_count (xlist);
    if (ret < GP_OK) goto out;
    for (i=0;i<ret;i++) {
        const char *name, *value;

        gp_list_get_name (xlist, i, &name);
        gp_list_get_value (xlist, i, &value);
        if (!strcmp ("usb:",value)) continue;
        gp_list_append (list, name, value);
    }
out:
    gp_list_free (xlist);
    return gp_list_count(list);

（取自 libgphoto2-2.4.11/examples/autodetect.c）