USB攝像頭協議

Question

我想將USB攝像頭連接到嵌入式設備。我的設備操作系統是嵌入式Linux並支持USB主機。我可以輕鬆讀取和寫入USB端口，但我不知道如何從相機捕捉圖像。有沒有USB攝像頭的標準協議，我可以捕捉圖像？

Answer 1

支持此功能的大多數相機使用Picture Transfer Protocol (PTP)。在Linux中，通過libgphoto2支持很多相機。

您可以使用像列出連接設備：

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); 

（從libgphoto2-2.4.11 /例子/ autodetect.c兩者）