IMX287延迟问题

[linoooooo]

我购买了MV-MIPI-IMX287M相机，并接入到了正点原子RK3588的开发板。在默认配置的基础上，我只修改了曝光为手动曝光，时间为5毫秒

通过V4L2读取相机数据，并通过SDL库，使用HDMI显示实时画面，发现出图延迟约为80ms,如下图所示。这要高于我们之前使用的USB3.0 工业相机（使用同样的IMX287传感器，从捕获到显示信息约50-60ms）
产品链接如下：http://www.cldkey.com/USB3camera/369.html
请问我测得的延时是合理的吗，有没有办法降低出图的延时，我们想用在目标的高精度跟踪下，可以牺牲画质，分辨率。
使用同样的传感器，MIPI相机的出图延迟是不是应该比USB3.0的相机要小呢？

这是我编写的相机数据采集代码

// v4l2_reader.h
#define BUFFER_COUNT 1

struct buffer
{
    void *start;
    size_t length;
};

class V4l2Reader : public VideoReaderManager
{
public:
    V4l2Reader();
    ~V4l2Reader();
    cv::Mat get_image() override;

private:
    int video_fd = -1;
    int subdev_fd = -1;

    struct buffer buffers[BUFFER_COUNT];
    enum v4l2_buf_type type = V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE;
};
// v4l2_reader.cpp
V4l2Reader::V4l2Reader()
{
    subdev_fd = open("/dev/v4l-subdev2", O_RDWR);
    if (subdev_fd < 0)
    {
        perror("Failed to open subdev");
        return;
    }

    struct v4l2_subdev_format fmt = {
        .which = V4L2_SUBDEV_FORMAT_ACTIVE,
        .pad = 0,
        .format = {
            .width = 704,
            .height = 544,
            .code = MEDIA_BUS_FMT_Y8_1X8,
            .field = V4L2_FIELD_NONE,
            .colorspace = V4L2_COLORSPACE_DEFAULT,
        },
    };

    if (ioctl(subdev_fd, VIDIOC_SUBDEV_S_FMT, &fmt) < 0)
    {
        perror("Failed to set subdev format");
        return;
    }

    video_fd = open("/dev/video0", O_RDWR);
    if (video_fd < 0)
    {
        perror("Failed to video device");
        return;
    }

    // 请求缓冲区
    struct v4l2_requestbuffers req = {0};
    req.count = BUFFER_COUNT;
    req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE;
    req.memory = V4L2_MEMORY_MMAP;

    if (ioctl(video_fd, VIDIOC_REQBUFS, &req) < 0)
    {
        perror("Failed to request video buf");
        return;
    }

    // 映射缓冲区
    for (int i = 0; i < BUFFER_COUNT; ++i)
    {
        struct v4l2_buffer buf = {0};
        struct v4l2_plane plane = {0};
        buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE;
        buf.memory = V4L2_MEMORY_MMAP;
        buf.index = i;
        buf.length = 1;
        buf.m.planes = &plane;

        if (ioctl(video_fd, VIDIOC_QUERYBUF, &buf) < 0)
        {
            perror("Failed to request query buf");
            return;
        }

        buffers[i].length = plane.length;
        buffers[i].start = mmap(NULL, plane.length, PROT_READ | PROT_WRITE, MAP_SHARED, video_fd, plane.m.mem_offset);
        if (buffers[i].start == MAP_FAILED)
        {
            perror("mmap");
            return;
        }
    }

    for (int i = 0; i < BUFFER_COUNT; ++i)
    {
        struct v4l2_buffer buf = {0};
        struct v4l2_plane plane = {0};
        buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE;
        buf.memory = V4L2_MEMORY_MMAP;
        buf.index = i;
        buf.length = 1;
        buf.m.planes = &plane;

        if (ioctl(video_fd, VIDIOC_QBUF, &buf) < 0)
        {
            perror("Failed to insert buf");
            return;
        }
    }

    if (ioctl(video_fd, VIDIOC_STREAMON, &type) < 0)
    {
        perror("Failed to start streaming");
        return;
    }
}

V4l2Reader::~V4l2Reader()
{
    if (ioctl(video_fd, VIDIOC_STREAMOFF, &type) < 0)
    {
        perror("Failed to stop streaming");
    }

    for (int i = 0; i < BUFFER_COUNT; ++i)
    {
        munmap(buffers[i].start, buffers[i].length);
    }

    close(subdev_fd);
    close(video_fd);
}

cv::Mat V4l2Reader::get_image()
{
    cv::Mat mat(544, 768, CV_8UC1);

    struct v4l2_buffer buf = {0};
    struct v4l2_plane plane = {0};
    buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE;
    buf.memory = V4L2_MEMORY_MMAP;
    buf.length = 1;
    buf.m.planes = &plane;

    if (ioctl(video_fd, VIDIOC_DQBUF, &buf) < 0)
    {
        perror("DQBUF failed");
        return mat;
    }

    memcpy(mat.data, buffers[buf.index].start, 768 * 544);
    cv::cvtColor(mat, mat, cv::COLOR_GRAY2BGR);

    if (ioctl(video_fd, VIDIOC_QBUF, &buf) < 0)
    {
        perror("Failed to requeue buffer");
    }

    return mat;
}

// main.cpp
int main()
{
    std::shared_ptr<V4l2Reader> v4l2_reader = std::make_shared<V4l2Reader>();
    std::shared_ptr<SdlImshow> sdl_imshow = std::make_shared<SdlImshow>(768, 544);

    cv::Mat frame;
    while (1)
    {
        frame = v4l2_reader->get_image();
        sdl_imshow->imshow(frame);
    }

    return 0;
}

[veye_xumm]

@linoooooo 你好，我们的相机内部isp流程是没有整帧缓存的，相机本身引入的delay是毫秒之内。
我觉得你这个延时主要是v4l2取图缓存和显示缓存的缘故。不过说实话SDL库我们不太懂，怎样优化需要您自己研究一下。
至于相机采集后，您这边程序直接导入算法的话，延迟肯定要比这种测量方法小的多。