Question

我用python写一些代码来打开USB相机并从中抓取帧。我将代码用于http流。对于JPEG编码，我使用libturbojpeg库。为此，我使用64位OS。

product: Raspberry Pi 3 Model B Rev 1.2
serial: 00000000f9307746
width: 64 bits
capabilities: smp cp15_barrier setend swp

我用不同的分辨率进行了一些测试。

Resolution   FPS   Time for encode
640 x 480     ~35       ~0.01
1280 x 720    ~17       ~0.028

这是我的代码

import time
import os
import re
import uvc
from turbojpeg import TurboJPEG, TJPF_GRAY, TJSAMP_GRAY
jpeg = TurboJPEG("/opt/libjpeg-turbo/lib64/libturbojpeg.so")
camera = None

import numpy as np
from threading import Thread

class ProcessJPG(Thread):

    def __init__(self, data):
        self.jpeg_data = None
        self.data = data
        super(ProcessJPG, self).__init__()

    def run(self):
        self.jpeg_data = jpeg.encode((self.data))

    def get_frame(self):
        self.frame = camera.get_frame()

global camera
dev_list = uvc.device_list()
print("devices: ", dev_list)
camera = uvc.Capture(dev_list[1]['uid'])
camera.frame_size = camera.frame_sizes[2] // set 1280 x 720
camera.frame_rate = camera.frame_rates[0] // set 30 fps

class GetFrame(Thread):
    def __init__(self):
        self.frame = None
        super(GetFrame, self).__init__()
    def run(self):
        self.frame = camera.get_frame()

_fps = -1
count_to_fps = 0
_real_fps = 0
from time import time
_real_fps = ""
cfps_time = time()

while True:
    if camera:
        t = GetFrame()
        t.start()
        t.join()
        img = t.frame
        timestamp = img.timestamp
        img = img.img
        ret = 1
    t_start = time()
    t = ProcessJPG(img)
    t.start()
    t.join()
    jpg = t.jpeg_data
    t_end = time()
    print(t_end - t_start)
    count_to_fps += 1
    if count_to_fps >= _fps:
        t_to_fps = time() - cfps_time
        _real_fps = 1.0 / t_to_fps
        cfps_time = time()
        count_to_fps = 0
    print("FPS, ", _real_fps)

编码行是：jpeg.encode((self.data))

我的问题是，是否可以将FPS提高到1280 x 720 （例如30fps）分辨率，还是应该使用功能更强大的设备？当我在计算过程中在htop上查看时，CPU使用率未达到100％。

编辑：相机格式：

[video4linux2,v4l2 @ 0xa705c0] Raw       :     yuyv422 :           YUYV 4:2:2 : 640x480 1280x720 960x544 800x448 640x360 424x240 352x288 320x240 800x600 176x144 160x120 1280x800
[video4linux2,v4l2 @ 0xa705c0] Compressed:       mjpeg :          Motion-JPEG : 640x480 1280x720 960x544 800x448 640x360 800x600 416x240 352x288 176x144 320x240 160x120

Answer 1

有可能，而且您不需要更强大的硬件。

从pyuvc README.md，

* Capture instance will always grab mjpeg conpressed frames from cameras.

当您的代码访问.img属性时，它将调用jpeg2yuv（请参见 here和 here）。然后您正在使用jpeg_encode()重新编码。之后尝试使用frame.jpeg_buffer 捕获并完全不触碰.img。

我用Logitech C310看了RPi2上的pyuvc，并做了一个简化示例，

import uvc
import time

def main():
    dev_list = uvc.device_list()
    cap = uvc.Capture(dev_list[0]["uid"])
    cap.frame_mode = (1280, 720, 30)
    tlast = time.time()
    for x in range(100):
        frame = cap.get_frame_robust()
        jpeg = frame.jpeg_buffer
        print("%s (%d bytes)" % (type(jpeg), len(jpeg)))
        #img = frame.img
        tnow = time.time()
        print("%.3f" % (tnow - tlast))
        tlast = tnow
    cap = None

main()

我每帧获得〜.033s，在〜8％CPU时达到〜30fps。如果我取消对#img = frame.img行的注释，则在99％CPU上它会达到〜.054s /帧或〜18fps（解码时间限制了捕获率）。

Raspberry Pi 3通过720p USB摄像头提高FPS

1 个答案: