使用gstreamer将YUVj420p像素格式转换为RGB888

Question

我正在使用gstreamer 1.2将帧从我的IP摄像机送到opencv程序

流是（640 * 368 YUVj420p），我想将其转换为RBG888，以便能够在我的opencv程序中使用它

那么有没有办法使用gstreamer进行转换？

还是我自己必须这样做？

如果是这样，请告诉我进行此转换的等式

Answer 1

经过gstreamer的一些试验后，我决定自己进行转换并且有效

首先我们必须了解YUVj420p像素格式

如上图所示，Y'UV420中的Y'，U和V分量在顺序块中分别编码。为每个像素存储Y'值，然后为每个2×2方形像素块存储U值，最后为每个2×2块存储V值。相应的Y'，U和V值使用上图中的相同颜色显示。作为来自器件的字节流逐行读取，Y'块将在位置0处找到，U块在位置x×y处（在该示例中为6×4 = 24）和位于x处的V块×y +（x×y）/ 4（这里，6×4 +（6×4）/ 4 = 30）。（复制）

这是执行它的代码（python）

此代码将说明如何使用gstreamer将帧注入opencv并进行转换

import gi
gi.require_version('Gst', '1.0')
from gi.repository import GObject, Gst
import numpy as np
import cv2

GObject.threads_init()
Gst.init(None)

def YUV_stream2RGB_frame(data):

    w=640
    h=368
    size=w*h

    stream=np.fromstring(data,np.uint8) #convert data form string to numpy array

    #Y bytes  will start form 0 and end in size-1 
    y=stream[0:size].reshape(h,w) # create the y channel same size as the image

    #U bytes will start from size and end at size+size/4 as its size = framesize/4 
    u=stream[size:(size+(size/4))].reshape((h/2),(w/2))# create the u channel its size=framesize/4

    #up-sample the u channel to be the same size as the y channel and frame using pyrUp func in opencv2
    u_upsize=cv2.pyrUp(u)

    #do the same for v channel 
    v=stream[(size+(size/4)):].reshape((h/2),(w/2))
    v_upsize=cv2.pyrUp(v)

    #create the 3-channel frame using cv2.merge func watch for the order
    yuv=cv2.merge((y,u_upsize,v_upsize))

    #Convert TO RGB format
    rgb=cv2.cvtColor(yuv,cv2.cv.CV_YCrCb2RGB)

    #show frame
    cv2.imshow("show",rgb)
    cv2.waitKey(5)

def on_new_buffer(appsink):

   sample = appsink.emit('pull-sample')
   #get the buffer
   buf=sample.get_buffer()
   #extract data stream as string
   data=buf.extract_dup(0,buf.get_size())
   YUV_stream2RGB_frame(data)
   return False

def Init():

   CLI="rtspsrc name=src location=rtsp://192.168.1.20:554/live/ch01_0 latency=10 !decodebin ! appsink name=sink"

   #simplest way to create a pipline
   pipline=Gst.parse_launch(CLI)

   #getting the sink by its name set in CLI
   appsink=pipline.get_by_name("sink")

   #setting some important properties of appsnik
   appsink.set_property("max-buffers",20) # prevent the app to consume huge part of memory
   appsink.set_property('emit-signals',True) #tell sink to emit signals
   appsink.set_property('sync',False) #no sync to make decoding as fast as possible

   appsink.connect('new-sample', on_new_buffer) #connect signal to callable func

def run():
    pipline.set_state(Gst.State.PLAYING)
    GObject.MainLoop.run()


Init()
run()

Answer 2

你是如何从相机中获取相框的？以及如何将其注入opencv应用程序？

假设你在gstreamer之外得到你的帧，你应该使用如下的管道：

appsrc caps =＆＃34; video / x-raw，format = I420，width = 640，height = 368＆＃34; ！视频转换！ capsfilter caps =＆＃34; video / x-raw，format = RGB＆＃34; ！ appsink

然后使用appsrc注入数据并使用appsink将其接收回来。如果您从http或v4l2从相机获取数据，则可以使用souphttpsrc或v4l2src替换appsrc。