将图像字节数据流解码为JPEG [英] Decode image bytes data stream to JPEG

问题描述

我正在努力从字节成功解码JPEG图像，然后再次解码回JPEG.

我从MJPG字节流的编码帧开始，我想对其进行解码以便使用OpenCV进行处理.我是Python，numpy，opencv等的新手！

我现在将文本文件中的JPG帧数据保存为:b'\ xf \ xd8 \ xff \ xdb \ x00 .... etc等，用于测试:

当我尝试在第14行(npFlat.reshape((640,480)))将numpy数组的大小调整为原始视频流分辨率(640，480)时，代码似乎失败.

** ValueError:无法将大小为228140的数组重塑为形状(640,480)*

import io
import cv2
import numpy as np

BytesFile = open('FrameBytes.txt')
MyBytes=BytesFile.read()
BytesFile.close()

dt=np.dtype(np.unit8)
dt=dt.newbtyeorder('>')

npFlat = np.fromfile('FrameBytes.txt'.dtype=dt)
npResized = npFlat.reshape(640,480,3) #CODE FAILING TO RESIZE AT THIS LINE...
cv.imshow('resized',npResized)

即使是从640、480提要中捕获了我的视频帧，还是由于某种原因，在编码过程中大小发生了变化?这是我目前所能想到的.任何帮助都欢迎.

我已经查看了相关的文章: Python-NumPy的字节图像OpenCV 使用数组但尝试避免使用PIL，并且frombuffer方法对我来说似乎也失败了.

好，所以我取得了一些进展，现在有了:

npFlat = np.frombuffer(MyBytes.encode('utf-8'),dtype=np.int8).

当我将npFlat重塑为(374，610)时，我现在还可以获得成功的代码. IE.因此374 x 610 =平面numpy数组，长度为228140 ...但是，这一切似乎都很奇怪.缓冲区信息表示一个JPG，我正尝试重新打开它...但尚未关闭.

MyBytes.txt"数据输入文件在此处可见: https://drive.google.com/file/d/18pqILl9myeTRjdiqtExFyOe94Km_ /view?usp = sharing] 1

解决方案

您已经一团糟-您应该避免将二进制数据另存为文本文件！

将文件内容复制到剪贴板中-在Mac上，命令为:

cat frame.txt | pbcopy

启动Python，并创建一个名为s的变量，并将其设置为剪贴板的内容:

s = PASTE_YOUR_CLIPBOARD

现在做:

from PIL import Image
from io import BytesIO

# Load image from BytesIO
im = Image.open(BytesIO(s))

# Display image and save image
im.show()
im.save('result.png')

如果您使用的是 OpenCV ，请使用:

import cv2

# Make s as above
s = PASTE_YOUR_CLIPBOARD

i = np.frombuffer(s,dtype=np.uint8)

im = cv2.imdecode(i,cv2.IMREAD_UNCHANGED)

cv2.imwrite('result.png',im)

I am struggling to successfully decode a JPEG image from bytes, back to JPEG again.

I started from encoded frame from a MJPG bytes stream, which I want to decode in order to manipulate with OpenCV. I am a bit of a newbie at Python, numpy, opencv etc!

I now have the frame JPG data in a text file as: b'\xf\xd8\xff\xdb\x00....etc etc for purposes of testing:

code seems to fail when I try to Resize the numpy array to the original video stream resolution (640, 480) on line 14 (npFlat.reshape((640,480))

**ValueError: cannot reshape array of size 228140 into shape (640,480)*

import io
import cv2
import numpy as np

BytesFile = open('FrameBytes.txt')
MyBytes=BytesFile.read()
BytesFile.close()

dt=np.dtype(np.unit8)
dt=dt.newbtyeorder('>')

npFlat = np.fromfile('FrameBytes.txt'.dtype=dt)
npResized = npFlat.reshape(640,480,3) #CODE FAILING TO RESIZE AT THIS LINE...
cv.imshow('resized',npResized)

Could it be that even though my video frame was captured from a 640, 480 feed, for some reason during encoding the size has changed? This is all I can think of at the moment. Any/all help welcome.

I have reviewed a related post:Python - byte image to NumPy array using OpenCV but trying to avoid PIL, and the frombuffer method also seems to be failing for me.

Ok, so I made some progress and now have:

npFlat = np.frombuffer(MyBytes.encode('utf-8'),dtype=np.int8).

I can now also get the code to succeed when I 'reshape' npFlat to (374, 610). I.e. so that 374 x 610 = the flat numpy array, which is of length 228140...but this all seems odd. the buffer information represents a JPG which I am trying to reopen...and am not getting close yet.

MyBytes.txt" Data Input File is viewable here: https://drive.google.com/file/d/18pqILl9myeTRjdiqtExFyOe94Km_aNNM/view?usp=sharing]1

解决方案

You have made quite a mess - you should avoid saving binary data as text files!

Copy the contents of your file into your clipboard - on a Mac the command is:

cat frame.txt | pbcopy

Start Python and make a variable called s and set it to the contents of the clipboard:

s = PASTE_YOUR_CLIPBOARD

Now do:

from PIL import Image
from io import BytesIO

# Load image from BytesIO
im = Image.open(BytesIO(s))

# Display image and save image
im.show()
im.save('result.png')

If you are on OpenCV, use:

import cv2

# Make s as above
s = PASTE_YOUR_CLIPBOARD

i = np.frombuffer(s,dtype=np.uint8)

im = cv2.imdecode(i,cv2.IMREAD_UNCHANGED)

cv2.imwrite('result.png',im)

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