将YUV导入为字节数组 [英] Import YUV as a byte array

问题描述

我正在一个项目中，我必须对YUV420_SP_NV21图像(从Android摄像头拍摄)应用阈值，以确定哪些像素是黑色"，哪些像素是白色".

I'm working on a project where I have to apply threshold to a YUV420_SP_NV21 image (taken from an Android camera) to determine which pixels are 'black' and which are 'white'.

因此，我想将其作为字节数组(使用OpenCV，NumPy，PIL等)导入Python中，以便可以对Y值进行一些快速的按位运算.

Therefore, I want to import it in Python as a bytearray (using OpenCV, NumPy, PIL, ...), so I can do some quick bitwise operations on the Y-values.

但是，当我尝试使用以下方法导入图像时，会得到无用的输出:

However, when I try to import the image using the following methods, I get useless outputs:

当我键入

import cv2
import numpy as np

img = cv2.imread('test.yuv')
imgArr = np.array(img)

print(img)
print(imgArr)

我得到输出:

None
None

当我键入

And when I type

import numpy as np

f = open('test.yuv', 'rb')
img = f.read()
imgArr = np.array(img)

我得到了一些无用的字符序列.
当我现在输入时(例如)

I get some useless character sequence.
And when I type now (for exemple)

print(imgArr[0])

我得到输出:

IndexError: too many indices for array

这意味着imgArr根本没有数组！

Which means imgArr is no array at all!

谁能告诉我我做错了吗? 预先感谢！

Can anyone please tell me what I'm doing wrong? Thanks in advance!

推荐答案

您确实应该提供示例图像，以便人们可以更好地帮助您-否则，他们花了很长时间开发代码，以猜测是您想要的图像格式，并且如果他们猜错了，那是浪费精力.

You really should provide a sample image so folks can help you better - else they spend ages developing code for what they guess is the image format you mean and it is a waste of effort if they guess wrong.

假设您的数据来自 Wikipedia ，则您可以看到所有Y样本首先是所有U样本和所有V样本.但是，U/V样本只有Y样本的1/4倍，因为这两个分量在水平和垂直方向上都以2:1的比例进行了二次采样:

Assuming your data look like this from Wikipedia, you can see that all the Y samples come first, followed by all the U samples and all the V samples. However there are only 1/4 as many U/V samples as Y samples because these two components are subsampled at 2:1 ratio both horizontally and vertically:

因此，我们的想法是读取整个YUV样本集，然后将第一个w*h字节作为Y值，接下来的w*h/4个样本作为U，将接下来的w*h/4个样本作为V:

So, the idea is to read in the entire set of YUV samples, then take the first w*h bytes as the Y values, the next w*h/4 samples as U and the next w*h/4 samples as V:

import numpy as np

# Guess a width and height and derive number of pixels in image
w,h = 2048,1536
px = w*h

# Read entire file into YUV
YUV = np.fromfile('NV21_2048x1536.yuv',dtype='uint8')

# Take first h x w samples and reshape as Y channel
Y = YUV[0:w*h].reshape(h,w)

# Take next px/4 samples as U
U = YUV[px:(px*5)//4].reshape(h//2,w//2)

# Take next px/4 samples as V
V = YUV[(px*5)//4:(px*6)//4].reshape(h//2,w//2)

# Undo subsampling of U and V by doubling height and width
Ufull = U.copy().resize((w,h))
Vfull = V.copy().resize((w,h))

我不知道你下一步打算做什么，所以我现在就把它留在那儿！

I have no idea what you plan to do next, so I'll leave it at that for now!

关键字:NV21，YUV，YUV420，Android，YUV430P，枕头，PIL，Python，图像，图像处理.

Keywords: NV21, YUV, YUV420, Android, YUV430P, Pillow, PIL, Python, image, image processing.

这篇关于将YUV导入为字节数组的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！