如何在python中将RGBA图像转换为灰度? [英] How to convert an RGBA image to Grayscale in python?

问题描述

我有一个形状为(height, width, 4)的数组，即RGBA格式，我想将其转换为灰度.原始数组的RGB值为0，并且图片完全基于白色背景上的alpha值进行渲染，因此，将其转换为灰度的传统方法会失败(例如cv2.cvtColor(img,cv2.COLOR_RGBA2GRAY)).

I have array of shape (height, width, 4), i.e., RGBA format, and I want to convert this to grayscale. The original array has RGB values as 0 and the picture is rendered completely based on the alpha values over a white background, hence the traditional ways of turning this into grayscale fail (e.g., cv2.cvtColor(img,cv2.COLOR_RGBA2GRAY)).

源图像:

推荐答案

假设:

• 您的图片始终为黑白；

• Your image is always black-n-white;

白色被定义为透明；

如果这些都是真的，那么您可以直接使用Alpha频道 :

If these things are true, then you can use the Alpha channel directly:

import cv2
import matplotlib.pyplot as plt

img = cv2.imread('image.png', cv2.IMREAD_UNCHANGED)
img_gray = 255 - img[:, :, 3]

plt.imshow(img_gray, cmap='gray', vmin=0, vmax=255)
plt.show()

如果您还可以使用彩色图像，那么我想请您提供一个.

If you could also have colored images, then I would ask you to provide one.

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