cv2.imdecode颜色错误（python opencv） [英] Wrong colours with cv2.imdecode (python opencv)

问题描述

我尝试显示位于此处的图像：

我使用以下代码：

  import matplotlib.pyplot as plt 
 import numpy as np 
 import urllib 
 import cv2 
 
 url ='http：//skyservice.pha.jhu。 edu / DR12 / ImgCutout / getjpeg.aspx？ra = 118.70299999999999& dec = 45.721000000000004& width = 10& height = 10& scale = 0.6'
 
 def url_to_image（url）：
 resp = urllib.request.urlopen（URL） 
 image = np.asarray（bytearray（resp.read（）），dtype = uint8）
 image = cv2.imdecode（image，cv2.IMREAD_COLOR）
返回图像
 
 img = url_to_image（url）
 plt.imshow（img）
  

并显示以下内容：

所有颜色太蓝了我尝试了各种可能性来更改 cv2.IMREAD_COLOR 的值，这些值可以在手册中，StackOverflow或网络上的其他地方找到，例如-1、0、1， cv2.COLOR_BGR2RGB ，...但是我一直无法获得正确的颜色。我尝试了 cv2.COLOR_BGR2GRAY ，它甚至没有显示为灰度。我什至尝试此答案，但是 cv2.CV_LOAD_IMAGE_COLOR 似乎不再存在...

是否存在正确的值 cv2.imdecode（）标志或plt.imshow（）的特殊颜色图，它会为我提供初始颜色吗？

方案

感谢Mark Setchell，现在可以使用了。我引用了他：

matplotlib 需要 RGB 排序，而OpenCV（相反）使用 BGR

，正确的代码是

  def url_to_image（url）：
 resp = urllib.request.urlopen（url）
 image = np.asarray（bytearray（resp.read（）），dtype = uint8）
 imageBGR = cv2.imdecode（image，cv2.IMREAD_COLOR）
 imageRGB = cv2.cvtColor（ imageBGR，cv2.COLOR_BGR2RGB）
返回图像
  

I try to display the image located here: http://skyservice.pha.jhu.edu/DR12/ImgCutout/getjpeg.aspx?ra=118.70299999999999&dec=45.721000000000004&width=10&height=10&scale=0.6

The image looks like this:

I use this code:

import matplotlib.pyplot as plt
import numpy as np
import urllib
import cv2

url = 'http://skyservice.pha.jhu.edu/DR12/ImgCutout/getjpeg.aspx?ra=118.70299999999999&dec=45.721000000000004&width=10&height=10&scale=0.6'

def url_to_image(url):
    resp = urllib.request.urlopen(url)
    image = np.asarray(bytearray(resp.read()), dtype="uint8")
    image = cv2.imdecode(image, cv2.IMREAD_COLOR)
    return image

img = url_to_image(url)
plt.imshow(img)

And it displays this:

Where all colours are too blue. I have tried various possibilities to change cv2.IMREAD_COLOR with values found in the manual, on StackOverflow or elsewhere on the net, like -1, 0, 1, cv2.COLOR_BGR2RGB, ... but I haven't been able to get the right colours. I have tried cv2.COLOR_BGR2GRAY, it didn't even show in gray scales. I even tried this answer, but cv2.CV_LOAD_IMAGE_COLORdoesn't seem to exist anymore...

Is there a correct value of cv2.imdecode() flag, or a special colormap of plt.imshow(), which would give me the initial colours?

解决方案

Thanks to Mark Setchell, it now works. I quote him:

matplotlib requires RGB ordering whereas OpenCV (perversely) uses BGR

Therefore, the correct code is

def url_to_image(url):
    resp = urllib.request.urlopen(url)
    image = np.asarray(bytearray(resp.read()), dtype="uint8")
    imageBGR = cv2.imdecode(image, cv2.IMREAD_COLOR)
    imageRGB = cv2.cvtColor(imageBGR , cv2.COLOR_BGR2RGB)
    return image

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