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