hsv_to_rgb不是matplotlib上的rgb_to_hsv的反转 [英] hsv_to_rgb isn't the inverse of rgb_to_hsv on matplotlib

问题描述

我试图将图像转换为hsv并返回rgb，但不知何故我丢失了颜色信息。

I tried to convert an image to hsv and back to rgb, but somehow I lost color information.

import matplotlib
import matplotlib.pyplot as plt
import matplotlib.image as mpimg

我也在shell上复制了这个问题，只是在导入后写这一行也会得到相同的结果。

And I also replicated the problem on shell too, just writing this line after importing also gives the same result.

plt.imshow(
  matplotlib.colors.hsv_to_rgb(
    matplotlib.colors.rgb_to_hsv(mpimg.imread('go2.jpg'))
  )
)

你能告诉我我做错了什么吗？

Can you tell me what am I doing wrong?

推荐答案

编辑：这只是一个部分解决方案，

请参阅 https： //github.com/matplotlib/matplotlib/pull/2569

这是一个整数除法问题。 numpy 认真对待它的类型，似乎不尊重来自__future__ import division的 。简单的解决方法是在调用 rgb_to_hsv 之前将rgb值转换为浮点值，或者修改函数：

This is an integer division issue. numpy is serious about it's types and seems to not respect from __future__ import division. The simple work around is to convert your rgb values to floats before calling rgb_to_hsv or patch the function as such:

def rgb_to_hsv(arr):
    """
    convert rgb values in a numpy array to hsv values
    input and output arrays should have shape (M,N,3)
    """
    arr = arr.astype('float')  # <- add this line
    out = np.zeros(arr.shape, dtype=np.float)
    arr_max = arr.max(-1)
    ipos = arr_max > 0
    delta = arr.ptp(-1)
    s = np.zeros_like(delta)
    s[ipos] = delta[ipos] / arr_max[ipos]
    ipos = delta > 0
    # red is max
    idx = (arr[:, :, 0] == arr_max) & ipos
    out[idx, 0] = (arr[idx, 1] - arr[idx, 2]) / delta[idx]
    # green is max
    idx = (arr[:, :, 1] == arr_max) & ipos
    out[idx, 0] = 2. + (arr[idx, 2] - arr[idx, 0]) / delta[idx]
    # blue is max
    idx = (arr[:, :, 2] == arr_max) & ipos
    out[idx, 0] = 4. + (arr[idx, 0] - arr[idx, 1]) / delta[idx]
    out[:, :, 0] = (out[:, :, 0] / 6.0) % 1.0
    out[:, :, 1] = s
    out[:, :, 2] = arr_max
    return out

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