【code基础】skimage.transform.resize的一些理解

skimage.transform.resize(order, preserve_range)

order: 插值的方法0-5：0-最近邻；1-双线性；

https://blog.csdn.net/qq_34798326/article/details/84976243

skimage在读使用io.imread读取灰度图像时（as_grey=True / as_gray=True）会做归一化处理数据类型转化为float64；

图像缩放transform.resize同样会将uint8的图像转化为float64类型，这里注意的是！！！！！！！如果已经归一化，但是类型依然是uint8的图像，在缩放之后图像的范围将不再是（0-1）。
主要在resize方面，cv2.resize就是单纯调整尺寸，而skimage.transform.resize会顺便把图片的像素归一化缩放到(0,1)区间内；

preserve_range : bool, optional
        Whether to keep the original range of values. Otherwise, the input
        image is converted according to the conventions of `img_as_float`.

通过在代码里设置preserve_range=True就可以保持原来的模式了。

https://scikit-image.org/docs/dev/api/skimage.transform.html?highlight=resize#skimage.transform.resize

 

发现使用skimage.transform.resize之后，语义分割标签图像的数值发生了改变，数据类型也发生了改变，最关键的是数值发生也发生了改变；仔细查阅官方文档，添加anti_aliasing=False选项即可，因为默认是进行高斯滤波的；

from skimage import io, transform, color
import numpy as np
print('skimage: ', skimage.__version__)
a=np.zeros((20, 20))
a[2:8, 1:3]=1
a[1:3, 4:9]=2
a[3:9, 6:8]=2
print(a)
print(a.shape)
print(a.dtype)
print(np.unique(a))
b = skimage.transform.resize(a,(10, 10),mode='constant', order=0, anti_aliasing=False, preserve_range=True)
print(b)
print(b.shape)
print(b.dtype)
print(np.unique(b))

label = skimage.io.imread('sample800/label/0705_1.png')
print(label.shape) #(800, 800)
print(label.dtype)
print(np.unique(label))
lbl = skimage.transform.resize(label,(512, 512),mode='edge', order=0, anti_aliasing=False, preserve_range=True)
print(lbl.shape)
print(lbl.dtype)
print(np.unique(lbl))
label_show = np.zeros((512, 512, 3), dtype=np.uint8)
COLORS = [(0, 0, 0), (0, 255, 0), (0, 0, 255), (238, 18, 137), (162, 205, 90), (70, 130, 180), (238, 238, 0), (255, 69, 0), (205, 145, 158), (238, 92, 66), (144, 238, 144),
          (124, 205, 124), (0, 229, 238), (151, 255, 255), (205, 190, 112)]
for i in range(1, 9):
    label_show[lbl==i]=COLORS[i]
import cv2
cv2.imshow("label_img", label_show)
cv2.waitKey(1)

description：

anti_aliasingbool, optional
Whether to apply a Gaussian filter to smooth the image prior to downsampling. It is crucial to filter when downsampling the image to avoid aliasing artifacts. If not specified, it is set to True when downsampling an image whose data type is not bool.

 不知道为什么 preserve_range 不起作用？？？？？

参考

1. 踩坑：skimage中对图像做的归一化处理；

2. skimage.transform.resize；

3. skimage_github_issue；

完