Question

我一直在研究如何将通道从BGR更改为RGB，然后就出现了。这有效，但是我对这种语法感到困惑。这种数据交换在numpy中到底如何工作？

来自gist的代码：

rgb = bgr[...,::-1]

Answer 1

...只是一个占位符，可以避免语法错误，而::-1的意思是沿最后一个维度反转数组的元素。

例如：

In [4]: rgb = np.arange(12).reshape(2,2,3)

In [5]: rgb
Out[5]: 
array([[[ 0,  1,  2],
        [ 3,  4,  5]],

       [[ 6,  7,  8],
        [ 9, 10, 11]]])
In [8]: rgb[...,::-1]
Out[8]: 
array([[[ 2,  1,  0],
        [ 5,  4,  3]],

       [[ 8,  7,  6],
        [11, 10,  9]]])

Answer 2

我不是Numpy及其操作的专家，但是我可以向您展示如何使用各种切片（索引？）技术进行某些图像处理。

通常，在RGB图像上，操作用逗号分隔，如下所示：

newImage = oldImage[ROWSTUFF, COLUMNSTUFF, CHANNELSTUFF]

ROWSTUFF，COLUMNSTUFF和CHANNELSTUFF分别由以下组成：

start:end:step

因此，让我们对该图像进行一些处理：

# Load image with PIL/Pillow and make Numpy array - you can equally use OpenCV imread(), or other libraries
im = np.array(Image.open('start.png').convert('RGB'))                                           

# im.shape is (400, 400, 3)

# Now extract top half by ending ROWSTUFF at 200
tophalf = im[:200,:,:]

# Now extract bottom half by starting ROWSTUFF at 200
bottomhalf = im[200:,:,:]

# Now extract left half by ending ROWSTUFF at 200
lefthalf = im[:,:200,:]

# Now extract right half by starting ROWSTUFF at 200
righthalf = im[:,200:,:]

# Now scale the image by taking only every 4th row and every second column:
scaled = im[::4,::2,:]

# Now extract Red channel, by setting CHANNELSTUFF to 0
red = im[:,:,0]

# Now extract Green channel, by setting CHANNELSTUFF to 1
green = im[:,:,1]

# Now flop the image top to bottom by striding backwards through ROWSTUFF
flop = im[::-1,:,:]

# Now flip the image left to right by striding backwards through COLUMNSTUFF
flip = im[:,::-1,:]

# And finally, like the question, reverse the channels by striding through CHANNELSTUFF backwards, which will make RGB -> BGR, thereby leaving Green and black unchanged
OP = im[:,:,::-1]

然后意识到...是“保留未指定尺寸的原样”的缩写形式，所以

[:,:,:,:, a:b:c] can be written as [..., a:b:c]

和

[a:b:c, :,:,:,:,:] can be written as [a:b:c, ...]

关键字：图像处理，处理，图像，Python，Numpy，翻转，翻牌，反向，步幅，开始，结束，范围，切片，切片，提取，缩放，通道，反向，BGR到RGB，RGB到BGR。

使用numpy将数据从一个通道交换到另一个通道

2 个答案: