模糊是在灰度转换之后还是之前去除噪声？

Question

摘自'Learning OpenCV 3 Computer Vision with Python - Second Edition'，第50页

For blurring, let's use medianBlur(), which is effective in removing digital video noise, especially in color images. For edge-finding, let's use Laplacian(), which produces bold edge lines, especially in grayscale images. After applying medianBlur(), but before applying Laplacian(), we should convert the image from BGR to grayscale.

我很难理解为什么它建议在模糊步骤后应用灰度转换。我有一个代码，我首先应用灰度转换，我对此很好奇。你知道吗

有什么线索吗？你知道吗