# What is the dimension of the filters if the input image has only one channel?

I have a grayscale image with dimension HxWx1 (one channel). To build a CNN using the grayscale image as an input image, what is the dimension of the filters?

I read from some websites, it says that if the input image has only one channel, then the filter must be NxNx1. However, some other websites mentioned differently. It says even if the input image has one channel, it is fine to use filters with dimension NxNx3 by simply converting the grayscale image (HxWx1) to a RGB image (HxWx3).

Therefore, my question is: with input image that has only 1 channel, must the dimension of the filter be NxNx1 or NxNx3?

(I self-study this, so I might get the idea and understanding wrong. Help me, please.)

Note; H: height, W: width, N: height and width of the filter