how to hide the number in the image render from 'custom depth stencil'

Development Cinematics & Media
1

I want to generate masks for items in a picture just like the first figure shows.

https://ss.csdn.net/p?http://mmbiz.qpic.cn/mmbiz_png/KmXPKA19gWicgib7LhNM58zLvEu3kcpoVEdAIFhCRahgLYKnVNleLWKlzMAgLx2AReQHCw4cOSr7D4qZU5PxwQgA/640?wx_fmt=png

So I rendered pictures from ‘custom depth stencil’ channel with sequences in UE4. Things went well except the numbers apearing on the mask. So is there any ways to hide the numbers in the image render from ‘custom depth stencil’ ?