How to sample a R8_UINT texture in hlsl/direct12？

Question

I'm a newbie in DX12 and trying to visualize Stencil buffer onto screen. I've been copied stencil plane slice into a DXGI_FORMAT_R8_UINT texture, but when HLSL samples this texture it just returns 0, and finally my render result is a black screen.

Here is the texture2d info from PIX:

the sampling code is very straightforward, but when I debug pixel history at uv coordinate (0.398125, 0.534167), it just return a very small value from Sample expression:

 Texture2D gDiffuseMap : register(t0);  
 SamplerState gsamAnisotropicWrap : register(s4);   
 float4 PS_PixelOverdraw(VertexOut pin) : SV_TARGET 
 {     
     float4 diffuseAlbedo = gDiffuseMap.Sample(gsamAnisotropicWrap, pin.TexC);     
     return float4(diffuseAlbedo.xyz, 1.0f); 
 }  

Finally, the whole output is a black screen.