title: Convolution neural networks -- all feature maps are black(pixel value is 0)
body: <p>I am doing a project that maps trained CNNs on Zynq Soc. I trained a Lenet in tensorflow and extracted weights and biases. As far as I observed, the value of weights are all close to 0, almost none of them larger than 1. But the input data of lenet is gray scale image and the pixel value is from 0 to 255. </p>
  
  <p>When I tried to do 2-D convolution between input image and kernel (trained weights), the output feature maps are all black image since the convolution result are all close to 0. Even takes Relu layer into account. But as shown in this picture below, the value of weight in the kernel and feature maps should be a value between 0 to 255 according to the brightness. </p>
  
  <p>I just wonder why I got black(0 pixel value) feature maps?</p>
  
  <p><a href="https://i.stack.imgur.com/gNNeO.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/gNNeO.png" alt="enter image description here"></a></p>