Image size after convolusion:
$frac{n-k+2p}{s}+1$
where n is the width (or height) of the image,
k is the kernel size,
p is the padding,
s is the stride.
上面公式简写为：
Image size after pooling:
$frac{n-f}{s}+1$
where n is the width (or height) of the image,
f is the pooling size,
s is the stride.