Notes from stanford CS231N online course.
I am labelling the image while listening to the online course.
stride, filiter, pad
input: 7x7
F:filter:3x3
stride:N 1
padding:k
OUTPUT=(7-F)/stride+1=(7-3)/1+1=5
IF padding=1;
output=(7-F+2*K)/stride+1=(7-3+2*1)/1+1=7
IF you want to go deeper, see https://adeshpande3.github.io/A-Beginner%27s-Guide-To-Understanding-Convolutional-Neural-Networks-Part-2/