The same exact patch dot product repeats at every valid location. The result is a feature map of exact integers.
Slide the kernel
After one cell, slide the same kernel across every valid patch. With a 4 by 4 image and a 3 by 3 kernel, valid stride 1 makes a 2 by 2 feature map.
(4−3+1)×(4−3+1)
Every cell is recomputed
Every displayed feature-map cell is recomputed from its own patch. For this image and kernel, the cells are 9, -6, 6, and -9.
feature map=[96−6−9]
Summary
The feature map is not a new kind of arithmetic. It is the same exact dot product repeated at each valid location.
feature map cells are exact integer sums