Can the output of convolution on image be higher than 255? I have probably a very simple question. When I convolve an (grayscale) image using some kernel I get some output. The original pixel can be only between 0 and 255. Is possible that the output of a convolution can be higher? Because we are creating feature map, which I understand is another image. Is the output only up to 255, do we scale it down or it does not matter?

Thanks.
It is possible.  You may have values less than 0 or greater than 255.  It will depend on the values in the kernel.  If you want to display the convolution output properly you will need to scale it first.  This process is referred to as 'normalization".