I not a painter and I'm also 77 my body can not produce a 1px wide smooth stroke even when the brush is 1Px Round hard with the mouse or pen. I need to increase the pressure a little which may increase the stroke with.
However if the pen pressure is very light to produce a 1pixel wide stroke Photoshop paints at a low opacity not 100% opacity. How could Photoshop create a round pixel? Additionally when you use a pen with the brush tool when transfer is off I should see the brush paint at 100% opacity. May be because pixels are square and the brush tip is round. When paint is laid down Photoshop seems to do some anti-aliasing or edge softening even when Anti_alias is not checked and the brush hardness is 100%. Photoshop brush is very complex and can be customize well.
