Fine Line in Clip Studio Paint
thanks to tamomoko, I discover that SAI brushes have the ability to go down to very fine line, almost single pixel size. Krita and Photoshop also have this ability but apparently the default CSP setting doesn't.
I tested a lot of pressure settings in the brush engine for the longest time but couldn't reproduce it in CSP. For your information, I'm using Wacom Intuos 5 with a 2048-level pressure sensitivity. I think this is less of a problem for pens with higher level of pressure sensitivity.
Just the other day I found out that it is achievable by ignoring the lower end (10-15%) of the pen pressure curve.
Here it is in Clip Studio Paint (File -> Pen Pressure Settings)
Or in the Wacom tablet settings
The result is something like this, notice how big the brush circle is and compare it with the smallest hairline stroke.
In hindsight, the reason why this wasn't available with default CSP setting is obvious: when we put our pen down, because of gravity and the minimum strength of our muscle, we always apply a non-zero downward force that is bigger than 5-10% of the pressure curve. So without ignoring the first few percentages, we can't physically go down to 0 or 0.5 or 1 or 2%. (except by lifting the pen, which is an upward force and not a downward force)
(^ if someone know how to phrase this better please tell me orz)
This may not be desirable to some artists, as it affects not just size, but also opacity and other properties too.
For me, having greater control on the lower end of pressure sensitivity open up so much possibility. Readjusting for me it's not that big of a problem.