Thumbs Up with a Twist - Correction and Smoothing of Grip
📝 Originally published (in Japanese) at forge.workstyle.tech . Introduction to the Fifth Article in the Series This is the fifth article in a series on creating VRM animations from live-action videos. The previous article discussed how to determine the direction to move the arm to avoid intersection. The Problem of Thumb Penetration When the thumb penetrates the index finger, simply pushing it…
This is the fifth entry in a series on crafting VRM animations from recorded real-life videos. The prior article explained how to find the right direction for moving the arm to prevent it from colliding with other body parts.
When the thumb gets stuck inside the index finger, simply pulling it out can alter the original hand shape. The aim is to have the thumb rest on top of the index finger.
The desired position for the thumb is calculated as a point 18mm from the middle of the index finger, moving towards the palm. This estimation is based on the tendency of humans to naturally place their thumb atop the index finger during gripping.
To find this position, the distance between the thumb and index finger is measured using the smallest gap between their line segments. The limit for the thumb being too close is set at 18mm, which equals the sum of the thumb and index finger radii.
There were four different ways tried to push the thumb away by rotating the base joint. However, each method ended up giving the thumb an upward position, creating an entirely different gesture.
Instead, the right way is to angle the thumb towards the index finger, rather than pushing it away. This is because when humans grasp objects, their thumb naturally aligns on top of the index finger.
To make the adjustment smoother, the "gate," which measures the amount of correction needed, is gradually modified over time. This process removes sudden spikes and fills small gaps.
However, there were five issues encountered while refining the gate. These include using a binary threshold causing the thumb to repeatedly enter and exit the index finger, applying a gate that's too weak leading to insufficient movement, adding a margin to the gate which didn't enhance the result, using a step function to adjust the gate causing the thumb to move in a step-like manner, and applying the gate to the wrong hand position resulting in incorrect thumb movement.
To refine the overall hand movement, a median filter and a Gaussian filter are applied to the hand track. This helps in smoothing out any irregularities.
In summary, the main points from this article are:
1. Define the target thumb position based on the fact it tends to rest on top of the index finger when grasping.
2. Smooth the gate over time to eliminate short bursts and fill small gaps.
3. Ensure the gate is applied to the correct hand pose to allow the thumb to move accurately.
The following article will tackle how to address the skinning issue that causes the wrist to crease.
Written by urgent.news from Dev.to's reporting — not their text. Machine-written — may contain errors; check the original before relying on it.
