Green bars on top half: Calls Increasing at a strike ? Sellers betting the market won’t go up ? The strike to act as a resistance.
Green bars on the bottom half: Calls decreasing at a strike ? Sellers afraid the market might go up ? Bullish signal.
Red bars on top half: Puts Increasing at a strike ? Sellers betting market won’t go down ? The strike to act as a support.
Red bars on bottom half: Puts decreasing at a strike ? Sellers afraid the market might go down ? Bearish signal.