Underwater Wireless Optical Communication (UWOC) is a promising technology to enable underwater communications for exploring and monitoring marine activities due to its high bandwidth and low latency. Furthermore, underwater optical camera communication (UOCC) takes advantage of light-emitting diodes (LEDs) and cameras already embedded in underwater devices (e.g., drones). In this work, a global shutter-based UOCC system is experimentally tested under a sub-pixel condition, where the dimensions of the LED in the image plane (in µm) are smaller than a single pixel. Although the LED projection dimensions are less than a single pixel, the incoming light irradiance spreads over a limited image sensor area. The results reveal that a 2 m link with a bit rate of 8 bps per channel (24 bps in total) can be attained using an RGB LED as a transmitter and a digital camera as a receiver by applying the point spread function for the demodulation. The validation of this system in sub-pixel conditions guarantees the operation of long-distance UOCC links, where extensive LED sources are perceived as single points in the image. In addition, as the LED dimensions in the image plane are significantly small, the camera can effectively accommodate several transmitters, increasing the link throughput considerably.