With a strong interest in Eastern ink painting and calligraphy, Nelson's success in combining his passion with technical know-how in Computer Graphics is evident. He now works on Expresii, an advanced digital painting system currently focusing on Eastern ink painting and calligraphy. In doing so, he wishes to revitalize and further develop the ancient art forms in the modern age.

Nelson's journey in digital art started when he was a teenager. Paint systems at that time could not meet the needs for organic strokes – the brushes were often a blob or some pixel-sized strings. Nelson started working on brush simulation at HKUST in 1999 and since then has been making several milestones. In 2005, he presented a paper on MoXi (a predecessor of Expresii) at SIGGRAPH, the world's most influential conference in Computer Graphics, and wowed the professionals. Adobe Systems Inc immediately reached out and licensed MoXi in 2006. MoXi was used to produce visual effect for the Opening Ceremony of the 2008 Beijing Olympics.

Also in 2008, Nelson joined Microsoft in Seattle developing another breakthrough app that simulates Western paint media before coming back to Asia in 2011, and starting to build Expresii in 2012. In 2016 Expresii became a software partner of Wacom, and 2017 was a milestone year with many exciting new initiatives happening. Nelson joined a new project, the film <Red Squirrel Mai>, the first full-length animated feature using Expresii to incorporate Eastern ink painting aesthetics. Expresii became a software partner for Microsoft Surface. Panos Panay, Corporate Vice President, Microsoft Devices, praised on stage how beautifully Expresii brings the art traditions to the digital domain at the Global Launch event of the new Microsoft Surface Pro in May 2017.

Today, Expresii is used to make digital art by users all around the world. Most recently in 2019, Nelson was invited alongside fellow alumnus Wing Keung Lo to speak at the 2021 Inaugural Conference of the Association for Chinese Animation Studies to be held at HKUST.