The Source 2006 branch was the term used for Valve's games using technology that culminated with the release of "Half-Life 2: Episode One". HDR rendering and color correction were first implemented in 2005 using ', which required the engine's shaders to be rewritten. The former, along with developer commentary tracks, were showcased in '. "Episode One" introduced Phong shading and other smaller features. Image-based rendering technology had been in development for "Half-Life 2", but was cut from the engine before its release. It was mentioned again by Gabe Newell in 2006 as a piece of technology he would like to add to Source to implement support for much larger scenes that are impossible with strictly polygonal objects.