Purple Ellipse in the Center of the Screen

[heathward]

i have a 61" Hitachi LCD rear projection HDTV. about a month ago i noticed a dim purple elliptical blob in the center of the screen. i can really only see it when there are dark colors or the screen is dark when i switch inputs. it appears as if the tv is having a hard time creating blacks and dark colors in the center and instead has faded into a purplish hue. the ellipse has grown since i first noticed it and now occupies approximately half of the area of the entire screen. i bought a replacement lamp, but it did nothing to solve the problem. anybody have any ideas? could it be some sort of screen burn?