Patent ID: 8681126

Claim:
An optical touch-sensitive device, comprising: a screen; a rolling image capture system configured to acquire an image of the screen, the rolling image capture system comprising one or more fields of pixels; a local light source configured to illuminate the screen with local light; and a controller in electrical communication with the rolling image capture system and the local light source, wherein the controller is configured to: acquire a first frame of image data with the rolling image capture system; acquire a second frame of image data with the rolling image capture system; while acquiring the first frame of image data and the second frame of image data, operate the local light source such that each field of pixels integrates local+ambient light for a duration t local+ambient and ambient light for a duration t ambient , and such that a sum t local+ambient +t ambient for the first frame of image data is different than a sum t local+ambient +t ambient for the second frame of image data for each field of pixels; determine an ambient light value for a pixel in the image data from one or more of the first frame of image data and the second frame of image data; and adjust one or more pixels for ambient light based upon the ambient light value.