Method and apparatus for converting a video image format to a group iii

Abstract

A video-to-FAX conversion system includes a video camera (10) for generating video signals which are then captured by a frame grabber and stored in a frame buffer (14). The data in the frame buffer is comprised of digitized values from the video signal which are stored in pixels with a first aspect ratio. A conversion device (16) is operable to map information in the frame buffer to the binary output space of a Group III FAX protocol and perform contrast enhancement thereon. The contrast enhancement includes the steps of first generating a histogram of all of the pixel values in the frame buffer (14) after expansion thereof into the output space of the Group III FAX. The histogram values are then utilized to generate an adjusted value for each of the gray scale values available for the pixels in the frame buffer 14. Each pixel in the frame buffer (14) is then expanded and the contrast enhancement applied thereto to adjust the values therein. The pixels are then processed through a dithering operation to diffuse error across the output space and then a determination is made as to whether it is a black pixel or a white pixel. This operation is done on-the-fly such that an expanded frame buffer is not required, as only a predetermined number of horizontal scan lines are required for both the contrast enhancement and image dithering operation prior to sending them to a Group III formatter (18) and, subsequently, to a Group III FAX transmitter (20) for the output of the Group III FAX.