METHOD AND APPARATUS FOR THE AUTOMATIC GENERATION OF SUBJECT TO BACKGROUND TRANSITION AREA BOUNDARY LINES AND SUBJECT SHADOW RETENTION

摘要

Changes in a current image frame Cu from variations in room light level, and automatic camera adjustments, are determined and incorporated into a clear reference frame C1, thereby resulting in a zero difference in the background region when the clear frame C1 and a current frame Cu are subtracted. Any deviation from zero defines the beginning edge of a transition from background to subject. The location of the outer edge of a transition area is further refined by subtracting derivatives of the RGB signals in each frame, and by the use of a fourth color channel when available. The difference of derivitives dcu-dcl identifies the subject to background transition area, whose edges define the inner and outer boundary lines. Shadow areas on the backing are retained and may be transferred to the inserted background scene. Small areas on the backing having the same color and luminance as the subject are prevented from printing through the subject by a second "derivative" alpha channel for the small areas.