Screen filtering boundary detection for noise filtering prior to image compositing

• US 5,557,339 A
• Filed: 05/09/1994
• Issued: 09/17/1996
• Est. Priority Date: 04/15/1993
• Status: Expired due to Term

• Current Assignee: Ultimatte Corporation (Blackmagic Design Pty Limited)
• Original Assignee: Ultimatte Corporation (Blackmagic Design Pty Limited)
• Inventors: Dadourian, Arpag
• Primary Examiner(s): Groody, James J.
• Assistant Examiner(s): LEE, MICHAEL
• Application Number:
  US08/240,881
• Time in Patent Office: 862 Days
• Field of Search: 348/584, 348/585, 348/586, 348/587, 348/588, 348/589, 348/590, 348/591, 348/592, 348/593, 348/597, 348/598, 348/599, 348/607, 348/625, 348/627, 348/630, 348/631
• US Class Current: 348/586
• CPC Class Codes: H04N 5/272 Means for inserting a foreground image in a background image, i.e. inlay, outlay
• CPC Class Codes: H04N 9/75 Chroma key

Abstract

A method and apparatus which allows different amounts of filtering to be applied to specific parts of a foreground image, thus minimizing visible noise in the backing area, while preserving fine detail information of foreground objects. The method and apparatus identify three areas within the foreground, namely unobscured backing (screen) area, screen to foreground subject transition area, foreground subject area. The area where full amount of filtering is desired is the backing area, including shadows. This is the area where the background image will be added, and if noise is present in this area, it will be added to the background image. The transition area from the screen to the foreground object requires variable amounts of filtering, depending on the width of the transition. For sharply focused edges and very fine detail, the transition width is very small, and any filtering applied there will cause blurring and softening of these edges and details. Therefore, no filtering is applied to those areas. For out of focus and moving objects, the transition width is large, and no foreground detail information is visible. In these areas, a variable amount of filtering is applied, based on the width of the transition. In this manner, noise in these transition areas is significantly reduced, without much noticeable change in already blurred edges. Within foreground subject areas, no filtering is applied, thus preserving the detail of the foreground subject.

Claims

1. In a system for compositing foreground scene and background scene video signals having red, blue and green components, said foreground scene video signals corresponding to a foreground scene and said background scene video signals corresponding to a background scene, each of said components having a corresponding video signal level, to obtain a composite video image wherein the foreground scene includes a foreground subject disposed between a colored backing and a camera, said colored backing having a luminance and visibility, said foreground scene video signals defining a portion of the colored backing area which is unobscured, an opaque foreground subject area and a transition area between said unobscured colored backing area and said opaque foreground subject area, wherein filtering is applied to portions of said foreground scene to reduce visual noise in the composite video image, the improvement comprising:

a) means (101) for generating a control signal having a level proportional to the luminance and visibility of the colored backing;

b) means (103) for adjusting the level of the control signal to match the video signal level of the red, blue and green color components of the video signal for the colored backing;

c) means (104) for subtracting the level matched control signal from the foreground scene video signals;

d) means (105, 106, 108, 109,

     110) for processing the foreground scene video signals to identify said transition area;

e) means (113) for applying a predetermined amount of filtering to said foreground scene video signals corresponding to a predetermined portion of said transition area prior to processing of said foreground scene video signals by said processing means.

5. The system defined by claim 1 further comprising:

a) means (105, 106, 108, 109,

     110) for processing the foreground scene video signals to identify said unobscured colored backing area; and

b) means (113) for applying a predetermined amount of filtering to said foreground scene video signals corresponding to said unobscured colored backing area prior to processing of said foreground scene video signals by said processing means.

2. In a method for compositing foreground scene and background scene video signals having red, blue and green components, said foreground scene video signals corresponding to a foreground scene and said background scene video signals corresponding to a background scene, each of said components having a corresponding video signal level, to obtain a composite video image wherein the foreground scene includes a foreground subject disposed between a colored backing and a camera, said foreground scene video signals defining a portion of the colored backing area which is unobscured, an opaque foreground subject area and a transition area between said unobscured color backing area and said opaque foreground subject area, wherein filtering is applied to portions of said foreground scene to reduce visual noise in the composite video image, the improvement comprising the steps of:

a) generating a control signal having a level proportional to the luminance and visibility of the colored backing;

b) adjusting the level of the control signal to match the video signal level of the red, blue and green color components of the video signal for the colored backing;

c) subtracting the level matched control signal from the foreground scene video signals;

d) processing the foreground scene video signals to identify said transition area;

e) applying a predetermined amount of filtering to said foreground scene video signals corresponding to a predetermined portion of said transition area prior to processing of said foreground scene video signals by said processing step.

6. The method defined by claim 2 further comprising the steps of:

a) processing the foreground scene video signals to identify said unobscured colored backing area; and

b) applying a predetermined amount of filtering to said foreground scene video signals corresponding to said unobscured colored backing area prior to processing of said foreground scene video signals by said processing step.

3. In a system for compositing foreground scene and background scene video signals having red, blue and green components, said foreground scene video signals corresponding to a foreground scene and said background scene video signals corresponding to a background scene, each of said components having a corresponding video signal level, to obtain a composite video image wherein the foreground scene includes a foreground subject disposed between a colored backing and a camera, said colored backing having a luminance and visibility, said foreground scene video signals defining a portion of the colored backing area which is unobscured, an opaque foreground subject area and a transition area between said unobscured colored backing area and said opaque foreground subject area, wherein filtering is applied to portions of said foreground scene to reduce visual noise in the composite video image, the improvement comprising:

a) means (101) for generating a control signal having a level proportional to the luminance and visibility of the colored backing;

b) means (103) for adjusting the level of the control signal to match the video signal level of the red, blue and green color components of the video signal for the colored backing;

c) means (104) for subtracting the level matched control signal from the foreground scene video signals;

d) means (105, 106, 108, 109,

     110) for processing the foreground scene video signals to identify said unobscured colored backing area;

e) means (113) for applying a predetermined amount of filtering to said foreground scene video signals corresponding to said unobscured colored backing area prior to processing of said foreground scene video signals by said processing means.

4. In a method for compositing foreground scene and background scene video signals having red, blue and green components, said foreground scene video signals corresponding to a foreground scene and said background scene video signals corresponding to a background scene, each of said components having a corresponding video signal level, to obtain a composite video image wherein the foreground scene includes a foreground subject disposed between a colored backing and a camera, said foreground scene video signals defining a portion of the colored backing area which is unobscured, an opaque foreground subject area and a transition area between said unobscured colored backing area and said opaque foreground subject area, wherein filtering is applied to portions of said foreground scene to reduce visual noise in the composite video image, the improvement comprising the steps of:

a) generating a control signal having a level proportional to the luminance and visibility of the colored backing;

b) adjusting the level of the control signal to match the video signal level of the red, blue and green color components of the video signal for the colored backing;

c) subtracting the level matched control signal from the foreground scene video signals;

d) processing the foreground scene video signals to identify said unobscured colored backing area;

e) applying a predetermined amount of filtering to said foreground scene video signals corresponding to said unobscured colored backing area prior to processing of said foreground video signals by said processing step.