Electronic pan tilt zoom video camera with adaptive edge sharpening filter

• US 6,614,474 B1
• Filed: 08/27/1998
• Issued: 09/02/2003
• Est. Priority Date: 08/27/1998
• Status: Expired due to Term

• Current Assignee: Polycom Incorporated (Plantronics, Inc.)
• Original Assignee: Polycom Incorporated (Plantronics, Inc.)
• Inventors: Taetzsch, Steven C., Baxter, Larry K., Malkin, Kenneth W., Phelps, Daniel R.
• Primary Examiner(s): Garber, Wendy R.
• Assistant Examiner(s): Villecco, John M.
• Application Number:
  US09/141,057
• Time in Patent Office: 1,832 Days
• Field of Search: 316/252, 316/552, 316/241, 316/263, 316/625, 316/261, 316/262, 382/266, 382/268, 382/199, 382/205, 382/256, 382/270, 382/272
• US Class Current: 348/252
• CPC Class Codes: H04N 5/208 for compensating for attenuation of high frequency components, e.g. crispening, aperture distortion correction

Abstract

An apparatus and a method is provided for enhancing a digital image comprised of pixels by adaptively sharpening the pixels and clipping the numerical values of the sharpened edge pixels so as to fall between the smallest unsharpened numerical value and the greatest unsharpened numerical value, respectively, of the pixels located within a neighborhood of the pixels. Pixels which are located on an edge are sharpened in the direction perpendicular to the edge. The threshold value used to ascertain the presence of an edge and sharpening parameter used to control the degree of sharpening can be adaptively controlled by the zoom ratio. The apparatus of the invention is particularly suited for an electronic set-top video camera.

Claims

1. A method of enhancing a digital image, the image comprised of image pixels, each image pixel associated with a numerical value and residing in a neighborhood of image pixels, the method comprising the steps of:

locating edge pixels by applying an edge detector to the image pixel;

detecting for each edge pixel an edge orientation;

sharpening with a sharpening filter said edge pixel in a direction perpendicular to the edge orientation; and

limiting the sharpened numerical value of each sharpened edge pixel so as to fall between the smallest unsharpened numerical value and the greatest unsharpened numerical value of the pixels located in said neighborhood of pixels and located in a direction perpendicular to the edge orientation.

2. A method of enhancing a digital image, the image comprised of image pixels, each image pixel associated with a numerical value and residing in a neighborhood of image pixels, the method comprising the steps of:

locating edge pixels by applying an edge detector to the image pixel;

sharpening with a sharpening filter said edge pixels, the image pixels which represent local minima or maxima within the neighborhood of pixels being left unsharpened when said edge pixels are sharpened; and

limiting the sharpened numerical value of each sharpened edge pixel so as to fall between the smallest unsharpened numerical value and the greatest unsharpened numerical value of the pixels located in said neighborhood of pixels.

3. A device for enhancing a digital image comprised of image pixels, each image pixel associated with a numerical value and residing in a neighborhood of image pixels, the device comprising:

an edge detector for locating edge pixels within said neighborhood of image pixels, said edge detector capable of detecting an edge orientation of said edge pixels;

a sharpening filter for sharpening said edge pixels in a direction perpendicular to the edge orientation; and

a clipping device for limiting the numerical value of said sharpened edge pixels so as to fall between the smallest unsharpened numerical value and the greatest unsharpened numerical value of the image pixels located in said neighborhood of pixels and located in the direction perpendicular to the edge orientation.

4. A video camera system comprising:

a video camera controllable by a user and capable of acquiring a digital image comprised of pixels of an object, said video camera configured to select from said pixels a subset of pixels to form the digital image;

an image sharpening device connected to said camera and comprising;

a sharpening filter for sharpening said pixels located within a neighborhood of pixels, said sharpening filter adapted to receive a sharpening parameter for controlling the sharpening, where said sharpening parameter is large if said subset of pixels contains a small number of pixels and said sharpening parameter is small if said subset of pixels contains a larger number of pixels; and

a clipping device for limiting the sharpened numerical value of said sharpened pixels so as to fall between the smallest unsharpened numerical value and the greatest unsharpened numerical value of the pixels located within said neighborhood of pixels.