Method and apparatus for coding segmented regions which may be transparent in video sequences for content-based scalability

• US 5,974,172 A
• Filed: 02/14/1997
• Issued: 10/26/1999
• Est. Priority Date: 02/14/1997
• Status: Expired due to Fees

• Current Assignee: AT&T Corporation (AT&T, Inc.)
• Original Assignee: AT&T Corporation (AT&T, Inc.)
• Inventors: Chen, Tsuhan
• Primary Examiner(s): Tran, Phuoc
• Application Number:
  US08/801,716
• Time in Patent Office: 984 Days
• Field of Search: 348/390, 348/391, 348/26, 348/29, 348/577, 348/587, 348/592, 382/283, 382/282, 382/162, 382/164, 382/165, 382/166
• US Class Current: 382/166
• CPC Class Codes: G06T 9/001 Model-based coding, e.g. wire frame
• CPC Class Codes: G06T 9/20 Contour coding, e.g. using detection of edges
• CPC Class Codes: H04N 19/186 the unit being a colour or a chrominance component
• CPC Class Codes: H04N 9/75 Chroma key

Abstract

A method and apparatus for generating region frames from video frames are disclosed which employs an industry standard encoder to lessen the negative impact on the quality of the transmitted video sequence while consuming fewer bits. The invention utilizes image segmentation and color replacement techniques to create the region frames. Each region frame includes a subject region, zero or more previously segmented regions and zero or more non-subject regions. The subject region is defined by the pixels of the original video frame. The previously segmented regions and non-subject regions are assigned replacement pixels P_n,y and C_n, respectively. The replacement pixel C_n is chosen to indicate a color that is not likely to be confused with any color in the subject region R_n. The replacement pixels P_n,y are chosen such that the compression ratio of the region frame data is maximized. Using the region frames, content based scalability can be provided without the need for special encoders and/or channels having a wider bandwidth. The decoder may comprise color or chroma keying apparatus or circuitry keying on the replacement color C_n. Instead of keying on a single value, two thresholds may be assigned to define a boundary condition or a subject semi-transparent region. The decoder is forwarded data of the two thresholds and a flag is sent to indicate the special boundary or semi-transparent region coding. A blending process blends the foreground and background of the semi-transparent object.

Claims

1. A method for encoding video frame data, wherein said video frame data includes pixel values that define regions, said regions categorized as at least one subject region and at least one non-subject region, said method comprising:

extracting said pixel values defining a subject region of the at least one subject region from said video frame data;

assigning first and second threshold values for pixels such that one represents the subject region and the other represents the at least one non-subject region;

assigning a transparency value to said pixel values defining the subject region; and

generating encoded pixel values as a weighted summation of the pixel values defining the subject region and one of either a color coding value and background picture pixels, wherein the weighted summation is a function of the transparency value.

2. A method according to claim 1, said transparency value within the range of 0 to N, inclusive, wherein 0 corresponds to transparency and N corresponds to opacity.

3. A method according to claim 2, said weighted summation defined as:

##EQU3## where g(x,n) are the encoded pixel values;

α

(x,n) is the transparency value assigned to the subject region;

f(x,n) are the pixel values defining the subject region; and

C₀ is the one of the color coding value and the background picture pixels.

4. A method according to claim 1 for communicating the encoded video frame data further comprising steps of:

transmitting the encoded pixel values and the first and second thresholds to a decoder;

at the decoder, reconstructing the video frame data based on the encoded pixel values and the first and second thresholds.