System and method for displaying closed caption data on a PC monitor

• US 5,543,850 A
• Filed: 01/17/1995
• Issued: 08/06/1996
• Est. Priority Date: 01/17/1995
• Status: Expired due to Term

• Current Assignee: NVIDIA Corporation
• Original Assignee: Cirrus Logic Incorporated
• Inventors: Yonker, Michael A., Xu, Frank L., Pratt, Kyle A.
• Primary Examiner(s): Kostak, Victor R.
• Application Number:
  US08/373,617
• Time in Patent Office: 567 Days
• Field of Search: 348/468, 348/563, 348/564, 348/473, 348/476
• US Class Current: 348/617
• CPC Class Codes: H04N 7/0255 Display systems therefor
• CPC Class Codes: H04N 7/035 Circuits for the digital non-picture data signal, e.g. for slicing of the data signal, for regeneration of the data-clock signal, for error detection or correction of the data signal
• CPC Class Codes: H04N 7/0885 for the transmission of subtitles

Abstract

An apparatus for capturing and decoding the closed caption data from a television signal and displaying the closed caption data, along with the video picture, in a windowing environment on the monitor of a personal computer system. The closed caption decoder device stores the line of video data containing the closed caption text in an object in the frame buffer of the PC. The host CPU reads the raw video data from the frame buffer and stores it in system memory. The host CPU parses the line of video data to separate the two ASCII characters representing closed caption data from the color burst information and synchronizing clock information. After the closed caption data has been retrieved and parity-checked, the closed caption data may be displayed in a window of user-determined size and location on the monitor of the PC, independent of the size and location of the video image window corresponding to the closed caption text.

Claims

1. A closed caption decoder for capturing closed caption data from a television signal and displaying said closed caption data in a window of user-defined size and location on a screen of a video monitor, said decoder comprising:

a video input port for receiving said television signal;

a video processor coupled to said video input port, said video processor operable to capture at least one line of video data from a frame of said television signal, wherein said closed caption data is stored in said at least one line of video data;

a frame buffer memory coupled to said video processor for storing only a portion of said at least one line of video data; and

a second processor coupled to said video processor and to said frame buffer memory for retrieving said portion of at least one line of video data from said frame buffer memory and translating said closed caption data stored in said at least one line of video data into a first ASCII character and a second ASCII character.

2. The closed caption decoder as set forth in claim 1 wherein said second processor further comprises:

means for detecting a plurality of clock pulses contained in said at least one line of video data and determining a logical "1" value associated with a peak amplitude of said plurality of clock pulses, a logical "0" value associated with a blanking level of said at least one line of video data and located between said plurality of clock pulses, and a clock period associated with a frequency of said clock pulses.

3. The closed caption decoder as set forth in claim 2 wherein said second processor further comprises:

means for detecting a start bit associated with said closed caption data, said start bit having an amplitude greater than said logical "1" value.

4. The closed caption decoder as set forth in claim 3 wherein said second processor further comprises:

means for translating said closed caption data into said first and second ASCII characters, wherein said translating means reads a plurality of sampled values of said at least one line of video data at a plurality of intervals after said start bit, each one of said plurality of intervals being a multiple of said clock period, and compares said sampled values to said logical "1" value and said logical "0" value.

5. The closed caption decoder as set forth in claim 4 wherein said second processor further comprises:

means for displaying at least one of said ASCII characters in said window.

6. The closed caption decoder as set forth in claim 4 wherein said second processor further comprises:

means for determining if said first ASCII character is a printable character or a control character.

7. The closed caption decoder as set forth in claim 4 wherein said second processor further comprises:

means for checking the parity of said first and second ASCII characters.

8. The closed caption decoder as set forth in claim 1 wherein said video processor stores only every other pair of pixel data contained in said at least one line of video data.

9. A closed caption decoder for capturing closed caption data from a television signal and displaying the closed caption data in a window of user-defined size and location on a screen of a video monitor, said decoder comprising:

a video input port for receiving said television signal;

a video processor coupled to said video port, said video processor operable to capture a line of video data containing said closed caption data from a frame of said television signal and store only a portion of said line of video data in a frame buffer memory coupled to said video processor as a plurality of pixel data, said pixel data comprising intensity data and color data; and

a second processor coupled to said video processor and to said frame buffer for reading from said frame buffer memory a plurality of said intensity data and translating said intensity data into two ASCII characters.

10. The closed caption decoder as set forth in claim 9 wherein said video processor stores only every other pair of pixel data contained in said line of video data.

11. The closed caption decoder as set forth in claim 9 wherein said second processor further comprises:

means for detecting a plurality of clock pulses contained in said line of video data and determining a logical "1" value associated with a peak amplitude of said plurality of clock pulses, a logical "0" value associated with a blanking level of said at least one line of video data and located between said plurality of clock pulses, and a clock period associated with a frequency of said clock pulses.

12. The closed caption decoder as set forth in claim 11 wherein said second processor further comprises:

means for detecting a start bit associated with said closed caption data, said start bit having an amplitude greater than said logical "1" value.

13. The closed caption decoder as set forth in claim 12 wherein said second processor further comprises:

means for translating said intensity data into said first and second ASCII characters, wherein said translating means reads selected intensity data at a plurality of intervals after said start bit, each one of said plurality of intervals being a multiple of said clock period, and compares said selected intensity data to said logical "1" value and said logical "0" value.

14. The closed caption decoder as set forth in claim 13 wherein said second processor further comprises:

means for displaying at least one of said ASCII characters in said window.

15. The closed caption decoder as set forth in claim 13 wherein said second processor further comprises:

means for determining if said first ASCII character is a printable character or a control character.

16. The closed caption decoder as set forth in claim 13 wherein said second processor further comprises:

means for checking the parity of said first and second ASCII characters.

17. A method of capturing closed caption data from a television signal and displaying said closed caption data in a window of user-defined size and location on a screen of a video monitor, the method comprising:

capturing a line of video data containing the closed caption data from a frame of the television signal;

storing only a portion of the captured line of video data in a frame buffer as a plurality of pixel data, the pixel data comprising intensity data and color data; and

translating the pixel data stored in the frame buffer into two ASCII characters.

18. The method as set forth in claim 17 wherein the step of capturing decimates the line of video data by storing only every other pair of pixel data contained in the line of video data.

19. The method as set forth in claim 17 wherein the step of translating comprises the substeps of:

detecting a plurality of clock pulses contained in the intensity data of the line of video data; and

determining a logical "1" value associated with a peak amplitude of the plurality of clock pulses, a logical "0" value associated with a blanking level of the line of video data and located between the plurality of clock pulses, and a clock period associated with a frequency of the clock pulses.

20. The method as set forth in claim 19 wherein the step of translating comprises the substeps of:

detecting a start bit contained in the intensity data, the start bit being associated with the closed caption data and having an amplitude greater than the logical "1" value.

21. The method as set forth in claim 20 wherein the step of translating comprises the substeps of:

sampling the intensity data at a plurality of intervals after the start bit, each of the plurality of intervals being a multiple of the clock period;

comparing the sampled intensity data to the logical "1" value and the logical "0" value; and

translating the results of the step of comparing the sampled intensity data into a first ASCII character and a second ASCII character.

22. The method as set forth in claim 21 including the further step of displaying at least one of the ASCII characters in the window.