Techniques for displaying complex characters

• US 6,262,708 B1
• Filed: 06/16/1999
• Issued: 07/17/2001
• Est. Priority Date: 06/16/1999
• Status: Expired due to Term

• Current Assignee: Sun Microsystems Incorporated (Oracle Corporation)
• Original Assignee: Sun Microsystems Incorporated (Oracle Corporation)
• Inventors: Chu, Sing Yun
• Primary Examiner(s): Brier, Jeffery
• Assistant Examiner(s): HAVAN, THU THAO
• Application Number:
  US09/334,781
• Time in Patent Office: 762 Days
• Field of Search: 345/127, 345/439, 345/429, 345/430, 345/141, 345/467, 345/471, 345/128, 345/129, 345/130, 345/472, 382/185, 382/183, 382/182, 382/298, 348/224, 348/226, 348/581, 348/468, 348/564, 725/37, 725/131, 725/139, 725/151
• US Class Current: 345/667
• CPC Class Codes: G09G 2320/0247 Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes
• CPC Class Codes: G09G 5/28 for enhancement of character form, e.g. smoothing
• CPC Class Codes: H04N 21/426 Internal components of the client ; Characteristics thereof H04N5/44 takes precedence
• CPC Class Codes: H04N 5/44504 Circuit details of the additional information generator, e.g. details of the character or graphics signal generator, overlay mixing circuits

Abstract

Systems and methods for rendering a complex character suitable for display on a monitor are provided. A raw character bitmap representing the complex character is filtered to form a filtered bitmap so as to reduce the effects of monitor flicker and enhance image contrast. The filtered bitmap is then scaled down to a target bitmap using a bilinear scaling operation followed by recursive cubic scaling operations. The target bitmap is suitably sized for storage in a memory device coupled to the monitor.

Claims

1. A method for rendering an image of a complex character for display on a monitor, wherein the image is formed of a plurality of pixels arranged in rows and columns and is represented by a raw character bitmap, comprising:

filtering the raw character bitmap to form a filtered character bitmap performing a first type scaling operation on the filtered bitmap to form a first scaled bitmap;

determining a scalefactor based upon the first scaled bitmap and a target bitmap, wherein the target bitmap is suitable for storage in a memory device coupled to the monitor; and

further recursively scaling the first scaled bitmap using a second type scaling operation to form the target bitmap based upon the scalefactor.

2. A method as recited in claim 1, wherein the first type scaling operation is a bilinear scaling operation.

3. A method as recited in claim 2, wherein the second type scaling operation is a cubic scaling operation.

4. A method as recited in claim 3, wherein the filtering further comprises:

multiplying the raw bitmap with a gaussian filter having a gaussian kernal to form a multiplied bitmap; and

dividing the multiplied bitmap by a reduced kernal divisor to form the filtered bitmap, wherein the dividing by the reduced divisor increases the contrast between the darkest pixel and the brightest pixel of the filtered bitmap.

5. A method as recited in claim 4, wherein the reduced kernal divisor is the sum of the kernal reduced by a contrast enhancement factor, wherein the sum of the kernal is the summation of the elements of the kernal.

6. A method as recited in claim 5, wherein the kernal is a 5×

5 gaussian kernal.

7. A method as recited in claim 1, wherein the monitor is coupled to a television system suitable for receiving television signals.

8. A method as recited in claim 7, wherein the television system is coupled to a set top box arranged to retrieve a requested document from a host computer, wherein the requested document includes the raw character bitmap.

9. A method as recited in claim 8, wherein the set top box includes a cache memory suitable for storing the target bitmap.

10. A method as recited in claim 9, wherein the cache memory is a Read Only Memory device arranged to store a plurality of provided target bitmaps each corresponding to a particular complex character.

11. An apparatus for rendering an image of a complex character for display on a monitor, wherein the image is formed of a plurality of pixels arranged in rows and columns, and wherein the complex character is represented by a raw character bitmap, comprising:

a filtering unit that receives the raw character bitmap and performs a selected filtering operation to form a filtered character bitmap;

a decimator unit coupled to the filtering unit that receives the filtered character bitmap and performs a series of multiple type scaling operations on the received filtered character bitmap to form a target bitmap, wherein the target bitmap is representative of a selected font size corresponding to the displayed image; and

a memory device coupled to the decimator unit arranged to store the target bitmap, wherein when a complex character corresponding to a selected one of the target bitmaps is to be displayed on the television monitor, the selected bitmap is passed to a frame buffer unit coupled to cache memory device.

12. An apparatus as recited in claim 11, wherein the filtering operation comprises:

multiplying the raw character bitmap with a gaussian filter having a kernal to form a multiplied bitmap; and

dividing the multiplied bitmap by a reduced kernal divisor to form the filtered bitmap such that the contrast between the darkest pixel and the brightest pixel of the filtered bitmap is enhanced.

13. A method as recited in claim 12, wherein the reduced kernal divisor is the sum of the kernal reduced by a contrast enhancement factor, wherein the sum of the kernal is the summation of the elements of the kernal.

14. A method as recited in claim 13, wherein the kernal is a 5×

5 gaussian kernal.

15. An apparatus as recited in claim 11, wherein the performs a series of multiple type scaling operations on the received filtered character bitmap to form a target bitmap comprises:

performing a first type scaling operation on the filtered character bitmap to form a first scaled character bitmap;

determining a scalefactor based upon the first scaled character bitmap and the target bitmap; and

further recursively scaling the first scaled bitmap using a second type scaling operation to form the target bitmap, wherein the recursion is based upon the scalefactor.

16. An apparatus as recited in claim 15, wherein the first type scaling operation is a bilinear scaling operation and wherein the second type scaling operation is a cubic scaling operation.

17. An apparatus as recited in claim 16, wherein the apparatus is a set top box coupled to a television arranged to retrieve a selected document from a host computer connected thereto.

18. An apparatus as recited in claim 17, wherein the host computer is part of a computer network.

19. An apparatus as recited in claim 18, wherein the computer network is the Internet and the requested document is an HTML document.

20. A set top box as recited in claim 11, wherein the memory device is a Read Only Memory device arranged to store the target bitmaps corresponding to the complex characters.