Method for setting caption window attributes and associated television system

1. A method for setting caption window attributes for use in a television system having a palette, comprising steps of:

providing a plurality of attributive bit sets corresponding to a plurality of pixels in a caption;

comparing the attributive bit sets by utilizing a window condition in response to a setting caption window command for changing window color to a destination color-change value, so as to selectively update partial bits of the attributive bit sets to the color-change target value in response to the window condition; and

displaying a plurality of color values of the pixels according to the updated attributive bit sets and the palette;

wherein each of the pixels in the caption includes three targets namely a foreground index, a background index and a window color index; the palette includes a foreground index table, and a background index table; and the window color index and the foreground index share the foreground index table.

2. The method for setting caption window attributes according to claim 1 , wherein the television system comprises a television controller and a dynamic random access memory (DRAM), the palette is stored in a static random access memory (SRAM) in the television controller, and the attributive bit sets in the caption are stored in the DRAM.

3. The method for setting caption window attributes according to claim 1 , wherein the caption includes m×n pixels, and a format of the attributive bit sets corresponding to the pixels is in a color index mode.

4. The method for setting caption window attributes according to claim 3 , wherein the color index mode uses 1 bit, 2 bits, 3 bits, 5 bits, and 5 bits to represent a color value format, alpha, blink, a foreground index, and a background index, respectively.

5. The method for setting caption window attributes according to claim 4 , wherein the window condition is asserted by setting 1 bit of the alpha's 2 bits.

6. The method for setting caption window attributes according to claim 1 , wherein the pixels in the caption have n targets, the palette has n−1 color indices, and two specific targets from the n targets share a same color index.

7. The method for setting caption window attributes according to claim 1 , wherein each of the pixels in the caption includes three targets namely a foreground index, a background index and a window color index; the palette includes a foreground index table and a background index table; and the window color index and the background index share the background index table.

8. The method for setting caption window attributes according to claim 7 , wherein partial bits of each of the attributive bit sets are filled in with the window color index or the background index.

9. The method for setting caption window attributes according to claim 8 , wherein the displaying step comprises steps of:

determining whether a foreground/background indicative bit denotes the foreground is to be used, and looking up a color value corresponding to the foreground index from the foreground index table; and

determining whether the foreground/background indicative bit denotes the background is to be used, and looking up a color value corresponding to the background index from the background index table.

10. The method for setting caption window attributes according to claim 1 , wherein selectively updating partial bits of each of the attributive bit sets are filled in with the window color index or the foreground index.

11. The method for setting caption window attributes according to claim 10 , wherein the displaying step comprises steps of:

determining whether a foreground/background indicative bit denotes the foreground is to be used, and looking up a color value corresponding to the foreground index from the foreground index table; and

determining whether the foreground/background indicative bit denotes the background is to be used, and looking up a color value corresponding to the background index from the background index table.

12. A television system for reducing caption memory, comprising:

a system memory, including a plurality of attributive bit sets corresponding to a plurality of pixels in a caption;

a television controller, built-in with an SRAM for storing a palette, coupled to the system memory, and for comparing the plurality of attributive bit sets in response to a setting caption window attribute command for changing window color to a destination color-change value, so as to selectively update partial bits of the attributive bit sets to the destination color-change value in response to a window condition, and output color values of the pixels corresponding to the attributive bit sets and the palette; and

a display panel, coupled to the television controller, and for receiving the color values for display;

wherein each of the pixels in the caption includes three targets namely a foreground index, a background index, and a window color index; the palette includes a foreground index table and a background index table; and the window color index and the back round index share the back round index table.

13. The television system according to claim 12 , wherein the system memory is a DRAM, the caption includes m×n pixels, a format of the attributive bit sets corresponding to the pixels is in a color index mode, and the color index mode uses 1 bit, 2 bits, 3 bits, 5 bits, and 5 bits to represent a color value format, alpha, blink, a foreground index, and a background index, respectively.

14. The television system according to claim 13 , wherein the window condition is asserted by setting 1 bit of the alpha's 2 bits.

15. The television system according to claim 12 , wherein the pixels in the caption has n targets, the palette has n−1 color indices, and two specific targets from the n targets share a same color index.

16. The television system according to claim 12 , wherein selectively updating partial bits of each of the attributive bit sets are filled in with the window color index or the background index.

17. The television system according to claim 12 , comprising:

a micro processing unit, for receiving a window color-change command and parsing the destination color-change value from the command;

a graphic output processor, for fetching the attributive bit sets stored in the system memory for video output; and

a graphic engine, coupled to the micro processing unit and the graphic output processor, for producing the attributive bit sets to be displayed in the caption on the screen, comparing the attributive bit sets in the system memory in response to the destination color-change value from the micro processing unit, updating the partial bits of the partial attributive bit sets to the destination color-change value in response to the window condition, and utilizing the corresponding attributive bit sets and palette to provide color values of the pixels in the caption to the graphic output processor for output.