Methods and apparatus for rendering an image with depth-of-field display

1. A rendering apparatus for showing depth of field in an image, comprising:

(a) a Z buffer operable to establish a depth value of objects in an image;

(b) an image generator unit to generate an image in a just-in-focus state while writing a Z value of each of dots in the image into the Z buffer;

(c) a blurring unit operable to produce a blurred image of the image in the just-in-focus state; and

(d) an overwriting unit operable to selectively overwrite portions of the blurred image on the image in the just-in-focus state by comparing a preset Z value to the Z value of each of the dots in the Z buffer.

2. A rendering apparatus as claimed in claim 1 , wherein the preset Z value is changed arbitrarily and continuously with time such that an image field of the objects that are in the just-in-focus state is correspondingly changed.

3. A rendering apparatus as claimed in claim 1 , wherein the blurring unit is operable to produce reduced images and to magnify the reduced images to generate out-of-focus images.

4. A rendering apparatus as claimed in claim 3 , wherein the blurring unit uses a pixel-interpolation algorithm to produce the reduced images.

5. A rendering apparatus as claimed in claim 4 , wherein the pixel-interpolation algorithm comprises a bilinear filter algorithm.

6. A rendering apparatus as claimed in claim 1 , wherein the overwriting unit is operable to selectively mask objects corresponding to the preset Z value and to overwrite all un-masked objects with corresponding ones of the out-of-focus images such that objects located farther and nearer than the preset Z value are out of focus.

7. A rendering apparatus as claimed in claim 1 , further comprising a video random access memory (VRAM) having a rendering area and a texture area, wherein the blurring unit is operable to produce sequentially reduced images in the VRAM and to magnify the reduced images to generate a plurality of different levels of out-of-focus images.

8. A method for showing depth of field in an image, comprising:

(a) establishing a depth value of objects in an image;

(b) generating an image in a just-in-focus state while writing a Z value of each of dots in the image into a Z buffer;

(c) producing a blurred image of the image in the just-in-focus state; and

(d) selectively overwriting portions of the blurred image on the image in the just-in-focus state by comparing a preset Z value to the Z value of each of the dots in the Z buffer.

9. A method as claimed in claim 8 , wherein the preset Z value is changed arbitrarily and continuously with time such that an image field of the objects that are in the just-in-focus state is correspondingly changed.

10. A method as claimed in claim 8 wherein the blurred image is produced by reduced images and magnifying the reduced images to generate out-of-focus images.

11. A method as claimed in claim 10 , further comprising using a pixel-interpolation algorithm to produce the reduced images.

12. A method as claimed in claim 11 , wherein the pixel-interpolation algorithm comprises a bilinear filter algorithm.

13. A method as claimed in claim 8 , objects are selectively masked corresponding to the preset Z value and all un-masked objects are overwritten with corresponding ones of the out-of-focus images such that objects located farther and nearer than the preset Z value are out of focus.

14. A method as claimed in claim 8 , wherein the blurring is executed in a video random access memory (VRAM) having a rendering area and a texture area, including producing sequentially reduced images in the VRAM and magnifying the reduced images to generate a plurality of different levels of out-of-focus images.

15. A storage medium for storing an image-generating program capable of execution by a microprocessor to perform steps for showing depth of field in an image, the steps comprising:

(a) establishing a depth value of objects in an image;

(b) generating an image in a just-in-focus state while writing a Z value of each of dots in the image into a Z buffer;

(c) producing a blurred image of the image in the just-in-focus state; and

(d) selectively overwriting portions of the blurred image on the image in the just-in-focus state by comparing a preset Z value to the Z value of each of the dots in the Z buffer.

16. A storage medium as claimed in claim 15 , further comprising the step of arbitrarily and continuously changing the preset Z value with time such that an image field of the objects that are in the just-in-focus state is correspondingly changed.

17. A storage medium as claimed in claim 15 , wherein the step of producing a blurred image produces reduced images and magnifies the reduced images to generate out-of-focus images.

18. A storage medium claimed in claim 17 , wherein the step of producing a blurred image uses a pixel-interpolation algorithm to produce the reduced images.

19. A storage medium as claimed in claim 18 , wherein the pixel-interpolation algorithm comprises a bilinear filter algorithm.

20. A storage medium as claimed in claim 15 , wherein the step of selectively overwriting selectively masks objects corresponding to the preset Z value and overwrites all un-masked objects with corresponding ones of the out-of-focus images such that objects located farther and nearer than the preset Z value are out of focus.

21. A storage medium as claimed in claim 15 , wherein the step of blurring is executed in a video random access memory (VRAM) having a rendering area and a texture area, including producing sequentially reduced images in the VRAM and magnifying the reduced images to generate a plurality of different levels of out-of-focus images.