Generation of glow effect

1. A method for generating a glow effect in an image, comprising:

selecting an area within a rendered scene that is to glow to produce a selected area image based on a determination of luminance of scene elements in the scene;

generating glow by blurring the selected area image to produce a glowing area image; and

adding the glowing area image to the scene to provide the glow effect,

wherein the selecting comprises:

rendering the scene to provide a rendered scene image;

creating a mask that defines the area which is to glow; and

applying the mask to the rendered scene image to produce the selected area image.

2. A method according to claim 1 , wherein the creating of the mask comprises:

creating stencil values within a stencil buffer that define the area which is to glow, wherein the stencil values correspond to respective scene elements within the rendered scene image.

3. A method according to claim 2 , wherein the creating of the stencil values comprises:

setting the stencil values to an initial value before the scene is rendered; and

modifying selected initial values in the course of the rendering to provide the stencil values that define the area which is to glow.

4. A method according to claim 2 , wherein the applying comprises:

providing luminance values respectively associated with the scene elements within the rendered scene image;

performing a masking test by comparing the stencil values in the stencil buffer with corresponding luminance values associated with respective scene elements in the rendered scene image;

outputting a masking color value for scene elements in the rendered scene image that fail the masking test; and

outputting a non-masking color value for scene elements in the rendered scene image that pass the masking test.

5. A method as recited in claim 4 , wherein the masking test determines whether luminance values associated with the respective scene elements in the rendered scene image are larger than corresponding stencil values in the stencil buffer.

6. A method as recited in claim 4 , wherein the masking color is black, and the non-masking color is a non-black color.

7. A method as recited in claim 1 , wherein the selected area image has a smaller information content size than the rendered area image.

8. A method as recited in claim 1 , wherein the generating comprises:

generating multiple versions of the selected area image; and

forming a weighted sum of the multiple versions to provide the glowing area image.

9. A method as recited in claim 8 , where the multiple versions are offset from a reference center point in different respective directions.

10. A method according to claim 9 , wherein the multiple versions include a first collection of versions that are offset from the reference center point by a first prescribed amount in different respective directions, and a second collection of versions that are offset from the reference center point by a second prescribed amount in different respective directions.

11. A method as recited in claim 1 , wherein the glowing area image has a smaller information content size than the selected area image.

12. A method as recited in claim 1 , wherein the selecting comprises rendering the scene to provided a rendered scene image, and wherein the adding comprises adding color values within the glowing area image to associated color values within the rendered scene image.

13. A method according to claim 1 , wherein the selecting comprises:

rendering the scene to provided a rendered scene image; and

separately rendering the area which is to glow to produce the selected area image.

14. A method according to claim 1 , wherein the selecting comprises selecting an element of the selected area image if the element has a luminance which exceeds a prescribed threshold luminance.

15. A computer-readable medium having computer-executable instructions for performing the method recited in claim 1 .

16. An apparatus for generating a glow effect in an image, comprising:

area formation logic configured to select an area within a rendered scene that is to glow to produce a selected area image based on a determination of luminance of scene elements in the scene, wherein selection by the selection logic comprises: rendering the scene to provide a rendered scene image, creating a mask that defines the area which is to glow, and applying the mask to the rendered scene image to produce the selected area image;

glow generation logic configured to generate glow using the selected area image to produce a glowing area image; and

glow application logic configured to add the glowing area image to the scene to provide the glow effect.

17. The apparatus of claim 16 , wherein the area formation logic is configured to select an element of the selected area image if the element has a luminance which exceeds a prescribed threshold luminance.