Glyph Adjustment in High Resolution Raster While Rendering

• US 20070188497A1
• Filed: 08/15/2006
• Published: 08/16/2007
• Est. Priority Date: 03/31/2004
• Status: Active Grant

• Current Assignee: Adobe Inc.
• Original Assignee: Adobe Systems Incorporated (Adobe Inc.)
• Inventors: Arnold, R., Dowling, Terence
• Granted Patent: US 7,719,536 B2
• Time in Patent Office: Days
• US Class Current: 345/469
• CPC Class Codes: G06T 11/203 Drawing of straight lines or curves
• CPC Class Codes: G09G 2340/0457 Improvement of perceived resolution by subpixel rendering
• CPC Class Codes: G09G 2340/10 Mixing of images, i.e. displayed pixel being the result of an operation, e.g. adding, on the corresponding input pixels
• CPC Class Codes: G09G 5/24 Generation of individual character patterns
• CPC Class Codes: G09G 5/28 for enhancement of character form, e.g. smoothing

Abstract

Methods and apparatus, including computer program products, that implement a method for glyph adjustment in high resolution raster while rendering. In one aspect, a method includes the actions of receiving a glyph for display at a size on a raster output device; receiving a grid ratio specifying an integer number of fine pixels of a high resolution grid that correspond to a device pixel of the output device; rendering the glyph at the size on the high resolution grid; determining for each line of pixels of the high resolution grid, a line-specific, per-transition adjustment number; and in each line of pixels, marking or erasing the line-specific, per-transition adjustment number of fine pixels in the high resolution grid at each transition from a marked fine pixel to an unmarked fine pixel in a particular direction of the line of pixels.

Claims

1. A method comprising:

receiving a glyph for display at a size on a raster output device;

receiving a grid ratio, the grid ratio specifying an integer number of fine pixels of a high resolution grid that correspond to a device pixel of a raster of the output device;

rendering the glyph at the size on the high resolution grid, the high resolution grid including fine pixels marked to represent the glyph and fine pixels that are unmarked;

determining for each line of pixels of the high resolution grid, a line-specific, per-transition adjustment number; and

in each line of pixels of the high resolution grid, marking or erasing the line-specific, per-transition adjustment number of fine pixels in the high resolution grid at each transition from a marked fine pixel to an unmarked fine pixel in a particular direction of the line of pixels.

2. The method of claim 1, wherein the glyph is associated with a font, and wherein determining the line-specific, per-transition adjustment number includes:

obtaining a standard stem width of the font;

calculating a scaled stem width for the glyph by scaling the standard stem width to the size at which the glyph is to be displayed on the raster output device;

calculating an adjustment number from the scaled stem width; and

determining an integer line-specific, per-transition adjustment number, the determining being based at least on the adjustment number.

3. The method of claim 2, wherein determining the integer line-specific, per-transition adjustment number includes:

defining a pattern of the adjustment number of fine pixels for distribution among lines of fine pixels of the high resolution grid; and

using the pattern to select, for each line of fine pixels in the high resolution grid, the integer number of fine pixels to be marked or erased at each transition from a marked fine pixel to an unmarked fine pixel in a particular direction.

4. The method of claim 3, wherein:

the pattern is a form of dithering in which the line-specific, per-transition adjustment number does not vary by more than one fine pixel from one line of fine pixels to a next line of fine pixels.

5. The method of claim 2, wherein:

the calculating of the adjustment number is based on one of a function for providing synthetic bold, a function for providing synthetic light, or a function providing optical compensation.

6. The method of claim 5, wherein:

the function for providing synthetic bold and the function for providing synthetic light each defines a linear relationship between adjustment number and scaled stem width; and

the function for optical compensation defines an inversely proportional relationship between adjustment number and scaled stem width.

7. The method of claim 2, wherein calculating an adjustment number includes:

calculating a component for producing a synthetic bold appearance or a synthetic light appearance;

calculating a component for optical compensation, the calculating of the component for optical compensation accounting for the component for producing a bold appearance or the component for producing the synthetic light; and

combining the components.

8. The method of claim 2, wherein the grid ratio specifies a number of rows of fine pixels that correspond to a height of the device pixel, wherein the line of fine pixels is a row in the high resolution grid, and wherein the adjustment number determined based on the scaled stem width is a first adjustment number, the method further comprising:

calculating a second adjustment number by dividing the first adjustment number by the number of rows of fine pixels corresponding to the height of the device pixel;

when the second adjustment number is not an integer, selecting two integers that delimit the second adjustment number;

defining a pattern of a number of instances of the two integers, a sum of values of the instances in the pattern equaling the first adjustment number, the number of instances equaling the number of rows of fine pixels corresponding to the height of the device pixel; and

selecting, based on the pattern, one of the two integers as the line-specific, per-transition adjustment number.

9. The method of claim 1, wherein obtaining the integer number includes:

calculating an adjustment number from the size at which the glyph is to be displayed, wherein size is expressed as either points per em or pixels per em; and

determining the line-specific, per-transition adjustment number, the determining being based at least on the adjustment number.

10. The method of claim 1, wherein:

the high resolution grid is stored in a digital memory as a bitmap.

11. The method of claim 10, wherein rendering the glyph includes:

adding unmarked fine pixels to an edge of the bitmap to allow for the marking or erasing.

12. The method of claim 10, further comprising:

adjusting a bitmap metric after the marking or erasing.

13. The method of claim 1, wherein:

the marking or erasing are performed by a rasterizer during rendering, the rasterizer being is a first component of a renderer.

14. The method of claim 13, further comprising:

downsampling the bitmap representing the adjusted version of the glyph.

15. The method of claim 13, wherein:

the downsampling is performed by a downsampler that is a second component of the renderer.

16. A computer-program product, tangibly stored on machine-readable medium, the product comprising instructions operable to cause a computing device to perform a method comprising:

receiving a glyph for display at a size on a raster output device;

receiving a grid ratio, the grid ratio specifying an integer number of fine pixels of a high resolution grid that correspond to a device pixel of a raster of the output device;

rendering the glyph at the size on the high resolution grid, the high resolution grid including fine pixels marked to represent the glyph and fine pixels that are unmarked;

determining for each line of pixels of the high resolution grid, a line-specific, per-transition adjustment number; and

in each line of pixels of the high resolution grid, marking or erasing the line-specific, per-transition adjustment number of fine pixels in the high resolution grid at each transition from a marked fine pixel to an unmarked fine pixel in a particular direction of the line of pixels.

17. The product of claim 16, wherein the glyph is associated with a font, and wherein determining the line-specific, per-transition adjustment number includes:

obtaining a standard stem width of the font;

calculating a scaled stem width for the glyph by scaling the standard stem width to the size at which the glyph is to be displayed on the raster output device;

calculating an adjustment number from the scaled stem width; and

determining an integer line-specific, per-transition adjustment number, the determining being based at least on the adjustment number.

18. The product of claim 17, wherein determining the integer line-specific, per-transition adjustment number includes:

defining a pattern of the adjustment number of fine pixels for distribution among lines of fine pixels of the high resolution grid; and

using the pattern to select, for each line of fine pixels in the high resolution grid, the integer number of fine pixels to be marked or erased at each transition from a marked fine pixel to an unmarked fine pixel in a particular direction.

19. The product of claim 18, wherein:

the pattern is a form of dithering in which the line-specific, per-transition adjustment number does not vary by more than one fine pixel from one line of fine pixels to a next line of fine pixels.

20. The product of claim 17, wherein:

the calculating of the adjustment number is based on one of a function for providing synthetic bold, a function for providing synthetic light, or a function providing optical compensation.

21. The product of claim 20, wherein:

the function for providing synthetic bold and the function for providing synthetic light each defines a linear relationship between adjustment number and scaled stem width; and

the function for optical compensation defines an inversely proportional relationship between adjustment number and scaled stem width.

22. The product of claim 17, wherein calculating an adjustment number includes:

calculating a component for producing a synthetic bold appearance or a synthetic light appearance;

calculating a component for optical compensation, the calculating of the component for optical compensation accounting for the component for producing a bold appearance or the component for producing the synthetic light; and

combining the components.

23. The product of claim 17, wherein the grid ratio specifies a number of rows of fine pixels that correspond to a height of the device pixel, wherein the line of fine pixels is a row in the high resolution grid, wherein the adjustment number determined based on the scaled stem width is a first adjustment number, and wherein the method further comprises:

calculating a second adjustment number by dividing the first adjustment number by the number of rows of fine pixels corresponding to the height of the device pixel;

when the second adjustment number is not an integer, selecting two integers that delimit the second adjustment number;

defining a pattern of a number of instances of the two integers, a sum of values of the instances in the pattern equaling the first adjustment number, the number of instances equaling the number of rows of fine pixels corresponding to the height of the device pixel; and

selecting, based on the pattern, one of the two integers as the line-specific, per-transition adjustment number.

24. The product of claim 16, wherein obtaining the integer number includes:

calculating an adjustment number from the size at which the glyph is to be displayed, wherein size is expressed as either points per em or pixels per em; and

determining the line-specific, per-transition adjustment number, the determining being based at least on the adjustment number.

25. The product of claim 16, wherein:

the high resolution grid is stored in a digital memory as a bitmap.

26. The product of claim 25, wherein rendering the glyph includes:

adding unmarked fine pixels to an edge of the bitmap to allow for the marking or erasing.

27. The product of claim 25, wherein the method further comprises:

adjusting a bitmap metric after the marking or erasing.

28. The product of claim 16, wherein:

the marking or erasing are performed by a rasterizer during rendering, the rasterizer being is a first component of a rendering engine.

29. The product of claim 28, wherein the method further comprises:

downsampling the bitmap representing the adjusted version of the glyph.

30. The product of claim 28, wherein:

the downsampling is performed by a downsampler that is a second component of the rendering engine.