Hinted stem placement on high-resolution pixel grid

A system for rendering a character for display in grayscale on a grayscale output device, comprising:

• means for defining a coarse grid of cells, each coarse cell corresponding to an output device grayscale pixel, and a high-resolution grid of fine cells, the high-resolution grid being aligned with said coarse grid so that each coarse cell includes an integer number of undivided fine cells;
• means for placing a character defined by a font program with reference to the coarse grid and fine grid, the character having a stem hinted with two parallel edges that is placed with reference to the grids when the character is so placed, the stem hint edges being separated by a stem width;
• and
• stem aligner means for processing the stem before rendering the character for output on the output device, the stem aligner means comprising means for performing an unbiased-stems hinted stem placement policy, wherein the unbiased-stems policy considers stem spread when determining stem placement.

A method for processing a stem of a character outline, comprising:

• in one or more computers performing operations comprising:
• selecting a hinted stem placement policy from a set of policies comprising at least either a black-edge policy or an unbiased-stems policy, where a black edge policy considers stem width when determining stem placement and an unbiased-stems policy considers stem spread when determining stem placement;
• placing a character defined by a font program with reference to a coarse grid and an overlapping fine grid, the character having a stem hinted with two parallel edges that is placed with reference to the grids when the character is so placed, the stem hint edges being separated by a stem width;
• and
• processing the stem before rendering the character for output on the output device in accordance with the selected policy,
• wherein, processing the stem in accordance with the black-edge policy includes:
• rounding the stem width to the width of an integral number of fine cells;
• determining the stem width;
• and
• if the stem width is at least one coarse cell, moving the stem with rounded width a minimum distance so that at least one of the stem edges aligns with a parallel coarse cell edge.

A computer-readable medium encoded with a computer program product for rendering a character for display in grayscale on a grayscale output device, the product comprising instructions operable to cause a programmable processor to:

• define a coarse grid of cells, each coarse cell corresponding to an output device grayscale pixel, and a high-resolution grid of fine cells, the high-resolution grid being aligned with said coarse grid so that each coarse cell includes an integer number of undivided fine cells, the grids defining edges of the cells;
• place a character defined by a font program with reference to the coarse grid and fine grid, the character having a stem hinted with two parallel edges that are placed with reference to the grids when the character is so placed, the stem hint edges being separated by a stem width;
• and
• perform a black-edge hinted stem placement policy, wherein instructions to perform a black-edge hinted stem placement policy comprise instructions to:
• round the stem width to the width of an integral number of fine cells;
• determine the stem width;
• and
• if the stem width is at least one coarse cell, move the stem with rounded width a minimum distance so that at least one of the stem hint edges aligns with a parallel coarse cell edge.

A computer-readable medium encoded with a computer program product for rendering a character for display in grayscale on a grayscale output device, the product comprising instructions operable to cause a programmable processor to:

• define a coarse grid of cells, each coarse cell corresponding to an output device grayscale pixel, and a high-resolution grid of fine cells, the high-resolution grid being aligned with said coarse grid so that each coarse cell includes an integer number of undivided fine cells, the grids defining edges of the cells;
• place a character defined by a font program with reference to the coarse grid and fine grid, the character having a stem hinted with two parallel edges that are placed with reference to the grids when the character is so placed, the stem hint edges being separated by a stem width;
• and
• perform an unbiased-stems hinted stem placement policy, wherein the unbiased-stems policy considers stem spread when determining stem placement.

A computer-readable medium encoded with a computer program product for processing a stem of a character outline, the product comprising instructions operable to cause a programmable processor to:

• select a hinted stem placement policy from a set of policies comprising at least either a black-edge policy or an unbiased-stems policy, where a black-edge policy considers stem width when determining stem placement and an unbiased-stems policy considers stem spread when determining stem placement;
• place a character defined by a font program with reference to a coarse grid and an overlapping fine grid, the character having a stem hinted with two parallel edges that is placed with reference to the grids when the character is so placed, the stem hint edges being separated by a stem width;
• and
• process the stem before rendering the character for output on an output device in accordance with the selected policy,
• wherein, instructions to process the stem in accordance with a black-edge policy, include instructions to:
• round the stem width to the width of an integral number of fine cells;
• determine the stem width;
• and
• if the stem width is at least one coarse cell, move the stem with rounded width a minimum distance so that at least one of the stem edges aligns with a parallel coarse cell edge.

A method for rendering a character for display in grayscale on a grayscale output device, comprising:

• in one or more computers performing operations comprising:
• defining a coarse grid of cells, each coarse cell corresponding to an output device grayscale pixel, and a high-resolution grid of fine cells, the high-resolution grid being aligned with said coarse grid so that each coarse cell includes an integer number of undivided fine cells;
• placing a character defined by a font program with reference to the coarse grid and fine grid, the character having a stem hinted with two parallel edges that is placed with reference to the grids when the character is so placed, the stem hint edges being separated by a stem width;
• and
• processing the stem before rendering the character for output on the output device including performing an unbiased-stems hinted stem placement policy, wherein the unbiased-stems policy considers stem spread when determining stem placement.

A method for rendering a character for display in grayscale on a grayscale output device, comprising:

• in one or more computers performing operations comprising:
• defining a coarse grid of cells, each coarse cell corresponding to an output device grayscale pixel, and a high-resolution grid of fine cells, the high-resolution grid being aligned with said coarse grid so that each coarse cell includes an integer number of undivided fine cells, the grids defining edges of the cells;
• placing a character defined by a font program with reference to the coarse grid and fine grid, the character having a stem hinted with two parallel edges that are placed with reference to the grids when the character is so placed, the stem hint edges being separated by a stem width;
• and
• processing the stem before rendering the character for output on the output device, including performing a black-edge hinted stem placement policy, wherein performing a black-edge policy comprises:
• rounding the stem width to the width of an integral number of fine cells;
• determining the stem width;
• and
• if the stem width is at least one coarse cell, moving the stem with rounded width a minimum distance so that at least one of the stem hint edges aligns with a parallel coarse cell edge.