Adobe, Inc.

R David Arnold

Terence S Dowling

Zhihong Ding

Eric Muller

Judy S Lee

Timothy Wojtaszek

The visual similarity between fonts is determined using visual descriptors of character images in the fonts. A model used to generate the visual descriptors may include a set of letterforms, keypoint locations on each letterform, and detail shapes at zero, one, or more detail areas on the letterform. In some instances, the model may also set forth one or more geometric measurements. Based on the model, a visual descriptor may be generated for a character image from a font by identifying a letterform of the character image, identifying keypoint locations on the character image, and identifying a detail shape at any detail areas on the character image. Additionally, the visual descriptor may include any geometric measurement defined by the model. The visual similarity between two fonts may be determined as a function of the differences between pairs of visual descriptors for the fonts that correspond with the same letterform.

Automatic measure of visual similarity between fonts

Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for modifying glyphs. In one aspect, a method includes receiving a glyph outline for a glyph to be rendered, the glyph to be rendered being associated with a character of a particular font and at a specified scaled size, the glyph to be rendered having one or more horizontal stems; identifying a darkening amount to be applied to the one or more horizontal stems of the glyph; modifying hints of the one or more horizontal stems of the glyph outline using the identified darkening amount to modify the glyph outline; and rasterizing the glyph using the modified glyph outline.

Modifying glyph outlines

Methods and apparatus implementing and using techniques for scaling a character having stems. A character including stems and having an associated output resolution and an associated bit depth can be received. The counters defined by the stems can be grouped into one or more chains of counters. The stems of the character can be aligned based on a stem alignment policy while the chains of counters are balanced based on the output resolution. A pixel map can be created at the output resolution and the output bit depth based on the aligned stems.

Course grid aligned counters

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.

Glyph adjustment in high resolution raster while rendering

Methods and apparatus, including computer program products, that implement a method for determining a winding order for a glyph associated with a font. The glyph has an outline that has an outside path. In one aspect, a method includes identifying four extrema points of the outline, each being an intersection of two vectors obtained from the outline; and for each of the points, calculating a cross product of the two vectors intersecting at the point. A positive result indicates that the outside path is wound in a first direction, and a negative result indicates that the outside path is wound in an opposite, second direction. The winding order of the outside path is determined based on the cross products calculated. In a particular implementation, the method determines that the outside path is wound counter clockwise when three or four of the results are positive.

Winding order test for digital fonts

Methods and apparatus, including computer program products, implementing and using techniques for rendering a glyph to make it more readable. In an implementation, a glyph associated with a font to be rendered at a size is received, and a set of initial density values is calculated to provide one density value for each of a set of device pixels to represent the glyph. An initial adjustment value is calculated for the glyph. For one or more of the device pixels in the set of device pixels, a length of an edge of the glyph that passes through the device pixel is calculated. For one or more of the device pixels, the initial density value is adjusted by a final adjustment value, the final adjustment value based upon the initial adjustment value and the length of the edge of the glyph passing through the device pixel.

Edge detection based stroke adjustment

Methods and apparatus implementing a technique for rendering a hinted character for display in grayscale on a grayscale output device in accordance with a hinted stem placement policy. In one embodiment, the policy is a black-edge policy, by which a hinted stem is moved so that at least one of the hinted stem edges aligns with an edge of a device cell (which corresponds to an output device pixel). In another embodiment, the policy is an unbiased-stems policy, by which a hinted stem is moved a minimum distance to have it span a minimum number of device cells.

Hinted stem placement on high-resolution pixel grid

Methods and apparatus, including computer program products, that implement a method for adjusting a glyph outline while rendering. In one aspect a method includes receiving a glyph to be rendered at a size; generating from the glyph an outline of line segments, each line segment having two endpoints; translating the line segments all in an outward or inward direction, each line segment being moved by a distance and then rejoining pairs of adjacent line segments by extending or trimming their endpoints until each pair of adjacent line segments join at an intersection point that is an endpoint of each the line segments of the pair; and determining an augmented scaled outline of the glyph from the translated and rejoined line segments.

Glyph outline adjustment while rendering

Methods and apparatus implementing and using techniques for rendering a stroke (e.g., a line or glyph). An initial adjustment value can be calculated for the stroke, and an offset amount calculated based on the initial adjustment value, such that a minimum number of device pixels will be marked by the stroke after adjusting density values of device pixels representing the stroke. A high resolution representation of the stroke (e.g., a set of device pixels each having an initial density value) is rendered so that one or more edges of the stroke is offset from a device resolution grid by the offset amount. A length of an edge of the stroke that passes through a device pixel can be calculated, and the density value of the device pixel adjusted by a final adjustment value based on the initial adjustment value and the length of the edge of the stroke.

Adjusted Stroke Rendering

Adjusted stroke rendering

Methods, apparatus, including computer program products, and systems implement and use techniques for rendering glyphs. A representation of a glyph is generated, the glyph to be rendered at a size on an output device having a device resolution. A bitmap representation of the glyph is generated using a first anti-aliasing process in a first direction and using a different second anti-aliasing process in a second direction.

Anisotropic anti-aliasing

Methods, apparatus, including computer program products, and systems implement and use techniques for rendering glyphs. A plurality of glyphs to be rendered are received. For each glyph, an anti-aliasing procedure is selected to render the glyph. The anti-aliasing procedure is selected from a first anti-aliasing procedure and one or more alternative anti-aliasing procedures. The anti-aliasing procedure for each glyph is selected based on the glyph.

Dynamic selection of anti-aliasing procedures

Methods, systems and apparatus for generating test patterns for selecting a transfer function of a display device. A method includes generating multiple simulated transfer functions for a display device, rendering multiple patterns of anti-aliased parallel lines on the display device, each pattern rendered according to a corresponding one of the simulated transfer functions and including off-vertical lines and off-horizontal lines, receiving an input from a user of the display device selecting one of the patterns rendered on the display device and setting a transfer function for the display device to the simulated transfer function representing the selected pattern, the transfer function characterizing a relationship between an applied input voltage and an output luminance for any given pixel on the display device.

Selecting a transfer function for a display device

A method and apparatus for processing a character for anti-aliased display on a raster output device. A set of density values is computed for a set of raster positions to represent the character and the density values of the set are scaled to extend their range upward toward a maximum density value, whereby generally at least one of the density values of the set becomes the maximum density value. In one embodiment, the set of density values is computed from a rendering of the character at resolution higher than the resolution of the output device. In another embodiment, the character is created by a font having font metrics including a reference dimension, and the density values are scaled by computing adjusted values as a non-decreasing function of the original values, the function being defined to compute a maximum adjusted density value for at least one non-maximum density value.

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Mountain View, CA, United States of America

R David Arnold