Reexamination Certificate
1996-02-09
2001-04-10
Jankus, Almis R. (Department: 2412)
Reexamination Certificate
active
06213653
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to the display of data by output devices, and more particularly to a method and apparatus for interpolating a higher resolution image from a lower resolution image to create a higher displayed visual quality of the image.
A computer system can output data to a wide variety of output display devices. Output display devices such as laser printers, plotters, and other printing devices produce an image on a sheet of paper or other physical surface or media, while output display devices such as computer monitors and flat-panel display devices develop visual representations on a computer screen.
Many output display devices receive display data in the form of a “bitmap” or “pixel map” and generate images from the display data. A pixel is a fundamental picture element of an image generated by an output display device, and a bitmap is a data structure including information concerning a number of pixels of the representation. Bitmaps that contain more than on/off information, such as color values, are often referred to as “pixel maps.” As used herein, both bitmaps and pixel maps are referred to as “bitmaps.” For example, a printer can print dots on a piece of paper corresponding to the information of a bitmap. Alternatively, a computer monitor can illuminate pixels based upon the information of the bitmap. The term “image” is used interchangeably with the term “bitmap” to refer to both the data that is provided to an output display device as well as the actual outputted visual representation displayed by the display device. A “raster” output device creates a visual representation by displaying the array of pixels arranged in rows and columns from the bitmap. Most output devices, other than plotters, are raster output devices.
Images are typically displayed with a number of different shades or colors assigned to each of the pixels of the image. Herein, the term “gray level” is used to refer to the particular shade, color, and/or brightness of a pixel. For example, an output display device that can display 256 “gray levels” might display 256 shades of gray, or, alternatively, 256 different colors or shades of colors. Many examples herein refer to gray levels between the extreme gray levels of black (or dark) at one end of the scale and white (or light) at the opposing end of the scale. The intermediate gray levels between these extremes are displayed as shades of gray or as different colors such as red, yellow, blue, etc., or shades of different colors. Images are also specified with a resolution. There are two types of resolution referred to herein: spatial resolution and “gray level” (or “tonal”) resolution. Spatial resolution refers to the number of pixels per unit dimension in an image, and is often expressed as dots per inch (dpi) or pixels per inch. Gray level resolution refers to the amount of different gray levels that can be displayed in an image; the greater the number of gray levels that can be displayed, the greater the gray level resolution.
Images can be specified with a bitmap depth or pixel depth, i.e., as an “n-bit” bitmap or “n-bit” image, which signifies how many gray levels can (potentially) be displayed in the image. The number of gray levels displayed is equal to 2
n
; for example, a 2-bit image allows the the output device to display 4 gray levels, a 4-bit image allows the output device to display 16 gray levels, etc. Some output display devices can display an individual pixel at one of multiple available gray levels. For example, a display device with pixel depth of 4 bits can display a pixel in one of 16 different available gray levels, while an 8-bit display device can display a pixel in one of 256 available gray levels. For instance, continuous tone (“contone”) output devices typically display 256 gray levels; sometimes, a 16 gray-level device is called a contone device. Other output display devices may only be able to display a pixel in one of 2 available gray levels, e.g., black or white. These “bi-level” or “halftone” display devices include some laser printers, ink jet printers, other black and white printers, monochrome monitors, image setters, color output devices having bi-level output for each color component, etc.
Output display devices also typically are able to display additional gray levels by adjusting the spatial density of pixels in “pixel clusters” (also called “halftone cells”). This process of displaying additional gray levels is known as “dithering” or “halftoning.” Dithering typically maps the pixels in the original image to available gray levels on the device. A pixel cluster is a group of one or more pixels that is repeated across an area to provide a simulated gray level, where at least two pixels in the pixel cluster are at different gray levels. For example, in a bi-level scheme having two gray levels, some of the pixels of the pixel cluster are displayed as black (dark), while other pixels in the cluster are white (light). By adjusting the number of pixels in the cluster that are black and white, different gray levels can be simulated (typically, contone devices do not use dithering). If the spatial resolution of the clusters is high enough, then a viewer will see the cluster as a shade of gray. For example, a circular dot pattern in each pixel cluster is commonly used in print devices, where the dot is made larger or smaller for each gray level to be represented. Or, a checkerboard pattern of black and white pixels can be used, where black and white pixels are alternated in the pixel cluster such that no pixel is adjacent to a pixel having the same gray level within the cluster. These patterns are often used to provide an intermediate gray level between extreme black and white gray levels. The number of black pixels in the cluster can be increased to create a darker gray level, and the number of white pixels can be increased to create a lighter gray level.
An image often may be of poor visual quality. For example, an image may have a low spatial resolution, where the pixels of the image are relatively large and can be noticed by a human viewer of the image as “jagged” edges on lines and objects rather than as smooth edges. An image also may have a low gray level resolution, i.e., the image may only include a small number of gray levels and/or the output device may only be able to display a small number of gray levels. The viewer can thus notice undesired large transitions or contours between different pixel gray levels where a smooth transition of gray levels (i.e., a “blend”) may be desired.
An image may often be processed to increase the visual quality of the image. Image interpolation is one method by which the visual quality of an image can be increased.
FIG. 1
is a block diagram of a standard image interpolation process
10
. An original image
12
is input to an interpolation processor
14
implemented on a computer system. The interpolation processor
14
determines the resolution of the original image and the resolution of a primary target display device
16
which is to be used to display the image. An expansion factor
18
(or scale factor) is determined which is the multiplier by which the spatial resolution of the original image will be increased (if necessary) when displaying the image. The interpolation processor
14
applies the expansion factor in an interpolation process which produces an interpolated image
20
. The interpolated image is then provided to the target display device
16
to be displayed, or the interpolated image can be stored, processed, sent to a different display device, or otherwise manipulated. The interpolated image
20
is usually of higher spatial resolution and may, in some cases, also be of higher gray level resolution than the original image, and thus is generally of higher visual quality than the original image, i.e., the interpolated image looks “smoother” in both shape and color and is more realistic.
The process of interpolation is illustrated in greater detail with respect to
FIGS. 2
a
and
2
b.
FIG. 2
a
shows a pi
Borg Lars U.
Iyer Shankar J.
Adobe Systems Incorporated
Fish & Richardson P.C.
Jankus Almis R.
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