Image analysis – Image enhancement or restoration – Edge or contour enhancement
Reexamination Certificate
1998-10-06
2001-01-16
Rogers, Scott (Department: 2724)
Image analysis
Image enhancement or restoration
Edge or contour enhancement
C382S298000, C382S300000
Reexamination Certificate
active
06175659
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to image scaling, more particularly to a method and apparatus for image scaling using adaptive edge enhancement.
2. Description of the Related Art
As technology improves, integration of computer and consumer electronics has become a primary consideration to provide better functionality to consumers. When displaying a computer video graphics adapter (VGA) signal on a television screen, video signals are scaled to match the aspect ratio of digital television terminals. Image scaling in digital television terminals can provide different viewing flexibility for viewers.
Presently, image scaling uses linear interpolation or digital differential analyzer (DDA) to scale images. However, for different scaling factors, traditional approaches require a large hardware cost to meet real time video applications. In addition, image scaling often blurs the edges of differently colored portions in an image since interpolation acts as a low-pass filter when scaling images. Thus, edge enhancement has to be performed to make the scaled images sharper and clearer.
Conventional edge enhancement techniques do not produce good image quality since they do not consider image contents for subsequent image scaling. Since visual sensitivity of the human eye depends on the brightness of the background, adaptive edge enhancement can avoid the defects of conventional methods and can provide viewers with better image quality.
SUMMARY OF THE INVENTION
Therefore, the main object of the present invention is to provide a method and apparatus for image scaling using adaptive edge enhancement so as to overcome the aforementioned drawbacks that are commonly associated with the prior art.
According to one aspect of the present invention, a method for image scaling using adaptive edge enhancement comprises the steps of:
providing a plurality of sets of gradient threshold values and enhancement threshold values that correspond respectively to predetermined enhancement modes;
computing a mean pixel value for a one-dimensional pixel array that includes a center pixel to be updated and neighboring pixels of the center pixel;
selecting one of the enhancement modes based on the mean pixel value;
selecting one of the sets of gradient threshold values and enhancement threshold values based on the selected one of the enhancement modes;
computing a sharpness value by adding together absolute values of differences between values of the center pixel and each of the neighboring pixels;
selecting one of the enhancement threshold values in the selected one of the sets by comparing the sharpness value with the gradient threshold values in the selected one of the sets;
determining a sign of the selected one of the enhancement threshold values such that difference between left side brightness and right side brightness is increased when the selected one of the enhancement threshold values is added to the value of the center pixel; and
updating the center pixel by adding the selected one of the enhancement threshold values to the value of the center pixel while taking into account the sign of the selected one of the enhancement threshold values, thereby resulting in an edge-enhanced image.
Preferably, the method further comprises the steps of:
accumulating a binary accumulation factor in a binary accumulator, the accumulation factor being a quotient of an image resolution-dependent base value and a user-defined scaling factor, the accumulator having an output that includes a binary weighting output and a carry bit;
storing the pixels of the edge-enhanced image in a line buffer;
controlling the line buffer to output two consecutive pixels i and i+1 when the carry bit is 0, indicating that the weighting output is less than the base value, and to output two consecutive pixels i+1 and i+2 when the carry bit is 1, indicating that the weighting output is greater than the base value; and
interpolating the consecutive pixels from the line buffer to obtain a scaled pixel by
multiplying value of a first one of the consecutive pixels with value of first three most significant bits of the weighting output to result in a first product,
multiplying value of a second one of the consecutive pixels with difference of 8 and the value of the first three most significant bits of the weighting output to result in a second product,
adding together the first and second products to obtain a sum, and
dividing the sum by 8.
According to another aspect of the present invention, an apparatus for image scaling comprises an adaptive edge enhancement device that includes:
a threshold multiplexer having data inputs which respectively receive a plurality of sets of gradient threshold values and enhancement threshold values that correspond respectively to predetermined enhancement modes;
a mean value computing unit adapted to compute a mean pixel value for a one-dimensional pixel array that includes a center pixel to be updated and neighboring pixels of the center pixel;
an adaptive mode selector, connected to the mean value computing unit, for selecting one of the enhancement modes based on the mean pixel value;
means, interconnecting the adaptive mode selector and the threshold multiplexer, for controlling the threshold multiplexer to select one of the sets of gradient threshold values and enhancement threshold values based on the selected one of the enhancement modes;
a gradient logic computing unit adapted to compute a sharpness value by adding together absolute values of differences between values of the center pixel and each of the neighboring pixels;
a gradient level selector, connected to the threshold multiplexer and the gradient logic computing unit, for selecting one of the enhancement threshold values in the selected one of the sets by comparing the sharpness value with the gradient threshold values in the selected one of the sets;
a threshold sign selector adapted to determine a sign of the selected one of the enhancement threshold values such that difference between left side brightness and right side brightness is increased when the selected one of the enhancement threshold values is added to the value of the center pixel; and
a pixel updating unit connected to the threshold sign selector and the gradient level selector, and adapted to update the center pixel by adding the selected one of the enhancement threshold values to the value of the center pixel while taking into account the sign of the selected one of the enhancement threshold values, thereby resulting in an edge-enhanced image.
Preferably, the apparatus further comprises an image-scaling device for scaling updated pixels from the adaptive edge enhancement device. The image-scaling device includes:
a binary accumulator adapted to accumulate a binary accumulation factor therein, the accumulation factor being a quotient of an image resolution-dependent base value and a user-defined scaling factor, the accumulator having an output that includes a binary weighting output and a carry bit;
a line buffer for storing the pixels of the edge-enhanced image;
a memory access controller connected to the accumulator and the line buffer, the memory access controller controlling the line buffer to output two consecutive pixels i and i+1 when the carry bit is 0, indicating that the weighting output is less than the base value, and to output two consecutive pixels i+1 and i+2 when the carry bit is 1, indicating that the weighting output is greater than the base value; and
an interpolator, connected to the line buffer and the accumulator, for interpolating the consecutive pixels from the line buffer to obtain a scaled pixel by
multiplying value of a first one of the consecutive pixels with value of first three most significant bits of the weighting output to result in a first product,
multiplying value of a second one of the consecutive pixels with difference of 8 and the value of the first three most significant bits of the weighting output to result in a second product, adding together the first and second p
Behpour Gholam A.
Finnegan, Henderson Farabow, Garrett and Dunner L.L.P.
Rogers Scott
Silicon Intergrated Systems Corp.
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