The present invention relates generally to video image processing and, more particularly, to a system and method for improving image sharpness in video display.
Previous edge enhancement methods use a max-min refinement search circuit to detect maximum and minimum turning points closest to the center of the process window and use these turning points to determine values and locations of maximum and minimum pixels of the edge. With these determined maximum and minimum pixels, the input pixel is enhanced by a predefined enhancement curve controlled by a selective edge control.
In these methods, the maximum and minimum pixels of the edge are determined by the turning points. The turning points are detected by sign of the first derivative of three neighbor pixels. However, the use of turning point detection is sensitive to noise and will create a “striped noise” artifact, which is an unexpected striped noise observable between two narrow edges, in the enhanced result.
A system is provided. The system comprises an input unit configured to receive an input signal Yin, a vertical enhancement unit configured to perform a vertical enhancement of an edge of the input signal Yin to generate an output YEV, and a horizontal enhancement unit configured to perform a horizontal enhancement of the edge of the input signal Yin to generate an output YEH. The system also comprises a local gradient analysis unit configured to generate a local gradient direction GradDir and a local gradient magnitude GradMag based at least partly upon the input signal Yin, and a mixer configured to generate an output Yout by mixing the output YEV with the output YEH using the local gradient direction GradDir. The system further comprises an output unit configured to output the output Yout.
An apparatus is provided. The apparatus comprises an edge enhancement system. The system comprises an input unit configured to receive an input signal Yin, a vertical enhancement unit configured to perform a vertical enhancement of an edge of the input signal Yin to generate an output YEV, and a horizontal enhancement unit configured to perform a horizontal enhancement of the edge of the input signal Yin to generate an output YEH. The system also comprises a local gradient analysis unit configured to generate a local gradient direction GradDir and a local gradient magnitude GradMag based at least partly upon the input signal Yin, and a mixer configured to generate an output Yout by mixing the output YEV with the output YEH using the local gradient direction GradDir. The system further comprises an output unit configured to output the output Yout.
A method is provided. The method comprises receiving an input signal Yin at an input unit, performing a vertical enhancement of an edge of the input signal Yin at a vertical enhancement unit to generate an output YEV, and performing a horizontal enhancement of the edge of the input signal Yin at a horizontal enhancement unit to generate an output YEH. The method also comprises generating a local gradient direction GradDir and a local gradient magnitude GradMag based at least partly upon the input signal Yin at a local gradient analysis unit. The method further includes generating an output Yout at a mixer by mixing the output YEV with the output YEH using the local gradient direction GradDir, and outputting the output Yout at an output unit.
For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts:
This disclosure provides a method and system for improving the quality of video images in terms of sharpness and depth perception. The improvements are carried out by steepening edge transitions using a noise robust method and system. The disclosed method and system solve problems associated with noise, jagged edges, and aliasing in high frequency region.
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The min/max search window 201 is a one-dimensional analysis window, where the pixel at the center of the process window is referred to as the current input pixel Yin. The size of the analysis window will affect the range of maximum and minimum pixel values detected and thus affects the effectiveness of the edge enhancement. The guideline for selecting a sufficient window size is whether the window is large enough to cover the edges of interest. Normally, for a rescaled standard definition (SD) or high definition (HD) input source, the window size should be larger than SD input source. For example, the window size is 9 pixels for an SD source while the window size can be 13 pixels for a rescaled SD or HD source.
The COG-based min-max search unit 202 detects the local minimum and maximum pixels within the analysis window based on the COG position of the left and right parts of the window.
The COG-based min-max search unit 202 performs a search process. As shown in
In a particular embodiment, the COG positions are estimated by units 301 and 302 as shown in Equations 1 and 2 below:
where N is the size of the min-max search window 201, y(i) is the pixel value at position i, and MeanY is the average value of the pixels in the min-max search window 201 and is calculated as shown in Equation 3 below:
Of course one of ordinary skill in the art would recognize that other methods of calculating the COG positions may be utilized without departing from the scope of this disclosure.
After calculating the COG position of the left and right parts, the minimum and maximum pixels are estimated in a maximum-minimum refinement search unit 303 of the COG-based min-max search unit 202. In a particular embodiment, the refinement search of maximum and minimum pixel values (MAX_Y, MIN_Y) and their positions (MAX_POS, MIN_POS) are defined as shown in Equations 4 to 7 below:
Of course one of ordinary skill in the art would recognize that other methods of calculating the maximum and minimum pixel values (MAX_Y, MIN_Y) and their positions (MAX_POS, MIN_POS) may be utilized without departing from the scope of this disclosure.
Using the maximum and minimum positions, an edge width information (EdgeWidth) is obtained as shown in Equation 8 below:
EdgeWidth=abs(MAX_POS−MIN_POS). [Eqn. 8]
Of course one of ordinary skill in the art would recognize that other methods of calculating the edge width information may be utilized without departing from the scope of this disclosure.
This parameter is used as a control parameter in the enhancement strength control unit 204.
The outputs of the COG-based min-max search unit 202, the maximum value (MAX_Y), the minimum value (MIN_Y) and the input Yin are then fed into the edge enhancer 203. In the edge enhancer 203, an enhancement curve is defined according to the maximum and minimum pixel values (MAX_Y, MIN_Y). This curve is controlled by a control parameter (Gain) to control the strength of the enhancement. One of ordinary skill in the art would be familiar with the concept of enhancement curves.
In this example, the minimum and maximum values are 0 and 200.
The control parameter (Gain) of the edge enhancer 203 is generated in the enhancement strength control unit 204. As shown in
FreConst=1−FreqRate. [Eqn. 9]
Of course one of ordinary skill in the art would recognize that other relationships between FreqRate and FreqConst may be realized without departing from the scope of this disclosure.
The gradient control unit 502 combines the features of gradient magnitude (GradMag), gradient direction (GradDir) and edge width (EdgeWidth) to generate a control parameter GradConst as shown in Equation 10 below:
GradConst=f(GradMag,GradDir,EdgeWidth), [Eqn. 10]
where f(.) is a combination function that can be pre-defined by users.
GradMag′=GradMag*N/EdgeWidth, [Eqn. 11]
where N is the number of pixels in the analysis window.
Of course one of ordinary skill in the art would recognize that other methods of calculating the GradMag′ may be utilized without departing from the scope of this disclosure.
From
Referring to
Gain=FreqConst*GradConst. [Eqn. 12]
Referring to
where Sign(.) is the sign function, i.e.,
⊕ is Exclusive-Or, i.e.,
Of course one of ordinary skill in the art would recognize that other methods of calculating the local frequency information may be utilized without departing from the scope of this disclosure.
The local gradient analysis unit 104 estimates the gradient magnitude and gradient direction in a 3×3 neighborhood window as shown in
GradMagX=(X1+2*X2+X3−(X6+2*X7+X8))/4, and [Eqn. 15]
GradMagY=(X1+2*X4+X6−(X3+2*X5+X8))/4. [Eqn. 16]
and the Gradient Direction (GradDir) is obtained by:
GradDir=arctan((GradMagY)/(GradMagX)), [Eqn. 17]
where arctan(y/x) is an inverse tangent function.
Of course one of ordinary skill in the art would recognize that other methods of calculating the gradient magnitude in horizontal direction (GradMagX) and vertical direction (GradMagY) may be utilized without departing from the scope of this disclosure.
The gradient magnitude in horizontal direction (GradMagX) will be used in horizontal enhancement while the gradient magnitude in vertical direction (GradMagY) will be used in vertical enhancement.
Referring to
Yout=(GradDir*YEH+(90−GradDir)*YEV)/90. [Eqn. 18]
Of course one of ordinary skill in the art would recognize that other methods of mixing horizontal enhancement (YEH) and vertical enhancement (YEV) may be utilized without departing from the scope of this disclosure.
The enhancement of edges in the vertical direction is the same as the enhancement of edges in the horizontal direction as provided in the description of
The apparatus 1000 includes a memory 1002, a processing unit 1004, an input unit 1006, and an output unit 1008 that are configured to implement the edge enhancement technique described herein. The memory 1002 may be fixed or removable and includes computer code for execution by the processing unit 1004. The processing unit 1004 includes the noise-robust edge enhancement system 100 and any suitable processing system or unit, such as a microprocessor, microcontroller, digital signal processor, application specific integrated circuit, or field programmable gate array. The input and output units 1006 and 1008 include any suitable structures for receiving or transmitting information.
In some embodiments, the input unit 1006 is configured to receive the Yin input signal. The processing unit 1004 is configured to implement the edge enhancement technique described in this disclosure. The output unit 1008 is configured to output the final enhancement output (Yout).
While the apparatus 1000 is shown using a processing unit 1004 and a memory 1002 that includes program code, other embodiments could be used. For example, the apparatus 1000 or the processing unit 1004 may be implemented with fixed or programmable logic configured to perform the methods of this disclosure.
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The local minimum and maximum pixels detection of this disclosure is based on the position of the center of gravity (COG). This is a noise-immune approach for finding minimum and maximum pixels used in edge enhancement, and solves the problem of noise sensitivity associated with previous methods.
Enhancement strength is adaptive to a combination of local features such as gradient magnitude, gradient direction and edge width. This reduces the edge jaggedness and unnatural effects in the smooth region.
Local frequency estimation and constraints reduce the aliasing in high frequency region.
Mixing of the horizontal and vertical enhancement results is adaptive to the local gradient direction. This reduces the edge jaggedness and aliasing problems, especially near the horizontal and vertical edges.
The methods and systems of this disclosure can be applied to a generic video image processing system. The methods and systems can be applied on luminance and chrominance signals separately in the YUV color space or applied in R, G, B signals separately in the RGB color space. This enhances the edge in the horizontal and the vertical directions simultaneously and then mixes the results adaptive to the gradient direction.
Although the present disclosure has been described with an exemplary embodiment, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims.