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To elucidate the significant progress in specialized areas, the editors invited renowned authorities to address specific research challenges and recent trends in their area of expertise.

Keywords/Phrases

The book begins by focusing on color fundamentals, including color management, gamut mapping, and color constancy. The remaining chapters detail the latest techniques and approaches to contemporary and traditional color image processing and analysis for a broad spectrum of sophisticated applications, including:. Color Image Processing: Methods and Applications is a versatile resource that can be used as a graduate textbook or as stand-alone reference for the design and the implementation of various image and video processing tasks for cutting-edge applications. Additional material is available at the companion web site www.

A book on Color Image Processing! Vector and semantic processing. Secure imaging. Object recognition and feature detection. Facial and retinal image analysis. Digital camera image processing. Spectral and superresolution imaging. Image and video colorization. Furthermore, according to the present invention, the foregoing object is also attained by providing a signal processing method for processing an image signal comprising: a hue difference detection step of detecting a hue difference between adjoining pixels; and a luminance edge enhancement step of enhancing an edge pixel in an image by amplifying an edge luminance signal by a gain determined on the basis of the hue difference detected at the hue difference detection step.

Further, according to the present invention, the foregoing object is also attained by providing a signal processing method for processing an image signal comprising: a hue difference detection step of detecting a hue difference between adjoining pixels; a plurality of luminance signal generation steps of generating a plurality of luminance signals by applying different processing on an input luminance signal; a selection step of selecting one of the plurality of luminance signals on the basis of the hue difference detected in the hue difference detection step; and a processing step of applying a predetermined signal process on the luminance signal selected in the selection step.

Further, according to the present invention, the foregoing object is also attained by providing a signal processing method for processing an image signal comprising: a hue difference detection step of detecting a hue difference between adjoining pixels; a plurality of luminance signal generation steps of generating a plurality of luminance signals by applying different processing on an input luminance signal; an operation step of operating the plurality of luminance signals using a value obtained on the basis of the hue difference detected in the hue difference detection steps and outputting an operation result; and a processing step of applying a predetermined signal process on the operation result outputted in the operation step.

Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.

Past Conference | Signal and Image Processing

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention and, together with the description, serve to explain the principles of the invention. A preferred embodiment of the present invention will be described in detail in accordance with the accompanying drawings.

Application of digital image processing

A signal from an image sensing element is adjusted in WB by a white balance WB circuit , delayed by a delay circuit The image sensing element is covered with filters of a Bayer layout as shown in FIG. However, the advantage of the present invention can be achieved when filters of plural colors arranged in a predetermined check pattern are used. Thereafter, a luminance signal is sent to a luminance notch circuit Further, the luminance notch circuit applies edge enhancement processing to the luminance signal using an aperture circuit.

Thereafter, a horizontal bandpass filter HBPF circuit and vertical bandpass filter VBPF circuit shift up frequency components slightly lower than the Nyquist frequency decreased by the notch filters. An adder adds the horizontal and vertical components, then the resultant signal is inputted to an aperture control APC main gain circuit Further, a color interpolation circuit interpolates chroma signals e.

A color conversion matrix MTX circuit performs color correction and converts the chroma signals to luminance Y signals and color difference Cr, Cb signals. The luminance and color difference signals thus generated are sent to the color image edge detector The color image edge detector detects color image edges of different hues.

An example of color image edge detection method performed by the color image edge detection circuit will be explained with reference to a flowchart in FIG. First in step S 1 , the hue angle of each pixel is attained. Let the hue angle to be attained be Hue, a red signal value be R, and a blue signal value be B, and a luminance value be Y, then the hue angle is obtained by the following equation.

Then, differences between hue angles of adjoining pixels in the horizontal and vertical directions may be in the oblique direction are calculated in step S 2. When the pixels near the color image edge have hue angles as shown in FIG. In step S 3 , the difference between hue angles calculated in step S 2 are diffused in the opposite directions for a predetermined number of pixels.

For instance, when diffusing the difference horizontally, the difference is diffused in the right and left directions. Similarly, when diffusing the difference vertically, the difference is diffused upward and downward. Upon performing the diffusion, if a pixel to which a difference is to be diffused already has a value, then the value whose absolute value is larger than the other is kept.

The diffusion is performed because luminance jaggedness often occurs in one or two pixels of a color image edge. Finally, in step S 4 , the difference of hue angles in the horizontal and vertical directions if differences are calculated also in the vertical direction, then those differences are also included are synthesized added for each pixel.

Color Image Processing and Applications

The hue angle difference detected value is inputted from the color image edge detector to the APC main gain circuit , and main gain of the APC main gain circuit is controlled in accordance with the hue angle difference detected value. More specifically, since the hue angle difference detected value becomes large at an edge portion, the main gain is set lower as the output from the color image edge detector is larger. Thereby preventing jaggedness of a color image edge between different hues from being enhanced in an aperture correction.

Meanwhile, the luminance signal and color difference signals are sent from the color conversion MTX circuit to the color image edge detector as well as to a chroma suppress CSUP circuit , which suppresses the color-difference gain in low and high luminance regions, and a chroma low-pass filter CLPF circuit limits the band of the chroma signals. A chroma gain knee circuit adjusts the chroma gain of the luminance and color difference signals, and a linear clip matrix LCMTX circuit finely adjusts the hue as well as corrects shift in hue due to variation in quality of image sensing elements.

According to the first embodiment as described above, a color image edge, between colors having different hues, which causes jaggedness in an image is detected and an aperture gain for a luminance signal is controlled, thereby greatly reducing a change of jaggedness at a color image edge being enhanced in aperture enhancement processing.


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As a result, a high quality luminance signal is generated. Next, the second embodiment of the present invention will be explained. The purpose of the second embodiment is the same as that of the first embodiment, which is to reduce jaggedness at a color image edge. The second embodiment introduces a configuration of adaptively switching between a low frequency component of a luminance signal Yg obtained by the out of green method a method of generating a luminance signal only from green signals often used for generating a luminance signal for video signals and a low frequency component of a luminance signal Yh obtained by the notch method.

First, the out of green method is explained. In the out of green method, a green G signal is generated by adaptive interpolation, and the G signal is used as a luminance signal. Since the luminance signal is generated from signals of a single color in the out of green method and thus the spatial frequency of the single color for sampling image signals is lower than the notch method as seen in FIG. In the out of green method, correlation between adjoining pixels of a pixel to be interpolated in the horizontal and vertical directions is determined, and if the correlation is higher in the vertical direction than in the horizontal direction, then the pixel is interpolated using values of upper and lower pixels, whereas, if the correlation is higher in the horizontal direction than in the vertical direction, then the pixel is interpolated using values of the right and left pixels.

In this manner, a proper luminance signal is generated. The out of green method will be described in more detail below. The interpolation method is changed based on the calculated absolute values. Green signals adaptively interpolated as above are used as luminance signals. It should be noted that the luminance notch circuit interpolates for R, G and B signals in the similar manner as described above, and generates luminance signals using all of the R, G and B signals. Since luminance signals are generated by adaptive interpolation using only G signals in the out of green method, by using the luminance signals generated by the out of green method in a case where an opposite hue edge are detected, jaggedness does not occur.

Further, in a normal area, i. Next, processing of luminance signals according to the second embodiment will be described with reference to FIGS. Referring to FIG.

Colour Image Processing and Applications Digital Signal Processing

The low frequency component YgLow is subtracted from the Yg signal by a subtractor , thereby the high frequency component of the luminance signal, YgHigh, is obtained. Further, for equating the ratio between color components of the luminance signal obtained by the out of green method and that of the luminance signal obtained by the notch method, a low frequency component of the luminance signal obtained by the notch method is used instead of YgLow.

For this purpose, the luminance signal Yh from the luminance notch circuit is inputted to the switch as well as to an LPF circuit , and the low frequency component of the luminance signal, YhLow, is outputted from the LPF circuit in step S Calculation method of hue angle difference detected value performed in the color image edge detector is the same as that explained in the first embodiment, therefore the explanation of the method is omitted here.

Then, when the hue angle difference detected value is less than or equal to a predetermined threshold value Th NO in step S 26 , then the luminance signal Yh is outputted from the luminance notch circuit step S An adder adds the horizontal and vertical components, then the resultant signal is inputted to an aperture control APC main gain circuit and amplified by a main gain.

Signals and Systems

Processes performed by CSUP circuit and its subsequent circuits are the same as those described in the first embodiment with reference to FIG. It should be noted that, when the luminance signal Yh generated by the luminance notch circuit is selected by the switch , the gain of the APC main gain circuit may be changed in accordance with the value of the hue angle difference detected value from the color image edge detector According to the second embodiment as described above, a luminance signal generated by the notch method is used in a normal area, and a luminance signal generated by the out of green method is used at an opposite hue edge.

Thus, jaggedness at the opposite hue edge can be reduced by utilizing the luminance signal generated by the out of green method. In addition, resolution of color image edges other than green in a normal area is not lost by using the luminance signal generated by the notch method, where the drop of the resolution is a problem of the out of green method. Further, the low frequency component of the luminance signal obtained by the out of green method is replaced by that of the luminance signal obtained by the notch method, therefore, ratios of the color components are kept the same between the luminance signals generated by the notch method and the out of green method.

A configuration for realizing the above operation is shown in FIG.


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Further in FIG. Similarly to the first and second embodiments, the color image edge detector outputs a hue angle difference detected value of a given pixel. Accordingly to the modification, in addition to the same advantages as the second embodiment, sudden change in luminance due to switching between two types of luminance signals is avoided.

According to the present invention as described above, it is possible to greatly reduce a possibility of jaggedness occurred at color image edges being enhanced by edge enhancement, thereby it is possible to generating a luminance signal of high quality.


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The present invention can be applied to a system constituted by a plurality of devices e.