Patent Application
20070292041
Hereinafter, embodiments of the invention will be described with reference to the drawings.
The MFP M according to this embodiment comprises the image processing apparatus 1 and an image forming unit 2. The image processing apparatus 1 plays a role of applying specific filtering processing on an image signal of an image subject to processing. Also, the image forming unit 2 plays a role of performing image forming processing on a sheet according to a processing result in the image processing apparatus 1. As the image signal of an image subject to processing referred to herein, data obtained by applying several kinds of specific processing on image data (so-called raw data) outputted directly from a CCD or the like will be described by way of example; however, raw data itself may be used as an image signal of the image subject to processing.
Hereinafter, the configuration of the image processing apparatus 1 according to this embodiment will be described in detail. The image processing apparatus 1 according to this embodiment comprises a discrimination information generation unit 101, a low-pass filter (first filter processing unit) 102, a band-pass filter (second filter processing unit) 103, a conversion information selection unit 104, an enhancement quantity conversion unit 105, a signal synthesis unit 106, a CPU 801, and a memory 802.
The discrimination information generation unit 101 generates a DSC signal (discrimination information) to discriminate kinds of image formed of respective pixels from one another by performing at least any one of “edge detection processing”, “achromatic color judgment processing”, and “halftone dot judgment processing” on image signals of pixels forming an image subject to processing. The DSC signal generated in the discrimination information generation unit 101 is the information to discriminate pixels forming an image (equivalent to an image of individual characters and photographs contained in an image subject to processing) of at least any one of “black character”, “color character”, and “photograph” from the others. For an image signal identified as forming a character, the discrimination information generation unit 101 compares the values of image signals of respective colors including RGB or CMY, and judges the image signal as forming a black character when a difference among the signal values is within the pre-set threshold value, after which it classifies the DSC signal into “black character” and “color characters”. The DSC signal generated in the discrimination information generation unit 101 is transmitted to the low-pass filter 102, the band-pass filter 103, and the conversion information selection unit 104 that will be described below.
The low-pass filter (first filter processing unit) 102 applies smoothing processing on image signals of respective pixels forming an image subject to processing. Of the RGB or CMY image signals, DC (direct current) smoothed by the filter processing in the low-pass filter 102 alone is extracted and outputted.
The band-pass filter (second filter processing unit) 103 is also referred to as a high-pass filter and applies processing to enhance a particular image frequency band on an image signal. To be more concrete, the second filter processing unit 103 applies enhancement processing to enhance image signals of pixels forming characters in an image subject to processing in comparison with image signals of pixels forming an edge portion of a patch region having uniform density, such as a filled-in figure. For an image signal IMG inputted into the band-pass filter 103, it is set in such a manner that a total of filter coefficients will be 0, and an enhancement component, Δx, alone is extracted.
The low-pass filter 102 and the band-bass filter 103 acquire the DSC signal generated in the discrimination information generation unit 101, and perform specific filter processing by changing the parameter of the filter coefficient according to this DSC signal.
The conversion information selection unit 104 acquires the DSC signal generated in the discrimination information generation unit 101. According to the acquired “DSC signal”, the conversion information selection unit 104 selects an LUT (Look-Up Table) corresponding to this DSC signal among plural LUT's (specific conversion information) to convert quantities of enhancement for image signals of respective pixels on which the enhancement processing has been applied in the second filter processing unit 103. Herein, three kinds of LUT's for uses of “photograph”, “color character”, and “black characters” have been previously prepared and stored, for example, in the memory 802.
The enhancement quantity conversion unit 105 converts a quantity of enhancement of an image signal on which the enhancement processing has been applied in the second filter processing unit 103 according to the LUT selected in the conversion information selection unit 104. To be more concrete, for example, of the image signals on which the enhancement processing has been applied in the second filter processing unit 103, the enhancement quantity conversion unit 105 reduces a quantity of enhancement of image signals of pixels forming the edge portion of the patch region according to the LUT selected in the conversion information selection unit 104.
The signal synthesis unit 106 adds and thereby synthesizes, pixel by pixel, an image signal on which the smoothing processing has been applied in the first filter processing unit 102 and an image signal whose quantity of enhancement has been converted in the enhancement quantity conversion unit 105. The image signal synthesized in the signal synthesis unit 106 undergoes specific processing, such as clipping processing, and is then transmitted to the image forming unit 2 described below.
The CPU 801 plays a role of performing various kinds of processing in the image processing apparatus 1 and in the MFP M, and also plays a role of exerting various functions by executing a program stored in the memory 802. The memory 802 comprises, for example, a ROM or a RAM, and plays a role of storing various kinds of information and programs used in the image processing apparatus 1.
The image forming unit 2 forms an image on a sheet according to an image signal for which the filtering processing in the image processing apparatus 1 has been completed (synthesized in the signal synthesis unit 106) as described above.
The image processing apparatus 1 according to this embodiment is able to convert the degree of enhancement non-linearly in response to an image signal level (quantity of enhancement) after the filter processing in the band-pass filter 103 with the use of the LUT. It is thus possible to adjust the degree of enhancement by discriminating between “pixels forming the edge portion of the patch regions” and “pixels forming characters” when there is a difference in quantity of enhancement. Also, by including a signal to discriminate “black character” from the other in the DSC signal used as the reference when an LUT is selected in the conversion information selection unit 104, it is possible to discriminate pixels forming a black character from pixels forming a color character, which in turn enables the enhancement quantity conversion unit 105 to convert a quantity of enhancement for a black character independently.
The quantity of enhancement, Δx, outputted as the result of the filter processing in the band-pass filter 103 varies with the kind of image in the document formed of a pixel subjected to the filter processing. For example, for a pixel forming a character or a line, a quantity of enhancement is large, whereas a quantity of enhancement for a pixel forming the edge portion of the patch region is not as large as that for a character (see
The enhancement quantity conversion unit 105 exploits this characteristic, and leaves a quantity of enhancement intact for image signals of pixels forming a character portion for which the sharpness effect is needed, and reduces a quantity of enhancement for image signals of pixels forming the edge portion of the patch region for which enhancement needs to be suppressed, using, for example, the LUT as shown in
Generally, a primary importance is placed on reproduction (enhancement) of “black character” when the filter processing is performed. Hence, in this embodiment, the degree of enhancement quantity conversion is differentiated between “color character” and “black character” (see
The discrimination information generation unit 101 generates discrimination information used to discriminate kinds of image formed of the respective pixels from one another by performing at least any one of the edge detection processing, the achromatic color judgment processing, and the halftone dot judgment processing on image signals of pixels forming an image subject to processing (discrimination information generating step) (S101).
The discrimination information is information to discriminate pixels forming an image of at least any one of a black character, a color character, and a photograph from the others.
The first filter processing unit 102 applies the smoothing processing on image signals of respective pixels forming the image subject to processing (first filter processing step) (S102).
The second filter processing unit 103 applies processing to enhance a particular image frequency band on the image signals (second filter processing step) (S103).
The conversion information selection unit 104 acquires the discrimination information to discriminate kinds of image formed of the respective pixels forming the image subject to processing from one another. According to the acquired discrimination information, the conversion information selection unit 104 then selects conversion information corresponding to this discrimination information among plural kinds of specific conversion information to convert quantities of enhancement of image signals of respective pixels on which the enhancement processing has been applied in the second filter processing step (conversion information selecting step) (S104).
According to the conversion information selected in the conversion information selecting step, the enhancement quantity conversion unit 105 converts quantities of enhancement of image signals on which the enhancement processing has been applied in the second filter processing step (enhancement quantity converting step) (S105).
The signal synthesis unit 106 synthesizes, pixel by pixel, the image signals on which the smoothing processing has been applied in the first filter processing step and the image signals whose quantities of enhancement have been converted in the enhancement quantity converting step (signal synthesizing step) (S106).
The second filter processing unit 103 applies the enhancement processing to enhance image signals of pixels forming characters in the image subject to processing in comparison with image signals of pixels forming the edge portion of the patch region (second filter processing step). Of the image signals on which the enhancement processing has been applied in the second filter processing step, the enhancement quantity conversion unit 105 reduces a quantity of enhancement for image signals of pixels forming the edge portion of the patch region according to the conversion information selected in the conversion information selecting step (enhancement quantity converting step).
The flowchart described above shows a case where the discrimination information generating step is performed first followed sequentially by the first filter processing step and the second filter processing step. However, the order is not limited to this case, and the order is not particularly limited as long as the first filter processing step is performed before the execution of the signal synthesizing step and the second filter processing step is performed before the enhancement quantity converting step.
Each step of the processing in the image processing apparatus described above is exerted by causing the CPU 801 to execute the image processing program stored in the memory 802 on the basis of image processing information stored in the memory 802 and outside input information, such as control panel settings and printer driver settings, and by setting the results in the image processing apparatus.
This embodiment has described a case where functions needed to practice the invention have been previously recorded inside the apparatus. The invention, however, is not limited to this case, and the same functions may be down loaded to the apparatus via a network, or a recording medium having stored the same functions may be installed in the apparatus. The recording medium can be of any type, such as a CD-ROM, as long as it is a recording medium capable of storing the program and readable by the apparatus. Also, the functions obtained by way of pre-installment or downloading as described above may be exerted in cooperation with the OS (Operating System) or the like inside the apparatus.
As has been described, according to this embodiment, by providing an LPF (Low-Pass Filter) that performs the smoothing processing and a BPF (Band-Pass Filter) that performs the enhancement processing separately, and by further providing the enhancement quantity conversion processing using an LUT (Look-Up Table) in response to the DSC signal at the stage after the BPF, it is possible to convert the degree of enhancement non-linearly in response to the image signal level (quantity of enhancement) after the BPF processing. A quantity of enhancement can be thus controlled in response to the characteristic of an image using a simple hardware configuration by setting an LUT such that leaves a quantity of enhancement intact (or further increases a quantity of enhancement) for characters and lines having a large quantity of enhancement and reduces a quantity of enhancement for an edge portion in the patch region where enhancement needs to be suppressed.
Further, by using a character discrimination signal to discriminate finely between black characters and color characters for an enhancement quantity conversion LUT, it is possible to achieve an effect of differentiating processing for black characters for which the sharpness effect is particularly needed from processing for color characters for which a quantity of enhancement needs to be controlled.
While the present invention has been described in detail by way of a particular embodiment, it is obvious to those skilled in the art that various modifications and alternations are possible without deviating from the spirit and the scope of the invention.
As has been described in detail, the present invention can provide an image processing technique for enabling a quantity of enhancement to be controlled in response to the characteristic of an image using a simple configuration.
