Abstract:
An image processing apparatus, a computer readable medium and the like in which a dither effect in a neighborhood of a highlight area can be obtained easily and certainly. For this purpose, an image processing apparatus includes an inputting unit which inputs a pixel signal group representing a field image, an averaging unit ( 21 - 2  and  21 - 3 ) which performs a processing having an averaging effect among the pixel signal group input by the inputting unit, and an irregularizing unit ( 21 - 4 ) which irregularizes mutually continuous signal-values at least near a saturated level among the pixel signal group after having been processed by the averaging unit, into discontinuous signal-values.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2006-300684, filed on Nov. 6, 2006, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     The present invention relates to an image processing apparatus mounted in an electronic still camera and the like, an imaging apparatus such as an electronic still camera, and a computer readable medium. 
     2. Description of the Related Art 
     When there is an outstandingly bright object in a field to be photographed with a camera, there arises a highlight area (saturated white area) at a part of a photographed image. This highlight area has a completely flat tone differently from other area and a distinguished outline thereof provides a viewer with an unnatural impression. 
     The patent reference 1 discloses a signal processing technique to make the outline unnoticeable. This technique intentionally adds random noise to a signal at an almost saturated level. A dither effect (roughness sensation) is thereby provided to a neighborhood of the highlight area to make the outline thereof appear vague. 
     Patent reference 1: Japanese Unexamined Patent Application Publication No. 2005-72835 
     However, if this signal processing technique is applied to an electronic still camera without any modification, it is found that the dither effect can not always be obtained depending on an application method and a use condition thereof. 
     SUMMARY 
     Accordingly, an object of the present invention is to provide an image processing apparatus and a computer readable medium in which a dither effect around a highlight area can be obtained easily and certainly, and to provide an imaging apparatus which is excellent in highlight expression. 
     An image processing apparatus according to the present invention includes an inputting unit which inputs a pixel signal group representing a field image, an averaging unit which provides processing having an averaging effect in the pixel signal group input by the inputting unit, and an irregularizing unit which irregularizes mutually continuous signal-values at least near a saturated level among the pixel signal group after having been processed by the averaging unit, into discontinuous signal-values. 
     Here, the image processing apparatus according to the present invention may further includes an information-compressioning unit which performs processing having an information-compressional effect in a brightness direction on the pixel signal group after having been processed by the irregularziing unit. 
     Also, processing by the irregularizing unit is preferably tone conversional processing using a look-up table. 
     Also, contents of the look-up table are preferably set so that processing of the irregularization and other processing of tone correction can be performed on the pixel signal group at the same time. 
     Also, contents of the look-up table are preferably set so that amplitude of the irregularization can depend on a magnitude of the signal-value before the irregularization. 
     Also, the irregularizing unit preferably has multiple sorts of look-up tables with different amplitudes of the irregularization and uses these look-up tables by switching according to the number of pixel signals at a saturated level among the pixel signal group. 
     Also, the irregularizing unit preferably has multiple sorts of look-up tables with different amplitudes of the irregularization and uses these look-up tables by switching according to contents of one or more kinds of processing which are to be performed on the pixel signal group by units except for the irregularizing unit. 
     Also, an imaging apparatus according to the present invention includes an imaging sensor which captures a pixel signal group representing a field image and any of the image processing apparatus according to the present invention. 
     Also, a computer readable medium including image processing program according to the present invention, executable by an image processing apparatus, includes an inputting operation which inputs a pixel signal group representing a field image, an averaging operation which performs processing having an averaging effect among the pixel signal group input by the inputting operation, and an irregularizing operation which irregularizes mutually continuous signal-values at least near a saturated level among the pixel signal group after having been processed by the averaging unit, into discontinuous signal-values. 
     Note that the computer readable medium according to the present invention may further include an information-compressioning operation which performs processing having an information-compressional effect in a brightness direction on the pixel signal group after having been processed by the irregularizing operation. 
     Also, the processing by the irregularizing operation is preferably tone conversional processing using a look-up table. 
     Accordingly, the present invention realizes an image processing apparatus and a computer readable medium in which a dither effect around a highlight area can be obtained easily and certainly. Also, the present invention realizes an imaging apparatus which is excellent in highlight expression. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a functional block diagram of a present system; 
         FIG. 2  is a functional block diagram of an image processing part  21 ; 
         FIG. 3  is an explanatory diagram of correcting tables T L , T M , and T H ; 
         FIG. 4  is an explanatory diagram of irregularizing tables T NL , T NM , and T NH ; 
         FIG. 5  is an explanatory diagram of characteristics of the irregularizing table T NH ; 
         FIG. 6  is a diagram showing an example of a tone-converting table; 
         FIG. 7  is an operational flow chart of a CPU  24  in a shooting mode according to a first embodiment; 
         FIG. 8  is an operational flow chart of a CPU  24  regarding setting of a tone-converting table in a setting mode according to a second embodiment; and 
         FIG. 9  is a table showing relationships between various variable parameters and irregularization degrees. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     First Embodiment 
     Hereinbelow, a first embodiment according to the present invention will be described. 
     The present embodiment is an embodiment for an electronic still camera system. 
     First, a configuration of a present system will be described. 
       FIG. 1  is a functional block diagram of the present system. As shown in  FIG. 1 , the present system includes an electronic still camera body  100  and a shooting lens  200  attached to the electronic still camera body  100 . 
     The electronic still camera body  100  is attached with a portable storage medium  300  such as a card memory and includes an operating button  11 , a quick-return mirror  12 , a shutter  13 , a color imaging sensor (CCD, CMOS, etc.)  14 , an amplifier  15 , an A/D converter  16 , a signal processing circuit  17 , a frame memory  18 , an image processing part  21 , a compressionnal/decompressional processing part  22 , a storaging part  23 , a CPU  24 , a ROM  24 A, a RAM  24 B, a photometric sensor  27 , etc. The ROM  24 A preliminarily stores an operating program of the CPU  24  and various kinds of information, and the RAM  24 B temporally stores information required by the CPU  24  during operation thereof. 
     The frame memory  18 , the image processing part  21 , the compressional/decompressional processing part  22 , the storaging part  23 , the CPU  24 , the ROM  24 A and the RAM  24 B are coupled one another via a bus. When a user manipulates the operating button  11  to input various indications to the present system, the CPU  24  recognizes contents of the indications, and sets and controls each part following them to operate the present system. 
     The user can switch a mode of the present system among various modes such as a shooting mode and a setting mode by manipulating the operating button  11 . Also the user can input a release indication (shooting indication) into the present system by manipulating the operating button  11 , when the present system is in the shooting mode. Also, the user can specify which tone correction degree, “high”, “medium”, or “low”, is to be set to the present system by manipulating the operating button  11 , when the present system is in the setting mode. 
     Next, a basic operation of the present system in the shooting mode will be described. 
     When a user inputs a release indication, the CPU  24  starts to drive the quick-return mirror  12 , the shutter  13 , the color imaging sensor  14 , the amplifier  15 , the A/D converter  16 , and the signal processing circuit  17 . A pixel signal read out from the color imaging sensor  14  at this time is stored into the frame memory  18  sequentially via the amplifier  15 , the A/D converter  16  and the signal processing circuit  17 . When one frame of the pixel signals is stored in the frame memory  18 , one cycle of shooting is completed. Hereinafter, whole pixel signals of one frame are called an “image” and each pixel signal is called a “pixel”. 
     After shooting, the CPU  24  instructs the image processing part  21  to perform various kinds of image processing on an image stored in the frame memory  18 . Then, the CPU  24  instructs the compressional/decompressional processing part  22  to perform compressional processing on the image after the image processing. This compressional processing also includes information-compressional processing to reduce the number of tones of an image. For example, while the number of tones before the compressional processing is 12 bits, the number of tones after the compressional processing becomes 8 bits. Further, the CPU  24  instructs the storaging part  23  to write the image after the compressional processing into the storage medium  300 . Thereby, storing of an image is completed. 
     Next, image processing by the image processing part  21  will be described in detail. 
       FIG. 2  is a functional block diagram of the image processing part  21 . In  FIG. 2 , arrangement of each block shows an order of execution of processing by each of the blocks, and the left side is an upstream side and the right side is a down stream side. 
     As shown in  FIG. 2 , the image processing part  21  includes a white-balance processing part  21 - 1  which adjusts an intensity balance among color components of an image (R, G, and B), a pixel-interpolation processing part  21 - 2  which interpolates lacking pixels of each color component using surrounding pixels in an image, a noise reducing part  21 - 3  which makes a luminance level of an outstanding pixel in an image close to a luminance level of a surrounding pixel, a tone conversional processing part  21 - 4  which converts a luminance level of each pixel in an image using a tone-converting table, a color-conversional processing part  21 - 5  which converts a color of each pixel in an image using a color-converting matrix, a color-coordinate transforming part  21 - 6  which performs coordinate transformation from a calorimetric system (R, G, and B) of an image to other colorimetric system (Y, Cb, and Cr), an edge-reinforcement processing part  21 - 7  which reinforces an edge of a picture in an image using an edge filter, etc. 
     Among these parts, the tone conversional processing part  21 - 4  uses a tone-converting table commonly for tone conversion of an R component, tone conversion of a G component and tone conversion of a B component in an image. This tone converting table is a look-up table which is generated and set by the CPU  24 . This tone-converting table has two functions; one is a tone-correcting function which changes tone reproducibility of an image (including a gamma correction) and the other is an irregularizing function which provides a dither effect to a neighborhood of a highlight area in an image. Operation of the CPU  24  regarding generation and setting of the tone converting table will be described in detail hereinafter. 
     In the above described image processing part  21 , an execution order is not limited to the order of the white-balance processing part  21 - 1 , the pixel-interpolation processing part  21 - 2 , the noise reducing part  21 - 3 , the tone conversional processing part  21 - 4 , the color conversional processing part  21 - 5 , the color-coordinate transforming part  21 - 6 , and the edge-reinforcement processing part  21 - 7 . 
     Note that, since processing in the pixel-interpolation processing part  21 - 2  and processing in the noise reducing part  21 - 3  have an effect to average an image in a spatial direction (low-pass effect), and a noise-adding function in the tone-conversional processing part  21 - 4  and processing in the edge-reinforcement processing part  21 - 7  have an inverse effect (high-pass effect), a block with the high-pass effect (tone-conversional processing part  21 - 4  and the edge-reinforcement processing part  21 - 7 ) should be arranged in a subsequent stage of a block with the low-pass effect (pixel-interpolation processing part  21 - 2  and the noise reducing part  21 - 7 ) to obtain the maximum effects from the both blocks. 
     Next, information stored preliminarily in the ROM  24 A will be described. 
     The ROM  24 A stores preliminarily multiple sorts of correcting tables T L , T M , and T H  as shown in  FIG. 3 , and multiple sorts of irregularizing tables T NL , T NM , and T NH  as shown in  FIG. 4  as basic information for the CPU  24  to generate a tone-converting table. As shown in  FIG. 3 , differences among the correcting tables T L , T M , and T H  lie in tone correction degrees like “low”, “medium”, and “high”. As shown in  FIG. 4 , differences among the irregularizing tables T NL , T NM , and T NH  lie in irregularization degrees like “high”, “medium”, and “low”. Here, in  FIG. 4 , an increment of an input level is shown to be larger than in an actual case for easy understanding. 
     Next, characteristics of the irregularizing table T NH  will be described in detail. 
       FIG. 5  is a diagram illustrating characteristics of the irregularizing table T NH . Also in  FIG. 5 , an increment of an input level is shown to be larger than in an actual case. As shown in  FIG. 5 , the characteristics of the irregularizing table T NH  are set so as to provide a variation in a luminance level for a pixel with a luminance level belonging to a range A near a saturated level among input pixels. Converting a continuous luminance level to a discontinuous luminance level in this manner is called “irregularization” in the present specification. 
     A level change amount in this irregularization varies according to an input level, and is preliminarily determined to be a random value ranging from −α to +α. This “α” is an irregularizing amplitude. The irregularizing amplitude α is set to be larger for a higher input level. For example, as shown in  FIG. 5 , the amplitude α is set to be a small value α 2  in a lower level side range A 2  within a range A, the amplitude α is set to be a medium value α 1  in a medium range A 1  within the range A, and the amplitude α is set to be a large value α 0  in a higher level side range A 0  within the range A. 
     The above described characteristics of the irregularizing table T NH  apply similarly to the other two irregularizing tables T NL  and T NM . Note that the amplitude α is set to be a different value among the three irregularizing tables T NL , T NM , and T NH  as shown in  FIG. 4 . An amplitude α in the irregularizing table T NH  is the largest, an amplitude α in the irregularizing table T NM  is the second largest, and an amplitude α in the irregularizing table T NL  is the smallest. 
     According to the above described basic information, the CPU  24  can generate a tone-converting table such as shown in  FIG. 6 , for example, by selecting any of the correcting tables T L , T M , and T H  shown in  FIG. 3  and any of the irregularizing tables T NL , T NM , and T NH  shown in  FIG. 4  and by additively synthesizing selected two tables. The generated tone-converting table is provided with both of the tone-correcting function and the irregularization function. 
     Here, the tone-correction degree varies depending on which correcting table is used among the three correcting tables T L , T M , and T H  shown in  FIG. 3 . Also, the irregularization degree varies depending on which irregularizing table is used among the three irregularizing tables shown T NL , T NM , and T NH  shown in  FIG. 4 . 
     Next, an operational flow of the CPU  24  in the shooting mode will be described in detail. 
       FIG. 7  is an operational flow chart of the CPU  24  in the shooting mode. As shown in  FIG. 7 , when a user inputs a release indication (Step S 11  YES), the CPU  24  drives each part to carry out a shooting (Step S 12 ). The diving method of each part is as described hereinabove. 
     Then, the CPU  24  calculates a saturation ratio from an image captured in this shooting (Step  13 ). The calculation of the saturation ratio is performed, for example, as follows. The CPU  24  divides an image into multiple small areas and obtains a luminance level of each small area. The luminance level of a small area is an average luminance level of pixels within the small area. Further, the CPU  24  compares a luminance level of each small area with a threshold value and assumes a small area, where the luminance level is over the threshold value, as a highlight area. Further, the CPU  24  divides the number of the small areas assumed to be highlight areas by the number of total small areas to calculate an occupation ratio of the highlight areas on an image. This ratio is the image saturation ratio and takes any value between 0% and 100%. A lower saturation ratio has less need of irregularization and a higher saturation ratio has greater need of irregularization. 
     On the other hand, the CPU  24  determines whether a tone-correction degree indicated by the user is “high” or not (Step  14 ), and selects the correcting table T H  with a high correction degree among the correcting tables T L , T M , and T H  shown in  FIG. 3 , in the case of “high” (Step S 14  YES). 
     Also, the CPU  24  determines whether the tone-correction degree indicated by the user is “medium” or not (Step S 15 ), in the case the degree indicated by the user is not “high” (Step S 14  NO), and selects the correcting table T M  with a medium correction degree among the correcting tables T L , T M , and T H  shown in  FIG. 3  in the case of “medium” (Step  15  YES). 
     Also, the CPU  24  selects the correcting table T L  with a low correction degree among the correcting tables T L , T M , and T H  shown in  FIG. 3  in the case the degree indicated by the user is not “medium” (Step S 15  NO). 
     Further, the CPU  24  determines whether the saturation ratio calculated in Step S 13  is 5% or higher (Step S 19 ), and, in the case of 5% or higher (Step S 19  YES), the CPU  24  selects the irregularizing table T NH  with a high irregularization degree among the irregularizing tables T NL , T NM , and T NH  shown in  FIG. 4  (Step S 113 ), because need of irregularization is extremely high. 
     Also, the CPU  24  determines whether the saturation ratio is 3% or higher (Step S 111 ) in the case of lower than 5% saturation ratio (Step S 19  NO), and, in the case of 3% or higher Step S 111  YES), the CPU  24  selects the irregularizing table T NM  with a medium irregularization degree among the irregularizing tables T NL , T NM , and T NH  shown in  FIG. 4  (Step S 114 ), because need of irregularization is comparatively high. 
     Also, the CPU  24  determines whether the saturation ratio is 1% or higher (Step S 112 ) in the case of lower than 3% saturation ratio (Step S 111  NO), and, in the case of 1% or higher (Step S  112  YES), the CPU  24  selects the irregularizing table with T NL  a low irregularization degree among the irregularizing tables T NL , T NM , and T NH  shown in  FIG. 4  (Step S 115 ), because need of irregularization is low. 
     Also, the CPU  24  does not select an irregularizing table (Step S 116 ) in the case the saturation ratio is lower than 1% (Step S 112  NO), because irregularization is not needed. 
     Then, the CPU  24  synthesizes a selected correcting table and a selected irregularizing table to generate a tone-converting table. Here, when an output level after the synthesis exceeds a saturated level, the output level is clipped at the saturated level. Also, when an irregularizing table is not selected, a selected correcting table itself becomes a tone-converting table without any synthesis (Step S 117 ). 
     Further, the CPU  24  sets the generated tone-converting table to the tone-conversional processing part  21 - 4  (Step S 118 ), and starts to drive the image processing part  21 , the compressional/decompressional processing part  22 , and the storaging part  23  (Step S 119 ). The driving method of each part is as described hereinabove. 
     Next, advantages of the present system will be described. 
     The CPU  24  in the present system reflects contents of an irregularizing table (refer to  FIG. 4 ) into a tone-converting table used by the tone conversional processing part  21 - 4  (refer to  FIG. 2 ). Therefore, a dither effect can be applied to a neighborhood of a highlight area of an image without complicating a circuit within the electronic still camera  100 . 
     Also, the dither effect applied to an image can be preserved securely because the tone conversional processing part  21 - 4  (refer to  FIG. 2 ) is arranged in a subsequent stage of the pixel-interpolation processing part  21 - 2  and the noise-reducing part  21 - 3 , which have a low-pass effect. 
     Here, since the present system uses a tone-converting table for applying a dither effect, pixels with the same luminance level are converted to pixels with the same luminance level. Also, generally in a field image, pixels spatially neighboring each other have a tendency to have neighboring levels also in luminance. Therefore, there is a possibility in the present system that noise with the same value might be generated densely on an image after tone conversion. 
     In the present system, however, since the tone conversional processing part  21 - 4  is arranged in a previous stage of the compressional/decompressional processing part  22 , that is, in the previous stage of reducing processing of the number of tones, it is probable that even pixels spatially neighboring each other would have different luminance levels in an image just before the tone conversion. Therefore, in the present system, the problem that the noise with the same value might be generated densely on an image does not occur frequently. 
     Also, in the present system, image processing can be carried out efficiently, since the tone conversional processing part  21 - 4  is provided with both of the irregularizing function and the tone correcting function. 
     Also, in the present system, contents of an irregularizing table are set so that an irregularization degree depends on a luminance level of a pixel. Specifically, an irregularizing amplitude α is set to be larger for a higher luminance level (refer to  FIG. 4 ), and a boundary between an area with a dither effect and an area without a dither effect on an image can be made vague to provide a natural impression to a viewer. 
     Also, in the present system, an irregularization degree can be always set to a necessary and also a sufficient level, since which irregularizing table is used among T NL , T NM , and T NH  depends on a saturation rate of an image (Steps S 19 , S 111 , S 112 , S 113 , S 114 , and S  115  in  FIG. 7 ). 
     Also, in the present system, freedom to change tone-conversional characteristics can be made greater while suppressing a capacity of the ROM  24 A, since the correcting tables T L , T M , and T H  and the irregularizing tables T NL , T NM , and T NH  are prepared separately and combined together to generate various sorts of tone-converting tables. 
     Note that, although the number of steps for changing the tone correction degree is three and the number of steps for changing the irregularization degree is four in the present system, the number of steps for changing either of the degrees can be changed. For example, if the tone correction degree is set to be “high”, “medium”, “low”, or “zero” in the present system, the freedom to change the tone-conversional characteristics is increased to 16 degrees. 
     Also, while an object of the irregularization (here, an object of the tone conversional processing) is a newest image captured by shooting in the present system, the object may be an old image stored in the storage medium  300 . 
     Also, the CPU  24  in the present system calculates the image saturation rate directly from an image, but also may estimate the rate from a BV value indicated by an output signal of the photometric sensor  27  (refer to  FIG. 1 ). In the estimation, shooting conditions (exposure-compensating value and the like) set in the present system are preferably taken into consideration. 
     Second Embodiment 
     Hereinbelow, a second embodiment according to the present invention will be described. The present embodiment is also an embodiment for an electronic camera system. Here, only differences from the first embodiment will be described. 
     A user of a present system can specify a shooting sensitivity (ISO sensitivity) such as “1,600”, “800”, “400”, “200”, or “100” to the present system in a setting mode. A CPU  24  in the present system recognizes an ISO sensitivity specified by the user, and set a gain of an amplifier  15  accordingly (a higher gain is set for a larger specified value). 
     Also, the CPU  24  in the present system carries out generation and setting of a tone-converting table according to specifications for the ISO sensitivity and the tone correction degree in the setting mode. That is, in the present system, the generation and setting of the tone-converting table is carried out in a setting mode, not in a shooting mode. 
       FIG. 8  is an operational flow chart of the CPU  24  regarding generation and setting of a tone-converting table in the setting mode. The same step as in  FIG. 7  in  FIG. 8  is designated by the same symbol. 
     As shown in  FIG. 8 , when a user specifies an ISO sensitivity and a tone correction degree (Step S 20  YES), the CPU  24  selects any of correcting tables T L , T M , and T H  according to the tone correction degree specified by the user (Steps S 14 , S 15 , S 16 , S 17  and S 18 ). 
     Further, the CPU  24  discriminates whether the ISO sensitivity specified by the user is 200 or below (Step S 29 ), and, in the case of 200 or below (Step S 29  YES), the CPU  24  selects the irregularizing table T NH  which is a high irregularization degree, among the irregularizing tables T NL , T NM , and T NH  shown in  FIG. 4  (Step S 113 ). 
     Also, in the case that the ISO sensitivity is above 200 (Step S 29  NO), the CPU  24  discriminates whether the ISO sensitivity is 400 or below (Step S 211 ), and in the case that the ISO sensitivity is 400 or below (Step  211  YES), the CPU  24  selects the irregularizing table T NM  which is a medium irregularization degree, among irregularizing tables T NL , T NM , and T NH  shown in  FIG. 4  (Step S 114 ). 
     Also, in the case the ISO sensitivity is above 400 (Step S 211  NO), the CPU  24  discriminates whether the ISO sensitivity is 800 or below (Step  212 ), and in the case that the ISO sensitivity is 800 or below (Step  212  YES), the CPU  24  selects the irregularizing table T NL  which is a low irregularization degree, among the irregularizing tables T NL , T NM , and T NH  shown in  FIG. 4  (Step  115 ). 
     Also, in the case the ISO sensitivity is higher than 800 (Step S 212  NO), the CPU  24  does not select an irregularizing table (Step S 116 ). 
     Then, the CPU  24  synthesizes the selected correcting table and irregularizing table to generate a tone-converting table (Step S 117 ), which is set into a tone conversional processing part  21 - 4  (Step S 118 ). Details of these steps S 117  and S 118  are as described in the first embodiment. 
     As described above, the irregularization degree is set to be lower for a higher ISO sensitivity in the present system (Steps S 116 , S 115 , etc.). Since the gain of the amplifier  15  is set to be larger for a higher ISO sensitivity as described hereinabove, an S/N ratio of an image is deteriorated and an outline in a highlight area of the image tends not to be particularly unnoticeable. Therefore, it is not a problem to set the irregularization degree to be lower. 
     On the other hand, in the present system, the irregularization degree is set to be higher for a lower ISO sensitivity (Steps S 117 , S 118 , etc.). Since the gain of the amplifier  15  is set to be smaller for a lower ISO sensitivity as described above, an S/N ratio of an image is improved and an outline in a highlight area of an image tends to be noticeable. Therefore, the irregularization degree is preferably set to be higher. 
     Therefore, in the present system, the irregularization degree is always set to be appropriate according to a noise amount contained in an image. 
     (OTHERS) 
     Note that, although the irregularization degree is determined according to the image saturation rate in the first embodiment and the irregularization degree is determined according to the ISO sensitivity in the second embodiment, the irregularization degree may be determined according to other variable parameters of a system. 
     For example, in a system in which a chromatic correction degree of an image is variable, the irregularization degree may be determined according to a chromatic correction degree. In this case, the irregularization degree is preferably set to be higher for a lower chromatic correction degree. Here, change of the chromatic correction degree is carried out by change of characteristics (color-converting matrix) of the color-conversional processing part  21 - 5  (refer to  FIG. 2 ). 
     Also, in a system in which a degree of edge reinforcement of an image is variable, the irregularization degree may be determined according to a degree of edge reinforcement. In this case, the irregularization degree is preferably set to be higher for a lower degree of edge reinforcement. Here, change of the degree of edge reinforcement is carried out by change of characteristics (edge filter) of the edge-reinforcement processing part  21 - 7  (refer to  FIG. 2 ). 
     Also, although the irregularization degree is determined according to only one of variable parameters in the systems described hereinabove, the irregularization degree may be determined according to two or more variable parameters. For reference, relationships between various variable parameters and the irregularization degree are summarized in  FIG. 9 . 
     Also, although the irregularizing function is included in the tone conversional processing part  21 - 4  (refer to  FIG. 2 ) in the systems described hereinabove, the irregularizing function may be included in other block arranged in a subsequent stage of the pixel-interpolation processing part  21 - 2  and the noise reducing part  21 - 3  and in a previous stage of the compressional/decompressional processing part  22 . 
     For example, a block that performs tone conversional processing on each of chroma signals (Cb, and Cr) may be inserted between the color-coordinate transforming part  21 - 6  and the edge reinforcement processing part  21 - 7 , and contents of a tone-converting table used for the tone-conversional processing may be reflected with contents similar to those of the irregularizing table ( FIG. 4 ). 
     Also, although an image processing function, a information-compression processing function, and a controlling function are allotted to the image processing part  21 , the compressional/decompressional processing part  22 , and the CPU  24  in the systems described hereinabove, a part of or whole processing of the image processing part  21  may be carried out by the CPU  24  or a part of or whole processing of the compressional/decompressional processing part  22  may be carried out by the CPU  24 . In either case, an operating program of the CPU  24  is stored in the ROM  24 A. 
     Also, while the system described hereinabove is an electronic still camera system with an exchangeable lens, the system may be changed into other imaging apparatus such as an electronic still camera with an integrated lens, or a video camera. 
     Also, a part of or whole function regarding image processing in the systems described hereinabove can be mounted in not only imaging apparatus but also a variety of apparatuses capable of capturing an image such as an image storager, a printer, and the like. Also, a part of or whole of the image processing may be carried out by a computer. 
     The many features and advantages of the embodiments are apparent from the detailed specification and, thus, it is intended by the appended claims to cover all such features and advantages of the embodiments that fall within the true spirit and scope thereof. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the inventive embodiments to the exact construction and operation illustrated and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope thereof.