Abstract:
The present invention realizes a function equivalent to an optical half-ND filter electrically and incorporates this function in an image-signal processing system, thereby to compress the dynamic range of images, both effectively and flexibly. The present invention provides an imaging apparatus including an imaging unit that photographs an object, thereby to generate a video signal, a pattern-generating unit that generates a two-dimensional gradation pattern, and a multiplying unit that multiplies the video signal by a gain that corresponds to the two-dimensional gradation pattern.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS  
       [0001]     The present invention contains subject matter related to Japanese Patent Application JP 2004-344793 filed in the Japanese Patent Office on Nov. 29, 2004, the entire contents of which being incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an imaging apparatus that has the function of compressing the dynamic range of images, and to a method of processing images.  
         [0004]     2. Description of the Related Art  
         [0005]     In most imaging apparatuses, the dynamic range of an image is compressed, thereby to reduce the difference in brightness between the parts of the image.  
         [0006]     Two methods of compressing the dynamic range are available. One method is to correct the gradation of the entire image. The other method is to correct the gradation of only the low-frequency components of the image. In the former, the gradation is corrected by means of the gamma correction, the knee correction, or the so-called histogram equalization, thereby compressing the dynamic range. In the latter, the gamma correction, the knee correction or the like is performed, thereby compressing the dynamic range.  
         [0007]     In most cases, an image whose dynamic range must be compressed is one obtained by applying two or more illumination light beams that greatly differ in intensity. A method is available, which can effectively compress the dynamic range of such an image (see Jpn. Pat. Appln. Laid-Open Publication 2001-275015). In this method, the parts of the image, other than the edges, are smoothed, while leaving the edges unprocessed. Next, a compression ratio is determined from the level of the parts smoothed. Finally, the dynamic range of the entire image is compressed in accordance with the compression ratio.  
         [0008]     In this method, the image smoothed is a control signal. The minute amplitude-components remain uncompressed. The method therefore can provide images that can be well recognized visually, because their dynamic range has been compressed.  
       SUMMARY OF THE INVENTION  
       [0009]     The method in which any highlighted part of an image is compressed by the knee correction or histogram equalization, thus performing the so-called gradation conversion, is disadvantageous in two respects. First, the image of the object is degraded in contrast, though the highlighted part compressed and any low-histogram luminance part are compressed in terms of dynamic range. Second, the gradation cannot be compressed in accordance with the two-dimensional distribution of luminance in the image, because the compression of gradation depends solely on the luminance distribution about the pixels.  
         [0010]     Any part of an image, which will be most likely highlighted when the object is photographed, is fixed in brightness and pattern, and its position scarcely changes. Examples of such an image part are the sky and a dark side of a building. There is a method of correcting the difference in brightness between the parts of such an image. In this method, an optical half-ND filter is attached to the camera, either in front of the lens or at the back thereof, and is then rotated to align the ND part with the sky part or the bright side of the building and thus adjusted in position. (The optical half-ND filter is a filter one half of which is an ND filter.) This method is, however, disadvantageous in two respects. First, it requires some knotty operations to photograph the object, i.e., the attaching of the optical half-ND filter and the rotating thereof. Second, the optical half-ND filter cannot cope with the case where the image part that will likely to be highlighted changes in brightness or pattern. This is inevitable because the filter has an inherent attenuation pattern and an inherent attenuation rate.  
         [0011]     In view of the foregoing, it is desirable to realize a function equivalent to an optical half-ND filter electrically and incorporate this function in an image-signal processing system, thereby to compress the dynamic range of images, both effectively and flexibly.  
         [0012]     The other objects of this invention and the specific advantages of the invention will be more apparent from the following description of the embodiments.  
         [0013]     An imaging apparatus according to this invention includes: an imaging means for photographing an object, thereby to generate a video signal; a pattern-generating means for generating a two-dimensional gradation pattern; and a multiplying means for multiplying the video signal by a gain that corresponds to the two-dimensional gradation pattern.  
         [0014]     In the imaging apparatus according to the present invention, it is possible to change a rate at which the two-dimensional gradation pattern generated in the pattern-generating means changes in gradation.  
         [0015]     In the imaging apparatus according to the present invention, it is possible to change the two-dimensional gradation pattern generated in the pattern-generating means.  
         [0016]     In a method of processing images, according to the invention, a video signal generated by photographing an object is multiplied by a gain that corresponds to a two-dimensional gradation pattern, thereby to reduce a difference in brightness between the parts of the image represented by the video signal.  
         [0017]     An imaging apparatus according to this invention includes: a color imaging means for photographing an object, thereby to generate a color video signal; a pattern-generating means for generating a two-dimensional gradation pattern; and a multiplying means for multiplying the color components of the video signal by a gain that corresponds to the two-dimensional gradation pattern.  
         [0018]     In a method of processing images, according to the present invention, color components of a color video signal generated by photographing an object are multiplied by a gain that corresponds to a two-dimensional gradation pattern, thereby to change the white balance of an image represented by the color video signal.  
         [0019]     The present invention can provide an image that can be well recognized visually, because if the image has parts, which much differ in brightness, the difference in brightness between these parts is reduced. In addition, the dynamic range of the image or the compression ratio can be changed, without performing a mechanical operation such as the attaching or rotating of a filter. Moreover, the white balance of the image can be changed in accordance with a specific pattern, thus emphasizing the blue of the sky part of the image. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]      FIG. 1  is a block diagram illustrating the configuration of an imaging apparatus according to the present invention;  
         [0021]      FIG. 2  is a block diagram depicting the configuration of the dynamic-range compressing unit provided in the imaging apparatus;  
         [0022]      FIG. 3  is a diagram showing a gradation pattern generated by the fixed-pattern generating unit of the dynamic-range compressing unit;  
         [0023]      FIG. 4  is a block diagram illustrating the fixed-pattern generating unit of the dynamic-range compressing unit;  
         [0024]      FIG. 5  is a diagram schematically showing how a gradation pattern generated by the fixed-pattern generating unit changes;  
         [0025]      FIG. 6  is a diagram schematically showing some gradation patterns that the fixed-pattern generating unit selectively generates; and  
         [0026]      FIG. 7  is a block diagram depicting another configuration that the dynamic-range compressing unit may have. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]     An embodiment of this invention will be described in detail, with reference to the accompanying drawings. The invention is not limited to the embodiment that will be described below. Various changes and modifications can of course be made, without departing from the scope and spirit of this invention.  
         [0028]     The present invention is applied to, for example, an imaging apparatus  100  that is configured as shown in  FIG. 1 .  
         [0029]     The imaging apparatus  100  includes an imaging unit  10 , a signal-correcting unit  20 , a dynamic-range compressing unit  30 , and a camera-signal processing unit  40 . The imaging unit  10  has a solid-state imaging element, such as a charge-coupled device (CCD). The unit  10  photographs an object, generating a video signal that represents the image of the object. The video signal is supplied to the signal-correcting unit  20 . The unit  20  performs a correction process on, for example, the shading component of the video signal. The video signal thus processed is supplied to the dynamic-range compressing unit  30 . The unit  30  compresses the dynamic range of the video signal, which is supplied to the camera-signal processing unit  40 . The camera-signal processing unit  40  performs a process, such as gamma correction, on the video signal. The video signal thus processed is supplied to a recording system such as a VTR or to a display system  50 .  
         [0030]     The dynamic-range compressing unit  30  has the configuration illustrated in the block diagram of  FIG. 2 . As  FIG. 2  shows, this unit  30  includes a pattern-generating unit  31  and three multipliers  32 R,  32 G and  32 B. The pattern-generating unit  31  generates a two-dimensional gradation pattern. The multipliers  32 R,  32 G and  32 B receive video signals Rin, Gin and Bin from the signal-correcting unit  20  and gain coefficients R_GAIN, G_GAIN and B_GAIN from the pattern-generating unit  31 . Note that the gain coefficients R_GAIN, G_GAIN and B_GAIN correspond to the two-dimensional gradation pattern. The multipliers  32 R,  32 G and  32 B multiply the video signals by gain coefficients R_GAIN, G_GAIN and B_GAIN.  
         [0031]     The pattern-generating unit  31  includes a fixed-pattern generating unit  31 A and a gain-converting unit  31 B. The fixed-pattern generating unit  31 A generates such a two-dimensional fixed pattern as shown in  FIG. 3 . The gain-converting unit  31 B converts the levels of the parts of the fixed pattern to gain coefficients. For example, any white part of the pattern is converted to a gain coefficient of ×1.0 and any black part to a gain coefficient of ×0.5. Thus, the unit  31 B outputs gain coefficients R_GAIN, G_GAIN and B_GAIN.  
         [0032]     As  FIG. 4  shows, the fixed-pattern generating unit  31 A includes an H-gradation-pattern generating unit  311 , a V-gradation-pattern generating unit  312 , a pattern-mixing unit  313  composed of an H-gradation-pattern and V-gradation-pattern, and an output selector  314 .  
         [0033]     The H-gradation-pattern generating unit  311  is a module that generates a one-dimensional gradation pattern for the horizontal direction. It includes a memory  311 A and a line-pattern generator  311 B. The memory  311 A holds gradation data for the horizontal direction. The line-pattern generator  311 B generates an address in the memory  311 A, reads data from the memory  311 A, calculates a gradation level from the data, and outputs the gradation level. The gradation pattern consists of 32 broken lines. The memory  311 A stores the data representing the inclination of each broken line and the data representing each segment of the pattern.  
         [0034]     The V-gradation-pattern generating unit  312  is a module that generates a one-dimensional gradation pattern for the vertical direction. It includes a memory  312 A and a line-pattern generator  312 B. The memory  312 A holds gradation data for the vertical direction. The line-pattern generator  312 B generates an address in the memory  312 A, reads data from the memory  312 A, calculates a gradation level from the data, and outputs the gradation level. The gradation pattern consists of 32 broken lines. The memory  311 A stores the data representing the inclination of each broken line and the data representing each segment of the pattern.  
         [0035]     In the H-gradation-pattern generating unit  311  and V-gradation-pattern generating unit  312 , the data items h_grad—count_step and v_grad_count_step set for the change rate of the H- and V-gradation patterns that should be given to the line-pattern generators  311 B and  312 B, respectively, are changed. The H-gradation and V-gradation can thereby be increased or decreased in terms of gradation, without changing the contents of the memories  311 A and  312 A, as illustrated in  FIGS. 5A, 5B  and  5 C.  
         [0036]     The H-gradation-pattern generating unit  311  and the V-gradation-pattern generating unit  312  can set offset positions for the H- and V-gradation patterns, respectively, in accordance with the offset data items h_grad_offset and v_grad_offset given to the line-pattern generators  311 B and  312 B. The pattern can therefore move horizontally (H) and vertically (V) by the distance corresponding to the number of pixels set.  
         [0037]     The H-gradation-pattern generating unit  311  and the V-gradation-pattern generating unit  312  can set angles through which the H- and V-gradation patterns should be rotated, respectively, in accordance with the rotation parameters h_grad_rotate and v_grad rotate given to the line-pattern generators  311 B and  312 B. The patterns are not actually rotated, nevertheless. The positions in the memories  311 A and  312 A, where the reading of data is started, are shifted for each line, thereby changing the offset values. These offset values are set in accordance with the rotation parameters.  
         [0038]     The rotation parameters and the offset values are combined with the inversion of pattern described below. This makes it possible to rotate the gradation pattern through 360°, without rewriting the content of the memory  311 A or that of the memory  312 A.  
         [0039]     The H-gradation-pattern generating unit  311  and the V-gradation-pattern generating unit  312  can invert the white/black levels of the H- and V-gradations in accordance with the inversion parameters h_grad_inv and v_grad_inv supplied to their line-pattern generators  311 B and  312 B, respectively. When the level of H-gradation is inverted, the output pattern is inverted left side right. When the level of V-gradation is inverted, the output pattern is inverted upside down.  
         [0040]     The pattern-mixing unit  313  is a module that mixes the H-gradation pattern and the V-gradation pattern, generating a mixed gradation pattern. The pattern-mixing unit  313  includes an adder  313 A, a multiplier  313 B, and a divider  313 C. The adder  313 A and the multiplier  313 B receive the H- and V-gradation patterns from the H- and V-gradation-pattern generating units  311  and  312 . The divider  313 C divides the output of the adder  313 A by 2 (two), finding the average of the outputs of the adder  313 A.  
         [0041]     The output selector  314  is a module that selects a pattern in which the H- and V-gradations will be mixed, in accordance with selection data grad_hv_sel. It can select and output one of an H-gradation pattern, a V-gradation pattern, a (H+V)/2 gradation pattern and an H×V gradation pattern, which are illustrated in  FIGS. 6A, 6B ,  6 C and  6 D, respectively, supplied through the pattern-mixing unit  313 .  
         [0042]     The gain-converting unit  31 B receives the fixed pattern GRAD_PATTERN from the fixed-pattern generating unit  31 A and converts the fixed pattern into gain coefficients R_GAIN, G_GAIN, and B_GAIN for R, G and B gradation patterns, respectively. For the two-dimensional R gradation, for example, any part of the fixed pattern GRAD_PATTERN, which is white, is converted to R_GRAD_ND_HI, and any part thereof, which is black, is converted to R_GRAD_ND_LO. The gain coefficients R_GAIN, G_GAIN, and B_GAIN, thus obtained, are applied. R_GRAD_ND_HI and R_GRAD_ND_HO are subjected to α-blending, in accordance with the level of the fixed pattern, providing a signal at a level intermediate between the white level and the black level of the fixed pattern.  
         [0043]     The gain-converting unit  31 B sets an attenuation rate for each of the R, G and B channels.  
         [0044]     The multipliers  32 R,  32 G and  32 B receive the video signals Rin, Gin and Bin from the signal-correcting unit  20  and multiply them by gain coefficients R_GAIN, G_GAIN and B_GAIN, which correspond to the two-dimensional gradation pattern that the pattern-generating unit  31  has generated. Thus, the dynamic-range compressing unit  30  compresses the dynamic range of the image.  
         [0045]     In the dynamic-range compressing unit  30  of the imaging apparatus  10 , the multipliers  32 R,  32 G and  32 B receive the video signals Rin, Gin and Bin from the imaging unit  10  that has photographed the object, and multiply these video signals by the gain coefficients R_GAIN, G_GAIN and B_GAIN that correspond to the two-dimensional gradation pattern that the pattern-generating unit  31  has generated. The dynamic-range compressing unit  30  can therefore reduce the difference in brightness between the images represented by the video signals Rout, Gout and Bout output from the multipliers  32 R,  32 G and  32 B. Thus, the function of an optical half-ND filter is realized by the electrical processing.  
         [0046]     In the dynamic-range compressing unit  30 , the rate at which to change the gradation of the two-dimensional gradation pattern generated by the pattern-generating unit  31  can be changed, and the two-dimensional gradation pattern can be changed. Thus, the gradation of the image can be compressed in accordance with the two-dimensional distribution of luminance in the image.  
         [0047]     In the dynamic-range compressing unit  30 , the gain-converting unit  31 B may change the video signals Rin, Gin and Bin to different values. In this case, the white balance of the image can be adjusted in accordance with the fixed pattern generated by the fixed-pattern generating unit  31 A.  
         [0048]     Hence, if the upper part of the image is the sky, the blue of the sky can be emphasized by decreasing only gain coefficients R_GAIN and G_GAIN.  
         [0049]     The dynamic-range compressing unit  30  may, of course, have such a configuration as illustrated in  FIG. 7 . That is, the unit  30  may include fixed-pattern generating units  31 Ar,  31 Ag and  31 Ab and gain-converting units  31 Br,  31 Bg and  31 Bb, for R, G and B, respectively. This dynamic-range compressing unit is larger in circuit scale than the dynamic-range compressing unit  30  shown in  FIG. 2 . Nonetheless, an R pattern, a G pattern and a B pattern can be generated independently. This makes it possible to adjust the white balance in the image more flexibly.  
         [0050]     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alternations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.