Abstract:
An object of the present invention is to provide an image correcting apparatus capable of performing zoom processing or mask processing on an image output from an imaging device, such as an image display device or an image monitoring/recording device, or on a reproduced image from an image recorder, in such a way as to adjust the exposure or luminance of the zoomed portion or the unmasked portion of the image to an optimum level and thereby allow display of a clear image. 
     An image correcting apparatus of the present invention comprises: image input/output interfaces; zoom processing means for zooming an area of an input image; luminance histogram processing means for creating a luminance histogram of the zoomed area or an unmasked area of the image; and exposure correction processing means for adjusting the exposure or luminance of the zoomed area or the unmasked area to an appropriate level based on the luminance histogram created by the luminance histogram processing means.

Description:
CLAIM OF PRIORITY 
       [0001]    The present application claims priority from Japanese application serial No. JP 2006-159236, filed on Jun. 8, 2006, the content of which is hereby incorporated by reference into this application. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to image correcting apparatus. 
         [0004]    2. Description of the Related Art 
         [0005]    The prior art includes Japanese Laid-Open Patent Publication No. 5-244489 (1993). This publication states that a problem with conventional image display apparatuses for intercoms, monitoring cameras, etc. is that since the iris control is performed based on the luminance of the pixels in the entire imaging area, a portion of the screen display may not be clear or may not provide the details of the displayed object(s) (even if enlarged, or zoomed in) if there is a large difference between the luminance of that portion and the luminance of the entire imaging area. To solve this problem, the above publication discloses an image display apparatus that includes a zoom area luminance measuring unit for measuring the luminance of an area being zoomed and an iris control unit for controlling the iris based on the measured luminance. 
       SUMMARY OF THE INVENTION 
       [0006]    When a backlighted person by the window is photographed from inside a room using a video camera or an electronic still camera, or when a person in a room is photographed from outside the house using such a camera, the captured image of the person is underexposed and hence dark and unclear if ordinary exposure control is performed on the image, even though the image of the landscape outside is properly exposed. 
         [0007]    Even if the above captured image of the person is enlarged or subjected to zoom processing so as to zoom in on the person), the resultant image is still underexposed and appears too dark since the exposure control is performed based on the average luminance of the entire screen displayed before the zoom process. 
         [0008]    To allow an imaging apparatus to properly zoom an area of an image having spatial variations in luminance, some conventional exposure correcting techniques detect, or measure, the luminance of this zoom area and controls the iris of the apparatus based on the detected luminance so as to correct the exposure for the area. 
         [0009]    The technique disclosed in the above patent publication measures the luminance of an area to be zoomed in by use of a zoom area luminance measuring unit and then controls the iris of the imaging unit based on the measured luminance by use of an iris control unit, as described above. 
         [0010]    However, conventional techniques (such as that described above) that control the iris of the imaging unit are disadvantageous in that they cannot be applied to cameras with no iris control function. Further, the iris control unit (if employed) must be set within the same enclosure as the imaging unit, or it must be connected to the imaging unit if it is installed at a separate location, incurring additional costs, that is, the cost of the iris control unit and the cost of installing and connecting it, etc. For example, the cost associated with such iris control is significantly higher in the case of a monitoring system in which an image output from the camera is zoomed and displayed by a separate recorder. 
         [0011]    These problems must be overcome to properly perform zoom processing or mask processing on an output image or a reproduced image from an image display device or an image recorder at reduced cost. Thus, there is a need for a technique to optimize the exposure (or luminance level) of a zoomed image or an unmasked image to provide a clear image display. 
         [0012]    It is, therefore, an object of the present invention to provide an image correcting apparatus having enhanced performance. 
         [0013]    To achieve the above object, an exemplary aspect of the present invention provides an image correcting apparatus capable of extracting an area of an image represented by received image information (for example, through zoom processing or mask processing), creating a luminance histogram of the extracted area, and correcting the exposure or luminance level of the area based on this luminance histogram. 
         [0014]    It should be noted that the following description and the appended claims provide more detailed aspects of the present invention. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    These and other features, objects and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings wherein: 
           [0016]      FIG. 1  is a block diagram showing an image correcting apparatus according to a first embodiment of the present invention; 
           [0017]      FIG. 2  is a diagram showing an exemplary application of the image correcting apparatus of the first embodiment; 
           [0018]      FIG. 3  is a block diagram showing an image correcting apparatus according to a second embodiment of the present invention; 
           [0019]      FIG. 4  is a block diagram showing an image correcting apparatus according to a third embodiment of the present invention; 
           [0020]      FIG. 5  is a diagram showing an exemplary application of the image correcting apparatus according to the present invention; 
           [0021]      FIG. 6  is a block diagram showing an image correcting apparatus according to a fourth embodiment of the present invention; 
           [0022]      FIG. 7  is a block diagram showing an image correcting apparatus according to a fifth embodiment of the present invention; 
           [0023]      FIG. 8  is a diagram showing an exemplary application of an image correcting apparatus according to the present invention; and 
           [0024]      FIG. 9  is a flowchart showing an exemplary image correction processing flow according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    following are reference numerals used in the this specification.
         101  . . . image input I/F     102  . . . zoom processing means     103  . . . histogram processing means     104  . . . exposure correction processing means     105  . . . image output I/F     201  . . . input image     202  . . . zoom area within input image     203  . . . image that has been subjected to zoom processing     204  . . . image that has been subjected to zoom processing and exposure correction processing     301  . . . image input/IF     302  . . . zoom processing means     303  . . . histogram processing means     304  . . . exposure correction processing means     305  . . . image output I/F     306  . . . recording medium     401  . . . image input I/F     402  . . . mask processing means     403  . . . histogram processing means     404  . . . exposure correction processing means     405  . . . image output I/F     406  . . . recording medium     501  . . . input image     502  . . . image that has been subjected to mask processing     503  . . . image that has been subjected to mask processing and exposure correction processing     601  . . . image input I/F     602  . . . processor     603  . . . image output I/F     701  . . . image input I/F     702  . . . processor     703  . . . image output I/F     704  . . . recording medium     801  . . . image monitor     901  . . . zoom processing     902  . . . mask processing     903  . . . histogram processing     904  . . . exposure correction processing       
 
         [0062]    The present invention will now be described in detail with reference to the accompanying drawings. 
         [0063]    Preferred embodiments of the present invention will be described with reference to the accompanying drawings. 
         [0064]      FIG. 1  is a block diagram showing an image correcting apparatus according to a first embodiment of the present invention. 
         [0065]    Referring to the figure, reference numeral  101  denotes one or more image input interfaces (hereinafter referred to as image input I/F);  102 , a zoom processing means;  103 , a histogram processing means;  104 , an exposure correction processing means; and  105 , one or more image output interfaces (hereinafter referred to as image output I/F). 
         [0066]      FIG. 2  is a diagram showing images generated by performing zoom processing and exposure correction processing on an input image from a monitoring camera, etc. by use of the image correcting apparatus of the first embodiment. The input image shows a scene that includes a building wall with a door left open to partially reveal the inside of the building. The luminance of the wall, etc. outside is high while that of the inside of the building is low. That is, there is a large luminance difference between these objects, and the high luminance area in the image, or scene, is significantly larger than the low luminance area. 
         [0067]    Specifically, reference numeral  201  denotes the input image from a monitoring camera, etc., showing a building wall with a door left open to partially reveal the inside of the building, as described above. Reference numeral  202  denotes an image which is a result of adding to the image  201  a rectangle indicating an area to be subjected to zoom processing. Reference numeral  203  denotes an image generated by performing zoom processing on the indicated area. Reference numeral  204  denotes an image generated by performing exposure correction processing on the image  203  that has been subjected to the zoom processing. 
         [0068]      FIG. 3  is a block diagram showing an image correcting apparatus according to a second embodiment of the present invention. 
         [0069]    Referring to the figure, reference numeral  306  denotes a recording medium. Reference numerals  301  and  305  denote interfaces corresponding to the interfaces  101  and  105  shown in  FIG. 1 , respectively. Reference numerals  302  to  304  denote means corresponding to the means  102  to  104  shown in  FIG. 1 , respectively. 
         [0070]      FIG. 4  is a block diagram showing an image correcting apparatus according to a third embodiment of the present invention. Reference numeral  402  denotes a mask processing means. Reference numerals  401  and  405  denote interfaces corresponding to the interfaces  101  and  105  shown in  FIG. 1 , respectively. Reference numerals  402  to  404  denote means corresponding to the means  102  to  104  shown in  FIG. 1 , respectively. Reference numeral  406  denotes means corresponding to means  306  in  FIG. 3 . 
         [0071]      FIG. 5  is a diagram showing images generated by performing mask processing and exposure correction processing on an input image from a monitoring camera, etc. by use of the image correcting apparatus of the third embodiment. The input image shows a scene that includes a building wall with a door left open to partially reveal the inside of the building. The luminance of the wall, etc. outside is high while that of the inside of the building is low. That is, there is a large luminance difference between these objects, and the high luminance area in the image, or scene, is significantly larger than the low luminance area. 
         [0072]    Specifically, reference numeral  501  denotes the input image from a monitoring camera, etc., showing a building wall with a door left open to partially reveal the inside of the building, as described above. Reference numeral  502  denotes an image generated by performing mask processing on the input image  501 . Reference numeral  503  denotes an image generated by performing exposure correction processing on the image  502  that has been subjected to the mask processing. 
         [0073]    The operation of the image correcting apparatus of the first embodiment will now be described with reference to  FIG. 1 . The image input I/F  101  receives an image signal from, for example, a monitoring camera. It should be noted that when the monitoring camera captured this image signal, it performed exposure control based on the average luminance of the entire screen display or the luminance level of a particular portion thereof. The zoom processing means  102  performs zoom processing on an area of the input image signal. This area is specified manually or automatically. Then, the histogram processing means  103  creates a luminance histogram based on the image signal on which the zoom processing means  102  has performed the zoom processing. After that, based on histogram data received from the histogram processing means  103 , the exposure correction processing means  104  performs exposure correction on the image signal that has been subjected to the zoom processing. The image data or signal that has been subjected to the exposure correction is output to an external monitor, etc. through the image output I/F  105 . 
         [0074]      FIG. 2  shows exemplary images generated by the image correcting apparatus shown by the block diagram of  FIG. 1 . Referring to  FIG. 2 , the image  201  input to the image input I/F shows a scene that includes a building wall with a door left open to partially reveal the inside of the building, as described above. The luminance of the wall, etc. outside is high while that of the inside of the building is low. That is, the high luminance area in the scene, or image, is significantly larger than the low luminance area. In such a case, the exposure control is usually performed such that objects outside, such as the wall, are properly exposed, with the result that the inside of the building is underexposed. 
         [0075]    The image  202  includes a rectangle that indicates an area to be subjected to zoom processing or a zoom area. The zoom processing means  102  performs zoom processing on this area. 
         [0076]    Referring still to  FIG. 2 , the image  203  is a result of performing zoom processing on the above indicated area within the image  202 . It should be noted, however, that this zoomed image  203  showing the inside of the building is still underexposed since the exposure for this image is the same as that for the input image  201 , making it difficult to see what is inside the building. Thus, simply performing zoom processing on an image captured by a monitoring camera, etc. usually does not lead to a properly exposed zoomed image. 
         [0077]    To overcome this problem, the histogram processing means  103  shown in  FIG. 1  creates a histogram indicating the luminance distribution in the image  203 , and the exposure correction processing means  104  shown in  FIG. 1  corrects the luminance level of the image  203  so as to generate a properly exposed zoomed image (such as the image  204  shown in  FIG. 2 ). Thus, the present invention provides an image correcting apparatus capable of correcting a zoomed image such that the exposure or luminance of the image is at a proper level. 
         [0078]      FIG. 3  shows the image correcting apparatus of the second embodiment, as described above. This image correcting apparatus differs from that shown in  FIG. 1  in that it additionally includes a recording medium. 
         [0079]    Referring to  FIG. 3 , the image signal input to the image input I/F  301  is either subjected to zoom processing as in  FIG. 1  or stored on the recording medium  306 . When an image signal stored on the recording medium  306  is reproduced, the zoom processing means  302  performs zoom processing on a specified area of the image. Then, the exposure correction processing means  304  corrects the zoomed area such that the exposure or luminance of the area is at a proper level, as in the first embodiment. The image input to the image input I/F  301  and directly subjected to zoom processing is also processed in the same manner as in the first embodiment. 
         [0080]      FIG. 4  shows the image correcting apparatus of the third embodiment, as described above. This image correcting apparatus differs from that shown in  FIG. 3  in that it includes a mask processing means  402  instead of the zoom processing means  302 . 
         [0081]    Referring to  FIG. 4 , the image signal input to the image input I/F  401  is either subjected to mask processing or stored on the recording medium  406 , as in  FIG. 3 . When an image signal stored on the recording medium  306  is reproduced, the mask processing means  402  performs mask processing on a specified area of the image signal. It should be noted that this specification is done manually or automatically. 
         [0082]    Then, the histogram processing means  403  creates a luminance histogram of the unmasked area (not the masked area) of the image signal. Then, the exposure correction processing means  404  performs exposure correction on the image signal that has been subjected to the zoomed processing, based on the histogram indicating the luminance distribution in the unmasked area created by the histogram processing means  403 . After the above exposure correction processing, the resultant image data is output to an external monitor, etc. through the image output I/F  405 . 
         [0083]      FIG. 5  shows exemplary images generated by the image correcting apparatus shown by the block diagram of  FIG. 4 . In the image  501  in  FIG. 5 , the inside of the building is underexposed, as in the case of the input image  201  in  FIG. 2 . 
         [0084]    The image  502  is a result of performing mask processing on a specified area of the image  501 . In the image  502 , a shaded rectangle indicates the masked area. 
         [0085]    It should be noted, however, that the inside of the building in the image  502  that has been subjected to the mask processing is still underexposed since the exposure for this image is the same as that for the input image  501 , making it difficult to see what is inside the building. Thus, when an image captured by a monitoring camera, etc. is subjected to mask processing, the unmasked area of the image usually does not have an appropriate luminance level if ordinary exposure control has been used to capture the image, as in the first and second embodiments. 
         [0086]    To overcome this problem, the histogram processing means  403  shown in  FIG. 4  creates a histogram indicating the luminance distribution in the unmasked area of the image  502 , and the exposure correction processing means  404  shown in  FIG. 4  corrects the luminance level of the image  502  such that the exposure or luminance of the unmasked area is at a proper level. Thus, the present invention provides an image correcting apparatus capable of correcting an image having a masked portion such that the exposure or luminance of the image is at an appropriate level. 
         [0087]      FIG. 6  shows an image correcting apparatus according to a fourth embodiment of the present invention. This image correcting apparatus differs from that shown in  FIG. 1  in that it includes a processor  602  instead of the zoom processing means  102 , the histogram processing means  103 , and the exposure correction processing means  104  shown in  FIG. 1 . 
         [0088]    According to this embodiment, software in memory (not shown) causes the processor  602  to function as the zoom processing means  102 , the histogram processing means  103 , and the exposure correction processing means  104  shown in  FIG. 1 . Referring to the block diagram of  FIG. 6 , the processor  602  performs image correction on the image signal input to the image signal input I/F  601  such that the exposure or luminance of the image signal is at an appropriate level, as in  FIG. 1 . 
         [0089]      FIG. 7  shows an image correcting apparatus according to a fifth embodiment of the present invention. This image correcting apparatus differs from that shown in  FIG. 6  in that it additionally includes a recording medium. 
         [0090]    Referring to  FIG. 7 , when an image signal stored on the recording medium  704  is reproduced, the image correcting apparatus performs image correction on the image signal such that the exposure or luminance of the image signal is at an appropriate level, as in  FIG. 3 . 
         [0091]      FIG. 8  shows a split screen display made up of 4 sections each displaying a different image. 
         [0092]    The image correcting apparatus shown in  FIG. 1  may be adapted to be able to display a split screen made up of an appropriate number of sections and perform image correction processing on the image displayed on each section separately. This allows the image correcting apparatus to correct the exposure or luminance level of each image, as in  FIG. 1 . 
         [0093]    Although the split screen shown in  FIG. 8  is made up of 4 sections, a split screen including any number of sections may be used. Further, the image correcting apparatuses of the second to fifth embodiments also can be adapted to be able to display a split screen and perform image correction processing on the image displayed on each section of the screen separately. 
         [0094]      FIG. 9  is a flowchart showing a image correction process according to the present invention. 
         [0095]    This process includes both zoom processing  901  and mask processing  902 . However, either one of them may be omitted depending on the image correcting apparatus used. The image that has been subjected to zoom processing and/or mask processing is subjected to histogram processing  903 . Then, exposure correction processing  904  is performed on the image based on the results of the histogram processing or based on a created histogram to correct the image. 
         [0096]    It should be noted that in the above embodiments, the image input I/F and the image output I/F may handle either analog signals or digital signals. 
         [0097]    Thus, the present invention provides image correcting apparatuses having enhanced performance. 
         [0098]    While we have shown and described several embodiments in accordance with our invention, it should be understood that disclosed embodiments are susceptible to changes and modifications without departing from the scope of the invention. Therefore, we do not intend to be bound by the details shown and described herein but intend to cover all such changes and modifications as fall within the ambit of the appended claims.