Abstract:
The present invention relates to electronic cameras including solid state imaging devices. More particularly, the present invention relates to circuits and techniques for indication of the quality of recorded images. An electronic camera has a solid state imaging device, a memory for storage of images recorded with the imaging device, and a controller that is adapted to store an image quality parameter value together with a respective image.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to electronic cameras including solid state imaging devices, such as CCDs, CMOS sensors, etc. More particularly, the present invention relates to circuits and techniques for indication of the quality of recorded images.  
         [0003]     2. Description of the Related Art  
         [0004]     Electronic cameras including solid state imaging devices, such as CCDs, CMOS sensors, etc., are well known in the art. The solid state imaging device has an array of a large number of light sensitive detectors, each of which records the light energy incident on the detector during an exposure period. For example, in a CCD a charge is formed in each detector of the CCD that is proportional to the light energy incident on the detector during an integration period. The recorded light energy values of the detectors are read out of the solid state device and are typically converted to a digital value, forming a digital representation of the recorded image. Each detector represents a pixel of the image, and the pixel value is equal to the digitised recorded light energy value of the corresponding detector.  
         [0005]     Thus, the recorded image is divided into a large number of segments, i.e., pixels, with allocated digital values as pixel values. For example, a grey tone image may be represented digitally by pixels with one respective pixel value representing the grey tone of the corresponding pixel. Similarly, a color image may be represented by pixels having three respective pixel values, one for each of the colors red, green, and blue.  
         [0006]     In the present context, the term exposure is to be understood in a broad sense as the time period during which an energy sensor is actually sensing the energy. For example, a photographic film is exposed to light whenever light is incident upon it, while a CCD is exposed to light when the pixel elements of the CCD are allowed to integrate light incident upon them.  
         [0007]     A color filter mask may overlay the CCD array such that each light sensitive pixel element in the CCD-array may be covered with a color filter for passing light within a specific wavelength range corresponding to a specific primary color, typically red, green and blue. The color filter mask allows a color image to be recorded in a single exposure at the expense of resolution.  
         [0008]     Focus and exposure of an electronic camera may be automatically adjusted in order to record an image with optimum settings. An indication of the quality of the image having been recorded may be provided to the photographer.  
         [0009]     The selection of the best images from a professional photographer&#39;s photo session has always been a key to the success of the photographer. Using a conventional photographic film camera, the selection is performed based on film strips positioned on a light table and based on contact sheets with prints of the recorded images.  
         [0010]     Using current electronic cameras, the photographer typically takes many more photographs or images than with a conventional film camera. Since no photographic film is consumed, an extra image or extra  100  images may be recorded without added cost of film, processing, contact sheet printing, etc. This encourages the photographer to take many more photos than with conventional film cameras e.g. from a larger number of different angles and distances and with a larger number of different light settings.  
         [0011]     Therefore the process of selecting the best images from a photo session becomes a demanding task.  
       SUMMARY OF THE INVENTION  
       [0012]     The present invention is therefore directed to an electronic camera, which overcomes one or more of the problems of the related art.  
         [0013]     It is a feature of an embodiment of the present invention to provide an electronic camera with functions facilitating the above-mentioned task of selecting the best images from a set of recorded images.  
         [0014]     According to the invention, the above-mentioned and other features are fulfilled by an electronic camera with an object lens for focusing an image of an object onto an image plane, and a solid state imaging device positioned at the image plane for conversion of the image into electrical signals, and a controller that is adapted to store an image quality parameter value together with electrical signal values of a respective image.  
         [0015]     Preferably, the controller is adapted to store an image quality parameter value together with electrical signal values of a respective image in combination with the image for subsequent access of the combination for comparison of a plurality of combinations.  
         [0016]     The electronic camera may be a still camera or a video camera.  
         [0017]     The solid state imaging device and the controller and associated circuitry may reside in a camera back (sometimes denoted a digital camera back) that attaches like a conventional photographic film holder to a conventional camera.  
         [0018]     Preferably, the electronic camera includes a display for displaying recorded images together with a symbol indicating its image quality parameter value.  
         [0019]     Preferably, the electronic camera further includes a user interface with a user interface element, such as a key, a button, a switch, a touch screen area, voice recognition, etc., for user selection of an image quality parameter value for storage with the respective image.  
         [0020]     The recorded images may be divided into a set of quality categories according to their quality parameter values. The images of a specific quality category may, e.g., have a specific image quality parameter value (e.g., 1, 2, 3, . . . ) defining the category in question, or, the quality parameter value of images in a specific category may reside within predetermined limits defining the category in question, etc.  
         [0021]     The camera controller may for example be adapted to store each recorded image in the camera image memory, e.g., a memory card, together with the highest possible image quality parameter value immediately upon exposure. The photographer may then evaluate the image by viewing a display of the image, preferably on a display of the camera. The photographer may decide that the recorded image is a top quality image and thus, leave the stored image quality parameter value unchanged, or, the photographer may decide that the recorded image is of a lower quality and therefore operate the user interface element for selection of a lower image quality parameter value for storage together with the image in question, thereby moving the image to a lower quality category.  
         [0022]     The camera may for example be adapted to classify recorded images into three different categories, such as a “good” category, a “bad” category, and an “in between” category. Naturally, many more categories may be contemplated.  
         [0023]     The controller may further be adapted to calculate an image quality parameter value for a recorded image based on recorded image intensities.  
         [0024]     The controller may be adapted for calculation of the quality parameter value of a recorded image based on any image parameter, such as luminance, brightness, contrast, color balance, white balance, focus, etc., or any combination hereof.  
         [0025]     The controller may further be adapted for calculation of the quality parameter value of a recorded image based on one or more histograms of pixel values of the recorded image, e.g., one or more of red, green, and blue intensity values of the pixels, or, one or more corresponding values of another color filter utilized in the color filter mask of the solid state imaging sensor.  
         [0026]     In an embodiment of the present invention, the controller may be adapted to calculate a plurality of image quality parameters, such as two, three, or more image quality parameters.  
         [0027]     Preferably, the electronic camera further includes a light meter in which case, the controller may further be adapted to calculate an image quality parameter value for a recorded image based on a respective light meter reading and recorded image intensities, e.g., based on a comparison between the light meter reading and recorded image intensities.  
         [0028]     For example, the camera may include a light meter for measurement of the intensity of light emerging from a small sized area at the centre of the viewing field of the camera. This intensity measurement may be compared with recorded light intensities integrated across a corresponding area of the solid state imaging device. If the difference is within predetermined threshold values, the recorded image is assigned the best quality parameter value. If the difference is larger than the predetermined threshold values, the recorded image is assigned the second best quality parameter value. A plurality of threshold values or threshold value intervals may be defined corresponding to a plurality of image quality categories.  
         [0029]     Further the camera may include a light meter for measurement of an average intensity of light emerging from a significant part of the viewing field of the camera. This intensity measurement may be compared with recorded light intensities integrated across a corresponding area of the solid state imaging device. Preferably, the controller also applies the weighing function of the light meter during the integration of the corresponding area of the solid state imaging device. If the difference is within predetermined threshold values, the recorded image is assigned the best quality parameter value. If the difference is larger than the predetermined threshold values, the recorded image is assigned the second best quality parameter value. A plurality of threshold values or threshold value intervals may be defined corresponding to a plurality of image quality categories.  
         [0030]     Both comparisons may be combined so that a recorded image is assigned the best quality parameter value when both differences are less than the respective smallest threshold values.  
         [0031]     The camera may also include an auto-focus device with an output signal indicating whether the auto-focus device has been able to focus the image or not. The controller may be adapted to incorporate the value of the auto-focus output signal into the calculated image quality parameter value, e.g., the recorded image quality parameter value may be reduced if the auto-focus device has not been able to focus the image, e.g., whereby the image may be moved from one quality category to the next lower quality category.  
         [0032]     The controller may be adapted to compare successive readings from the auto-focus device, and if the successive readings deviate, i.e., if the difference between successive readings lies outside predetermined limits, the recorded image quality parameter value may be reduced, e.g. whereby the image may be moved from one quality category to the next lower quality category.  
         [0033]     An appropriately focused recorded image contains large intensity gradients while a defocused image (blurred) has a more smooth intensity profile. Thus, the controller may be adapted to detect gradients in the recorded image and determine whether the recorded image is focused or not. This determination may be compared with the output of the auto-focus device. For example, if the difference is within predetermined threshold values, the record image is assigned the best quality parameter value. If the difference is larger than the predetermined threshold values, the recorded image is assigned the second best quality parameter value. A plurality of threshold values may be defined corresponding to a plurality of image quality categories.  
         [0034]     The focus and light meter comparisons may be combined so that a recorded image is assigned the best quality parameter value when both differences are less than the respective smallest threshold values.  
         [0035]     In another embodiment, the controller is adapted to incorporate the comparison into the determination of the image quality parameter value by reducing the image quality parameter value if the difference is larger than the predetermined threshold, e.g., whereby the image may be moved from one quality category to the next lower quality category.  
         [0036]     The camera may further include camera monitoring circuitry outputting indicator signals of the performance of the camera. For example, the camera may include circuitry monitoring the operation of the flashlight and signalling whether the flashlight fired during image recording or not. The signal may tell whether the flashlight was not charged properly or whether the flashlight is simply not functioning at all. The camera monitoring circuitry may further include a circuit for monitoring the status of one or more batteries in the camera, the operation of the camera shutter, etc.  
         [0037]     The controller may further be adapted to incorporate the output signals of camera monitoring circuitry in the calculated image quality parameter value by reducing the image quality parameter value whenever an output signals a malfunction or a non-optimal performance.  
         [0038]     The controller may signal an indication of the calculated quality of a recorded image to the user of the camera.  
         [0039]     One or more of the calculated image parameter values may be displayed to the operator of the camera, e.g., in the viewer of the camera. Preferably, however, a warning is displayed when the calculated image quality parameter value does not belong to the top quality category.  
         [0040]     In a preferred embodiment of the present invention, the camera includes a sound reproducing element that is controlled by the controller for emission of an audible sound when at least one of the quality parameters is outside a predetermined desirable range. The audible sound may, e.g., be a single distinct sound (“bip”) of a specific frequency, a modulated sound, a swept sound, a series of distinct sounds of a specific frequency or of different frequencies, such as a tune, etc, as is well-known in the art of mobile telephones.  
         [0041]     A plurality of distinguishable sounds may be related to specific respective qualities of the image. For example, a sound swept from a low frequency to a high frequency may signal that the recorded image is over-exposed while a sound swept from a high frequency to a low frequency may signal that the recorded image is under-exposed.  
         [0042]     The camera may further include automatic adjustment means for adjustment of the camera in response to the calculated quality parameters so that a new image recording may be performed with optimum settings of the camera. For example, the camera objective may be focused based on the calculated focus parameter, or a diaphragm may be adjusted in response to the calculated brightness.  
         [0043]     The camera may further include a selector for user selection of a part of the image, and wherein the quality parameter is calculated based solely on electrical signals from pixels within the selected part of the image. Hereby, the operator of the camera may select a part of the viewing field to form basis for the quality parameter determination, e.g., a central part of the viewing field.  
         [0044]     As already mentioned, the user of the camera may manually modify the image quality parameter value of a recorded image either immediately upon recording of the image, or, at any time later after storage of the image in the memory. The user may increase the quality parameter value, e.g., whereby the image in question is moved to a better image quality category, or, the user may decrease the quality parameter value, e.g., whereby the image in question is moved to a lower image quality category. The controller may further be adapted to store a symbol indicating whether the user of the camera has adjusted the stored image quality parameter value or the stored image quality parameter value has been set by the camera controller.  
         [0045]     When the image memory of the camera is full, the controller may further be adapted to automatically delete an image with the lowest quality parameter value upon recording of a new image in order to free memory space for storage of the new image.  
         [0046]     The electronic camera may further include a computer interface, and the controller may be adapted to transfer images together with their respective image quality parameter values from the memory to a computer, e.g., via the interface, or by moving a memory card from the camera to a memory card reader of the computer, etc.  
         [0047]     The controller may reside in the camera, or in the camera backplane, or, the controller may reside remotely from the camera, for example in a remote control unit or a computer that controls the camera through an interface, e.g., a wireless interface. Further, the controller may be divided into separate controllers, each of which performs a part of the controlling process of the controller, and each of which may reside in the camera, or in the camera backplane, or, remotely from the camera, for example in the remote control unit or the computer.  
         [0048]     In a preferred embodiment, the quality parameter value forms a part of the image file name. This makes the quality parameter feature of the camera compatible with any computer application relating to photography without modification of the application software. Thus, the quality parameter value of an image is available as a part of the file name of the image for use during the photographer&#39;s selection and finishing process.  
         [0049]     In another embodiment, the quality parameter value is provided as a tag in the image file, e.g., as metadata, or, the quality parameter value may be provided in the pixel data. In yet another embodiment, the quality parameter value is provided in a separate file.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0050]     The above and other features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:  
         [0051]      FIG. 1  illustrates a block diagram of an electronic camera according to an embodiment of the present invention;  
         [0052]      FIG. 2  illustrates a part of the user interface of a digital camera according to an embodiment of the present invention;  
         [0053]      FIG. 3  illustrates a displayed of the user interface of  FIG. 2  in more detail including a symbol indicating image quality;  
         [0054]      FIG. 4  illustrates a software light table with images displayed together with their respective symbols indicating their image quality parameter values;  
         [0055]      FIG. 5  illustrates a grey-scale image; and  
         [0056]      FIG. 6  illustrates a histogram of the grey-scale image of  FIG. 5 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0057]     Danish Patent Application No. PA 2005 00976, filed on Jun. 30, 2005, in the Danish Intellectual Property Office, and entitled: “Electronic Camera with Classification of Images According to Image Quality,” is incorporated by reference herein in its entirety.  
         [0058]     The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are illustrated. The invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.  
         [0059]     In the figures, the dimensions of layers and regions may be exaggerated for clarity of illustration. It will also be understood that when a layer or element is referred to as being “on” another layer or substrate, it can be directly on the other layer or substrate, or intervening layers may also be present. Further, it will be understood that when a layer is referred to as being “under” another layer, it can be directly under, and one or more intervening layers may also be present. In addition, it will also be understood that when a layer is referred to as being “between” two layers, it can be the only layer between the two layers, or one or more intervening layers may also be present. Like reference numerals refer to like elements throughout.  
         [0060]     The operational principles of the invention will now be explained with reference to  FIG. 1 .  FIG. 1  illustrates a block diagram of an electronic camera  10  according to the present invention. A movable object lens  12  may focus an image of an object (not shown) in co-operation with second lens  14  onto an image plane  16 , which coincides with the light sensitive surfaces of the array of light sensitive sensors of the CCD  18 . The image recording of the CCD  18  may be controlled by a CCD driver  20  that enables and disables integration of light by the CCD light sensors. The CCD driver  20  may also control shifting of the accumulated charges out of the CCD  18 , thereby forming electrical signals  19 . The electrical signals  19  may be received by a controller  22  that may compose a digital image based on the electrical signals  19 , provide a quality parameter value of the image and store the electrical signals  19  of an image together with the respective image quality parameter value in a memory  24 . The memory  24  may reside in a memory card that is inserted into a slot in the camera or camera back.  
         [0061]     A movable mirror  26  deflects part of the light from the camera lenses  12 ,  14  towards a light meter  28  and part of the light towards an auto-focusing device  27 . During exposure, the mirror  26  may be tilted as indicated by the arrow, allowing the light to pass to the CCD  18 . The time delay between the measurements performed by the light meter  28  and the auto-focusing device  27  and the actual recording of the image may cause discrepancies between the measurements and corresponding parameters calculated from the recorded image. Such discrepancies may indicate that the quality of the recorded image is less than optimal. This will be indicated by the illustrated embodiment based on the above-described comparisons performed by the controller  22  of the camera  10 .  
         [0062]     The controller  22  may reside in the camera  10 , or in the camera backplane, or, the controller  22  may reside remotely from the camera  10 , for example, in a remote control unit or a computer that controls the camera through an interface, e.g. a wireless interface. Further, the controller  22  may be divided into separate controllers, each of which performs a part of the controlling process of the controller  22 , and each of which may reside in the camera, in the camera backplane, or, remotely from the camera.  
         [0063]     Based on a focus parameter value provided by the auto-focusing device  27 , a lens drive motor  30  may be controlled by the controller  22  to move the objective lens  12  to focus the image. Based on a brightness parameter value provided by the light meter  28 , a diaphragm drive motor  32  may be controlled by the controller  22  to adjust the aperture of the diaphragm  34 . The integration time period determined by the CCD driver  20  of the CCD  18  may be controlled by the controller  22  for optimum exposure of the next image. The controller  22  may further be adapted to calculate an image quality parameter value for a recorded image based on recorded image intensities, light meter readings, focus readings, and values of signals from monitoring of the performance of the camera by camera monitoring circuitry  25 .  
         [0064]     The camera monitoring circuitry  25  may output indicator signals of the performance of the camera. For example, the camera monitoring circuitry  25  may monitor the operation of the flash and signal whether or not the flash fired during image recording. If there was no flash, the signal may indicate whether the flash was not charged properly or whether the flash is simply not functioning at all. The camera monitoring circuitry  25  may further include a circuit for monitoring the status of one or more batteries in the camera, the operation of the camera shutter, etc.  
         [0065]     A warning signal may be displayed in a field  36  of the viewer when one of the calculated quality parameters are outside predetermined respective desired ranges. When the image memory  24  of the camera  10  is full, the controller  22  may further automatically delete an image with the lowest quality parameter value upon recording of a new image in order to free memory space for storage of the new image.  
         [0066]     The camera  10  may further have a sound reproducing element  38  that may be controlled by the controller  22  for emission of an audible sound when at least one of the quality parameters is outside a predetermined desirable range. The audible sound may, e.g., be a single distinct sound (“bip”) of a specific frequency, a modulated sound, a swept sound, a series of distinct sounds of a specific frequency or of different frequencies, such as a tune, etc, as is well-known, e.g., in the art of mobile telephones. A plurality of distinguishable sounds may be related to specific respective qualities of the image. For example, a sound swept from a low frequency to a high frequency may signal that the recorded image is over-exposed while a sound swept from a high frequency to a low frequency may signal that the recorded image is under-exposed.  
         [0067]     The electronic camera  10  may further include a computer interface  23 , and the controller  22  may be adapted to transfer images with their respective image quality parameter values from the memory to a computer through the interface  23 .  
         [0068]      FIG. 2  illustrates part of a user interface of a digital still camera, including a display  40 .  FIG. 3  illustrates a detailed view of the display  40 . As can be seen in  FIGS. 2 and 3 , the display  40  may display recorded images  42  and a quality indicator  44  indicating its image quality parameter value. The user interface may include a user interface element  46  for user selection of an image quality parameter value for storage with the respective image.  
         [0069]     In the illustrated embodiment, the recorded and stored images may be classified into three different categories: 1) top quality, 2) middle quality, and 3) low quality. The corresponding image quality parameter value may be 1 for the top quality category, 2 for the middle quality category, and 3 for the low quality category.  
         [0070]     As shown in  FIG. 3 , the quality indicator  44  may include three circles linearly arranged adjacent to one another. For an image belonging to category 1 (top quality), a left most circle  48  of the symbol  44  may be green while the other circles, viz., a middle circle  50  and a right most circle  52  may be grey. For an image belonging to category 2 (middle quality), the middle circle  50  of the indicator  44  may be yellow. Finally, for an image belonging to category 3 (low quality), the right most circle  52  of the indicator  44  may be red.  
         [0071]     If the stored image quality parameter value has been adjusted by the user of the camera, the colored circle  48 ,  50 ,  52  of the indicator  44  also may indicate manual operation, e.g., by displaying a capital “M”. If the stored image quality parameter value has been set by the controller  22  of the camera  10  without user intervention, the colored circle  48 ,  50 ,  52  also may indicate automatic operation e.g., by displaying a capital “A”.  
         [0072]     In an embodiment, a file naming protocol of an image may include the stored image quality parameter and an indicator indicating if the image quality parameter has been manually or automatically set. An exemplary file name may be: “Pic001 M1.jpg”, where “M” indicates manual setting of the image quality parameter, and the digit “1” after “M” indicates that the picture Pic001 is top quality. Other examples may be: “Pic105 A3.jpg” indicating that the image quality parameter of picture Pic105 is automatically set and the picture is low quality.  
         [0073]     When the quality parameter value forms a part of the image file name, the quality parameter feature of the camera  10  may compatible with any computer application relating to photography without modification of the application software. Thus, the quality parameter value of an image is available as a part of the file name of the image for display together with the respective images making selection of images easier and faster. Alternatively, the quality parameter value may be provided as a tag in the image file, e.g. as metadata, or in the pixel data. In yet another embodiment, the quality parameter value may be provided in a separate file.  
         [0074]     The controller  22  of the camera  10  may be adapted to store each recorded image in the camera image memory together with the highest possible image quality parameter value (which is 1 (one) in this embodiment) immediately upon exposure. The photographer may then evaluate the image by viewing the image  42  on the display  40  of the camera  10 . The photographer may decide that the recorded image  42  is a top quality image and thus, leave the stored image quality parameter value 1 unchanged, or, the photographer may decide that the recorded image  42  is of a lower quality and therefore operate the actuator  46  for selection of a lower image quality parameter value for storage together with the image in question, thereby moving the image to a lower quality category, i.e., with an image quality parameter value equal to 2 or 3.  
         [0075]     The image quality category may be altered by manipulating the user interface element  46 . For example, pressing a right side of the user interface element  46  may move the displayed image  42  to the next lower category. Likewise, pressing a left side of the user interface element  46  may move the displayed image  42  to the next higher category. The quality category of an image may be changed whenever an image is displayed in the display  42  whether immediately upon recording of the image or at a later time upon retrieval of the image from the memory.  
         [0076]     The photographer may further select a part of the image for which the quality parameter is calculated based solely on electrical signals from pixels. Thus, the photographer of the camera may select a part of the viewing field as a basis for the quality parameter determination, e.g. a central part of the viewing field.  
         [0077]     As already mentioned, the controller  22  may further be adapted to calculate an image quality parameter value for a recorded image based on recorded image intensities, light meter readings, focus readings, and values of signals from monitoring of the performance of the camera by the camera monitoring circuitry  25 . If everything is as expected, the recorded image may be assigned to category 1 (top quality). However, if one of the above-mentioned readings is outside predetermined limits, the recorded image may be assigned to category 2 (middle quality).  
         [0078]      FIG. 4  illustrates a display window of such a software application displaying recorded images together with their respective symbols indicating image quality as previously described in connection with  FIG. 3 . For example, it is seen that the two upper left most images are of top quality (indicated by left most darkened dot  60 ), and the last image of the upper row is of middle quality (indicated by darkened middle dot  62 ). The left most image of the next row is of low quality (indicated by darkened most red dot  64 ), etc.  
         [0079]     As already mentioned, the image quality factors may be calculated from a histogram of a recorded image as illustrated in  FIGS. 5 and 6 . For example, in an over-exposed image, the histogram-distribution may move to the right and pixels will be missing at the low end of the histogram, and, in an under-exposed image, the histogram-distribution will move to the left and pixels will be missing at the high end of the histogram.  
         [0080]     In the illustrated embodiment, an image may be considered over-exposed if more than 5% of the pixels are over-exposed. An image may be considered under-exposed if the 95% percentile of pixel intensities is below half the maximum pixel intensity.  
         [0081]     Exemplary embodiments of the present invention have been disclosed herein, and although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. Accordingly, it will be understood by those of ordinary skill in the art that various changes in form and details may be made without departing from the spirit and scope of the present invention as set forth in the following claims.