JP2008066839A - Digital camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To generate image data of a size corresponding to the feature of the scene of a photographing object. <P>SOLUTION: The digital camera comprises: a memory for holding basic image data composed of the digital data of the maximum number of bits obtained by an A/D converter; a first histogram preparation means for preparing a basic histogram on the basis of the basic image data; a shrunk image generation means for generating shrunk image data indicating the gradation value of each pixel by the digital data of the reduced number of bits smaller than the maximum number of bits on the basis of the basic image; an expanded image generation means for generating expanded image data indicating the gradation value of each pixel constituting the shrunk image data by the digital data of the maximum number of bits; a second histogram preparation means for preparing a histogram on the basis of the expanded image data; an evaluation means for comparing the basic histogram with the reproduced histogram and evaluating the extent of influence on the feature of images by conversion to the shrunk image; and a recording control means for supplying the shrunk image data to the image recording processing of the poststage for the image for which the evaluated result indicating that the influence is little is obtained by the evaluation means. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention includes an analog / digital converter that generates image data having a number of bits larger than the number of bits compatible with a general image compression technique, and digital data obtained by such an analog / digital converter. The present invention relates to a digital camera having a function of recording image data composed of a storage medium on a storage medium.

In general, a digital camera performs image processing such as white balance correction and exposure correction on captured image data, compresses the correction result by image compression processing such as JPEG, and then stores it in a storage medium such as a compact flash card. It is recorded.
By applying an image compression technique such as JPEG, a large amount of image data can be recorded in a finite capacity of the storage medium, but a part of the information of the original image data is lost by the compression process. It is inevitable. Nonetheless, such a lack of information is rarely a problem when a general user takes and records a snapshot.

However, as the image quality of digital cameras has improved with the recent increase in the number of pixels of digital cameras and the number of professional and semi-professional users has increased, it is desirable to avoid the loss of information associated with compression processing as described above. It is supposed to be.
In order to meet such demands, a function of recording raw image data (so-called RAW data) composed of digital data obtained by A / D converting the output to an image sensor such as a CCD on a storage medium is provided. A digital camera has been proposed (see Patent Document 1).

In the RAW data recorded on the storage medium using such a function, all of the information captured by the CCD is held, so that the user can apply desired image processing to the RAW data. Image data representing an image with satisfactory image quality can be obtained. For example, even when the white balance of the entire image is shifted due to an output imbalance regarding each color component of the CCD, an appropriate white color can be obtained by adjusting the data of the corresponding color component included in the RAW data. It is possible to convert it into image data having a balance.
Japanese Patent Application Laid-Open No. 2001-223979

  By the way, since the above-mentioned RAW data corresponds to digital data obtained by an A / D converter, naturally, the data size of each image data becomes a size depending on the number of bits of the A / D converter. . And A / D converters equipped in digital cameras tend to become high bits every year, and the size of RAW data becomes very large along with this, so it is recorded on a storage medium such as a single compact flash card. The number of images that can be made is very small.

  On the other hand, depending on the characteristics of the scene to be photographed, sufficient image quality may be obtained even if the number of bits for A / D conversion is somewhat small. For such an image, recording a large size of RAW data obtained by high bit A / D conversion is a waste of a limited storage capacity. There is a need for a technique that enables a large amount of image data to be recorded on a storage medium.

  An object of the present invention is to provide a digital camera capable of generating image data representing a gradation value with digital data having an appropriate number of bits according to the characteristics of a scene to be photographed.

The principle of the first digital camera according to the present invention is as follows.
The A / D converter converts the gradation value indicated by the output signal of the image sensor into digital data having a predetermined maximum number of bits. The memory holds basic image data composed of digital data obtained by the A / D converter. The first histogram creating means creates a basic histogram indicating the frequency obtained by classifying the gradation value of each pixel constituting the basic image for each class according to the maximum number of bits based on the basic image data. The reduced image generating means generates reduced image data representing the gradation value of each pixel by digital data having a reduced bit number smaller than the maximum bit number, based on the basic image. The extended image generation means generates extended image data that represents the gradation value of each pixel constituting the reduced image data as digital data having the maximum number of bits. The second histogram creating means creates a histogram based on the extended image data, and performs a class interpolation on the histogram, thereby generating a reproduction histogram indicating the frequency of the gradation value in each class regarding the digital data having the maximum number of bits. Generate. The evaluation means compares the basic histogram and the reproduction histogram, and evaluates the magnitude of the influence that the conversion to the degenerated image has on the image characteristics. The recording control unit uses the degenerated image data for the subsequent image recording process for the image for which the evaluation result indicating that the influence is small is obtained by the evaluation unit.

The principle of the second digital camera according to the present invention is as follows.
The A / D converter converts the gradation value indicated by the output signal of the image sensor into digital data having a predetermined maximum number of bits. The memory holds basic image data composed of digital data obtained by the A / D converter. The first histogram creating means creates a basic histogram indicating the frequency obtained by classifying the gradation value of each pixel constituting the basic image for each class according to the maximum number of bits based on the basic image data. The reduced image generating means generates reduced image data representing the gradation value of each pixel by digital data having a reduced bit number smaller than the maximum bit number, based on the basic image. The extended image generation means generates extended image data that represents the gradation value of each pixel constituting the reduced image data as digital data having the maximum number of bits. The second histogram creating means creates a histogram based on the extended image data, and performs a class interpolation on the histogram, thereby generating a reproduction histogram indicating the frequency of the gradation value in each class regarding the digital data having the maximum number of bits. Generate. The evaluation means compares the basic histogram and the reproduction histogram, and evaluates the magnitude of the influence that the conversion to the degenerated image has on the image characteristics. The iterative control means replaces the basic image from which the evaluation result indicating that the influence is small by the evaluation means with a reduced image, and for this new basic image, a first histogram generating means, a reduced image generating means, an extended image generating means, The processing by the second histogram creation means and the evaluation means is started. The recording control means uses the basic image from which the evaluation result indicating that the evaluation means has a great influence is obtained for subsequent image recording processing.

The principle of the third digital camera according to the present invention is as follows.
The A / D converter converts the gradation value indicated by the output signal of the image sensor into digital data having a predetermined maximum number of bits. The memory holds basic image data composed of digital data obtained by the A / D converter. The first histogram creating means creates a basic histogram indicating the frequency obtained by classifying the gradation value of each pixel constituting the basic image for each class according to the maximum number of bits based on the basic image data. Based on the basic image, the reduced image generation means generates reduced image data representing the gradation value of each pixel using digital data having a reduced number of bits suitable for subsequent image processing including compression processing. The extended image generation means generates extended image data that represents the gradation value of each pixel constituting the reduced image data as digital data having the maximum number of bits. The second histogram creating means creates a histogram based on the extended image data, and performs a class interpolation on the histogram to generate a reproduction histogram indicating the frequency of the gradation value in each class regarding the digital data having the maximum number of bits. Generate. The evaluation means compares the basic histogram and the reproduction histogram, and evaluates the magnitude of the influence that the conversion to the degenerated image has on the image characteristics. The compression control unit uses the degenerated image data for subsequent image processing for an image for which an evaluation result indicating that the influence is small is obtained by the evaluation unit.

The principle of the fourth digital camera according to the present invention is as follows.
The A / D converter converts the gradation value indicated by the output signal of the image sensor into digital data having a predetermined maximum number of bits. The basic image acquisition means acquires basic image data composed of digital data obtained by the A / D converter in accordance with the draft mode output periodically output from the image sensor prior to photographing. The first histogram creating means creates a basic histogram indicating the frequency obtained by classifying the gradation value of each pixel constituting the basic image for each class according to the maximum number of bits based on the basic image data. The reduced image generating means generates reduced image data representing the gradation value of each pixel by digital data having a reduced bit number smaller than the maximum bit number, based on the basic image. The extended image generation means generates extended image data that represents the gradation value of each pixel constituting the reduced image data as digital data having the maximum number of bits. The second histogram creating means creates a histogram based on the extended image data, and performs a class interpolation on the histogram, thereby generating a reproduction histogram indicating the frequency of the gradation value in each class regarding the digital data having the maximum number of bits. Generate. The evaluation means compares the basic histogram and the reproduction histogram, and evaluates the magnitude of the influence that the conversion to the degenerated image has on the image characteristics. The bit number determining means determines the bit number of the image data corresponding to the scene to be photographed based on the evaluation result by the evaluating means. The conversion control unit instructs the A / D converter to output digital data having the number of bits determined by the bit number determination unit.

The principle of the fifth digital camera according to the present invention is as follows.
The A / D converter converts the gradation value indicated by the output signal of the image sensor into digital data having a predetermined maximum number of bits and digital data having at least one reduced bit number smaller than the maximum number of bits. The basic image acquisition means is a basic image composed of digital data obtained with a maximum number of bits by an A / D converter in accordance with a draft mode output output for one of the continuous frames from the image sensor prior to shooting. Get image data. The first histogram creating means creates a basic histogram indicating the frequency obtained by classifying the gradation value of each pixel constituting the basic image for each class according to the maximum number of bits based on the basic image data. The reduced image acquisition means is a digital image obtained with at least one reduced bit number by an A / D converter in accordance with a draft mode output output from the image sensor for at least one of the consecutive frames prior to shooting. At least one degenerated image data composed of data is acquired. The extended image generating means generates at least one extended image data representing the gradation value of each pixel constituting at least one degenerate image data by digital data having the maximum number of bits. The second histogram creating means creates a histogram based on at least one extended image data, and performs a class interpolation on the histogram, thereby calculating the frequency of the gradation value in each class for the digital data having the maximum number of bits. At least one reproduction histogram is generated. The evaluation unit compares the basic histogram with at least one reproduction histogram, and evaluates the magnitude of the influence that the conversion to each of the at least one degenerated image has on the image characteristics. The bit number determining means determines the bit number of the image data corresponding to the scene to be photographed based on the evaluation result by the evaluating means. The conversion control unit instructs the A / D converter to output digital data having the number of bits determined by the bit number determination unit.

According to the digital camera of the present invention, according to the characteristics of the scene to be photographed, RAW data that expresses the characteristics of the image corresponding to this scene without excess or deficiency, and is represented by digital data having an appropriate number of bits. Since the image data representing the value is generated, it is possible to effectively use the limited storage capacity of the storage medium while utilizing the characteristics of the RAW data.
In addition, regarding the image data corresponding to the shooting scene that can obtain a sufficient image quality by representing the gradation value with the digital data having the number of bits suitable for the subsequent image processing, the image having the above-described number of bits in the subsequent RAW data stage. By generating the data, it is possible to reduce the processing load on the image processing means at the subsequent stage.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(First embodiment)
FIG. 1 shows a first embodiment of a digital camera according to the present invention.
The light imaged on the image sensor 22 by the imaging optical system 21 at the time of taking an image is converted into an electric signal corresponding to the intensity by the image sensor 22, and further analog / digital (A / D) conversion. It is converted into digital data by the device 23 and held in the memory 24.

  The memory 24 shown in FIG. 1 is connected to the image processing unit 25 and the recording processing unit 26 via a bus. In a normal case, the image data stored in the memory 24 as described above is subjected to appropriate image processing including compression processing by the image correction processing unit 35 and the image compression processing unit 36 provided in the image processing unit 25. The compressed image data obtained as a result of this image processing is transferred to the recording processing unit 26 via the bus and recorded on the storage medium 27.

  In the image processing unit 25 shown in FIG. 1, the conversion control unit 31 is, for example, a RAW recording instruction that instructs the user to record raw RAW data by operating an operation panel (not shown). In accordance with the input, the size of the image data obtained by the A / D converter 23 is determined by using the functions of the shift processing unit 32, the histogram creation unit 33, and the evaluation processing unit 34 as described later. Is converted to a size suitable for the recording processing unit 26 and used for processing by the recording processing unit 26.

  The shift processing unit 32 shown in FIG. 1 performs shift processing on digital data indicating the gradation value of each pixel constituting the designated image data in accordance with an instruction from the conversion control unit 31, and performs conversion control on the shift processing result. Return to section 31. Further, the histogram creation unit 33 shown in FIG. 1 creates a histogram related to the gradation value of each pixel constituting the designated image data in accordance with an instruction from the conversion control unit 31. The histogram created by the histogram creation unit 33 is subjected to a contrast evaluation process related to image quality by an evaluation processing unit 34 described later, and an appropriate size conversion process is performed by the conversion control unit 31 based on the evaluation result.

Hereinafter, a process for recording RAW data having a data size suitable for the feature of the image by cooperation of these units will be described in detail.
FIG. 2 is a flowchart showing an appropriate size conversion operation.
At the time of shooting, digital data generated by the A / D converter 23 according to the output signal of the image sensor 22 shown in FIG. 1 is held in the memory 24 as basic image data (step 301 in FIG. 2). . In this basic image data, the gradation value relating to the color component (for example, R, G, B component) corresponding to each pixel is obtained by converting the quantization result by the A / D converter 23 into a predetermined number of bits (for example, 14 bits). ) Is represented by digital data.

  The conversion control unit 31 shown in FIG. 1 passes the basic image data held in the memory 24 as described above to the histogram generation unit 33, and generates histograms for all gradation values constituting the basic image data. In response to this, the histogram creation unit 33 creates a histogram as shown in FIG. 3A (step 302), and passes this histogram to the evaluation processing unit 34 shown in FIG.

Next, the conversion control unit 31 shown in FIG. 1 sends the above-described basic image data to the shift processing unit 32 and instructs, for example, a 2-bit right shift, and the shift processing unit 32 shifts accordingly. The image data whose number of bits has been reduced by the processing is stored in the memory 24 separately from the basic image data described above as reduced image data (step 303 in FIG. 2).
Next, the conversion control unit 31 shown in FIG. 1 passes the reduced image data generated in step 303 of FIG. 2 to the shift processing unit 32 again, and this time, by instructing a left shift of 2 bits, Restored image data in which the number of bits of each digital data constituting the above-described reduced image data is enlarged is generated by the shift processing by the shift processing unit 32 (step 304 in FIG. 2). The restored image data generated in this way is passed to the histogram creating unit 33 by the conversion control unit 31 shown in FIG. 1, and in response to this, the histogram creating unit 33 creates a histogram relating to the restored image data. (Step 305 in FIG. 2) is provided to the processing of the evaluation processing unit 34 shown in FIG.

  At this time, the histogram creation unit 33 performs an appropriate interpolation process on the histogram created directly from the above-described restored image data, and reduces the number of bits (for example, 12 bits) when the reduced image data is created. By distributing the frequencies aggregated in the corresponding classes to a plurality of classes corresponding to the classes, it is possible to attempt to reproduce a histogram corresponding to the histogram corresponding to the basic image data.

The evaluation processing unit 34 compares the histogram corresponding to the basic image data obtained in step 302 described above with the histogram corresponding to the restored image data obtained in step 305, thereby reducing the degenerated image data from the basic image data. It is evaluated whether or not there is a change in the image quality of the image represented by each conversion (step 306).
Here, a method for evaluating the change in image quality based on the contrast of the histogram will be described in detail.

  For example, the fine structure (see FIG. 3B) appearing in the distribution waveform of the portion surrounded by the dotted line in the histogram corresponding to the basic image data shown in FIG. 3A has the number of bits reduced as described above. In the process of creating the histogram corresponding to the restored image data created through the degenerated image, the frequencies are evenly distributed to the surrounding classes, so that the histogram created in step 305 may not be reproduced ( (See FIGS. 3C and 3D).

  If there are many fine structures of the distribution waveform that cannot be reproduced in the histogram corresponding to such restored image data, the characteristics of the photographed image are sufficient for a reduced image that represents a gradation value with digital data of a reduced number of bits. May not be reproduced. On the other hand, if the influence of the fine structure that cannot be reproduced is negligible, the characteristics of the photographed image are sufficiently reproduced even by the degenerate image data.

  In order to make such a determination, as shown in FIG. 4, the evaluation processing unit 34 shown in FIG. 1 first calculates the frequency of each class of the histogram corresponding to the basic image data in the histogram corresponding to the restored image data. Compared with the frequency of the corresponding class (step 311), if the difference d is larger than the threshold value Dth appropriately determined in advance (affirmative determination in step 312), the effect of degenerating the image data to the corresponding class is affected. The number of influence classes n indicating the number of affected classes is incremented (step 313).

Thereafter, the evaluation processing unit 34 determines whether or not the above-described frequency comparison has been performed for all classes (step 314). If there is an unprocessed class (negative determination in step 314), the process returns to step 311. Compare the next class.
On the other hand, when the processes related to all classes are completed (Yes in step 314), the evaluation processing unit 34 compares the influence class number n with a predetermined threshold value Nth, and the influence class number n is set to the threshold value Nth. If it is greater than the value (Yes in step 315), the determination result that the image quality is affected by the reduction in the number of bits is passed to the conversion control unit 31 and the process is terminated (step 316).

On the contrary, when the influence class number n is smaller than the threshold value Nth (negative determination in step 315), the evaluation processing unit 34 sends a determination result that the influence on the image quality due to the reduction of the bit number is small to the conversion control unit 31. Then, the process ends (step 317).
It is also possible to determine whether or not the influence on the image quality can be ignored based on the result of comparing the sum S of the differences d exceeding the threshold Dth relating to the above-described frequency difference with a threshold Sth determined appropriately in advance. is there. It is also possible to determine the threshold value Dth regarding the frequency difference of each class in consideration of the frequency value of each class. In addition, the threshold value Dth related to the frequency difference of each class, the threshold value Nth related to the influence class n, and the threshold value Sth related to the above-described sum S are, for example, as described above for image data obtained by photographing various subjects. It is possible to make a decision based on the result of an experiment in which a reduced image data is generated and an image represented by the reduced image data and an image corresponding to the basic image data are visually compared.

  As described above, when the evaluation processing unit 34 determines that the image quality is affected by reducing the number of bits of the digital data representing the gradation value (affirmative determination in step 307 in FIG. 2), 1 notifies the recording processing unit 26 of the image data stored as basic image data in the memory 24 as image data to be recorded in the storage medium 27, thereby recording the image data. (Step 308 in FIG. 2).

  On the other hand, in the case of a negative determination in step 307, the conversion control unit 31 shown in FIG. 1 determines that the image quality equivalent to the basic image data can be expected from the degenerated image data, and the basic image data held in the memory 24 is obtained. The image data is replaced with the reduced image data to obtain basic image data (step 309 in FIG. 2). Thereafter, the conversion control unit 31 determines that the number of bits of the digital data representing the gradation values constituting the basic image data is the minimum number of bits (for example, 8 bits) determined based on the number of bits of the image data suitable for the compression process, for example. ) (Step 310), and in the case of a negative determination, the process returns to step 302 to start the process for the degenerated image data that has become the basic image data as described above.

  By repeating Steps 302 to 307 and Steps 309 and 310 as described above, the number of bits of digital data representing gradation values is reduced within a range that does not affect the image quality, and a photographed image is obtained. In step 308, the image data in which the gradation value is represented by digital data of the number of bits that can reproduce the above characteristics without excess or deficiency can be used.

  In this way, raw image data having an appropriate data size is subjected to recording processing by limiting the number of bits of digital data representing gradation values in RAW data according to the characteristics of the captured image. Can do. This makes it possible to increase the number of images that can be recorded on the storage medium 27 while utilizing the characteristics of RAW data recording, so that the finite storage capacity of the storage medium 27 can be used effectively.

  2, when the number of bits of the digital data representing the gradation value in the basic image data is equal to the minimum number of bits described above, the conversion control unit 31 shown in FIG. And the basic image data composed of the digital data with the minimum number of bits obtained by replacing with the degenerated image data in step 309 is subjected to the recording process, and the process is terminated. It is also possible to provide.

  Further, as described above, instead of reducing the number of bits step by step from the image data having the maximum number of bits obtained directly from the A / D converter 23, the reduced image data corresponding to the reduced number of bits in a plurality of steps is parallelized. It is also possible to determine the limit at which degeneration is possible by comparing the histogram corresponding to the restored image data corresponding to these with the histogram corresponding to the basic image data having the maximum number of bits.

Furthermore, even when RAW data recording is not instructed, for example, the above-described reduced image data obtained by reducing the digital data representing the gradation value to the number of bits suitable for the compression processing unit 36 (for example, 8 bits) is described above. In this way, it is checked whether or not there is a change in image quality from the basic image. If it is determined that there is no change, the above-described reduced image data is used as the image correction processing unit 35 and the image compression processing unit 36 instead of the basic image data. By passing to, it is possible to reduce the processing load of each of these units.
(Second Embodiment)
FIG. 5 shows a second embodiment of a digital camera according to the present invention. FIG. 6 is a flowchart showing an appropriate size conversion operation.

5 that are the same as those shown in FIG. 1 are denoted by the same reference numerals as those shown in FIG. 1 and description thereof is omitted.
The image sensor 22 and the A / D converter 30 shown in FIG. 5 generate thinned image (draft image) data of 30 to 60 frames per second, pass it to the display control unit 28 via the memory 24, and the liquid crystal display 29 By using the display process, a through image function is provided that provides the user with the state of the subject captured by the image sensor 22 in real time.

The conversion control unit 41 shown in FIG. 5 acquires the draft image data written in the memory 24 for the above-described through image function as basic image data (see step 321 in FIG. 6).
Next, the conversion control unit 41 shown in FIG. 5 searches the limit reduction bit number that does not deteriorate the image quality as described above based on the basic image data (steps 302 to 307 and step 309 in FIG. 6). 310), the number of bits of digital data to be obtained by quantizing the output signal of the image sensor 22 at the time of shooting is determined based on the result obtained by this search, and the setting for the A / D converter 30 is performed. (Step 322).

By controlling the digitization operation in the A / D converter 30 in this way, when shooting is performed in response to pressing of the release button, an image whose gradation value is represented by digital data having an appropriate number of bits. Data can be acquired (step 323) and used for the processing of the recording processing unit 26.
As described above, prior to shooting, based on the draft image for the through image function, the influence on the image quality by reducing the number of bits of the digital data representing the gradation value is evaluated, and A / D conversion is performed. By controlling the digitization operation by the device 30, it is possible to quickly provide image data of an appropriate size corresponding to the captured image to the processing of the recording processing unit 26.

  Further, prior to step 323 shown in FIG. 6, a series of processing following step 321 is periodically repeated, for example, so that a scene change captured by the digital camera is set to the A / D converter 30. By reflecting, it is possible to digitize the output signal of the image sensor 22 with the number of bits suitable for the shot scene and obtain image data that can reproduce the features of the image corresponding to the shot scene without excess or deficiency. It is.

In addition, since the size of the basic image data to be evaluated is draft image data, and the data size is very small compared to the image data obtained at the time of shooting, creation of a histogram, degenerated image data, and restored image data It can be expected that the processing time required to create the file will be shortened.
(Third embodiment)
FIG. 7 shows a third embodiment of a digital camera according to the present invention. FIG. 8 is a flowchart showing an appropriate size conversion operation.

7 that are the same as those shown in FIG. 5 are denoted by the same reference numerals as those shown in FIG. 5 and description thereof is omitted.
The conversion control unit 42 shown in FIG. 7 acquires the draft image data written in the memory 24 for the above-described through image function as basic image data (see step 321 in FIG. 8), and the histogram shown in FIG. After creating a histogram for this basic image data by using the function of the creation unit 33, the A / D converter 30 has an appropriate reduced bit number (for example, a bit number smaller by 2 bits than the bit number corresponding to the basic image data). ) Is set (step 324).

Then, the draft image data generated for the through image function by the A / D converter 30 in which the reduced bit number is set is acquired as reduced image data (step 325), and the shift is performed based on the reduced image data. The restored image data is generated using the function of the processing unit 32 (step 304).
In this way, by controlling the digitization operation for the through image function in the A / D converter 30 for each frame, the basic image data and the degenerated image data are directly output as the output of the A / D converter 30. Obtainable.

As described above, in the digital camera according to the present invention, it is possible to determine the conditions related to quantization of gradation values necessary to make it possible to reproduce the characteristics of a captured image without excess and deficiency, and to perform digital processing with an appropriate number of bits. Image data in which gradation values are represented by data can be used for recording processing.
In this way, when recording raw image data, the number of bits of digital data representing gradation values is limited according to the characteristics of the image, and the size of the image data to be recorded is controlled appropriately. Thus, it is possible to effectively use the limited capacity of the storage medium while enjoying the advantages of RAW data recording.

  Considering that the number of bits of A / D converters provided in digital cameras is increasing year by year as digital cameras become more sophisticated, the size of recorded image data can be controlled appropriately in RAW data recording. It is a very useful feature.

It is a figure which shows 1st Embodiment of the digital camera concerning this invention. It is a flowchart showing proper size conversion operation. It is a figure explaining the image quality variation evaluation based on a histogram. It is a flowchart showing the operation | movement which evaluates the change of an image quality. It is a figure which shows 2nd Embodiment of the digital camera concerning this invention. It is a flowchart showing proper size conversion operation. It is a figure which shows 3rd Embodiment of the digital camera concerning this invention. It is a flowchart showing proper size conversion operation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 21 ... Shooting optical system, 22 ... Image pick-up element, 23, 30 ... Analog / digital (A / D) converter, 24 ... Memory, 25 ... Image processing part, 26 ... Recording processing part, 27 ... Storage medium, 28 ... Display Control unit 29 ... Liquid crystal display unit 31, 41, 42 ... Conversion control unit, 32 ... Shift processing unit, 33 ... Histogram creation unit, 34 ... Evaluation processing unit, 35 ... Image correction processing unit, 36 ... Image compression processing unit .

Claims (5)

An A / D converter that converts the gradation value indicated by the output signal of the image sensor into digital data having a predetermined maximum number of bits;
A memory for holding basic image data composed of digital data obtained by the A / D converter;
First histogram creating means for creating a basic histogram indicating the frequency obtained by classifying the gradation value of each pixel constituting the basic image for each class according to the maximum number of bits based on the basic image data; ,
Reduced image generation means for generating reduced image data representing a gradation value of each pixel by digital data having a reduced bit number smaller than the maximum bit number based on the basic image;
Extended image generation means for generating extended image data representing the gradation value of each pixel constituting the reduced image data by the digital data of the maximum number of bits;
A histogram is generated based on the extended image data, and a second histogram is generated by performing class interpolation on the histogram, thereby generating a reproduction histogram indicating the frequency of gradation values in each class regarding the digital data having the maximum number of bits. Creating means;
An evaluation means for comparing the basic histogram and the reproduction histogram and evaluating the magnitude of the influence of the conversion to the degenerate image on the image characteristics;
A digital camera, comprising: a recording control unit that uses the reduced image data for subsequent image recording processing for an image for which an evaluation result indicating that the influence is small is obtained by the evaluation unit. An A / D converter that converts the gradation value indicated by the output signal of the image sensor into digital data having a predetermined maximum number of bits;
A memory for holding basic image data composed of digital data obtained by the A / D converter;
First histogram creating means for creating a basic histogram indicating the frequency obtained by classifying the gradation value of each pixel constituting the basic image for each class according to the maximum number of bits based on the basic image data; ,
Reduced image generation means for generating reduced image data representing a gradation value of each pixel by digital data having a reduced bit number smaller than the maximum bit number based on the basic image;
Extended image generation means for generating extended image data representing the gradation value of each pixel constituting the reduced image data by the digital data of the maximum number of bits;
A histogram is generated based on the extended image data, and a second histogram is generated by performing class interpolation on the histogram, thereby generating a reproduction histogram indicating the frequency of gradation values in each class regarding the digital data having the maximum number of bits. Creating means;
An evaluation means for comparing the basic histogram and the reproduction histogram and evaluating the magnitude of the influence of the conversion to the degenerate image on the image characteristics;
The basic image from which an evaluation result indicating that the influence is small is obtained by the evaluation unit is replaced with the reduced image, and the first histogram generation unit, the reduced image generation unit, the extended image generation unit, and the new basic image. Repetitive control means for starting processing by the second histogram creating means and the evaluation means;
A digital camera comprising: a recording control unit that provides a basic image for which an evaluation result indicating that the evaluation unit has a great influence is obtained for subsequent image recording processing. An A / D converter that converts the gradation value indicated by the output signal of the image sensor into digital data having a predetermined maximum number of bits;
A memory for holding basic image data composed of digital data obtained by the A / D converter;
First histogram creating means for creating a basic histogram indicating the frequency obtained by classifying the gradation value of each pixel constituting the basic image for each class according to the maximum number of bits based on the basic image data; ,
Based on the basic image, reduced image generation means for generating reduced image data representing the gradation value of each pixel by digital data having a reduced number of bits suitable for subsequent image processing including compression processing;
Extended image generation means for generating extended image data representing the gradation value of each pixel constituting the reduced image data by the digital data of the maximum number of bits;
A histogram is generated based on the extended image data, and a second histogram is generated by performing class interpolation on the histogram, thereby generating a reproduction histogram indicating the frequency of gradation values in each class regarding the digital data having the maximum number of bits. Creating means;
An evaluation means for comparing the basic histogram and the reproduction histogram and evaluating the magnitude of the influence of the conversion to the degenerate image on the image characteristics;
A digital camera comprising: compression control means for subjecting the reduced image data to subsequent image processing for an image for which an evaluation result indicating that the influence is small is obtained by the evaluation means. An A / D converter that converts the gradation value indicated by the output signal of the image sensor into digital data having a predetermined maximum number of bits;
Prior to shooting, basic image acquisition means for acquiring basic image data composed of digital data obtained by the A / D converter according to a draft mode output periodically output from the image sensor;
First histogram creating means for creating a basic histogram indicating the frequency obtained by classifying the gradation value of each pixel constituting the basic image for each class according to the maximum number of bits based on the basic image data; ,
Reduced image generation means for generating reduced image data representing a gradation value of each pixel by digital data having a reduced bit number smaller than the maximum bit number based on the basic image;
Extended image generation means for generating extended image data representing the gradation value of each pixel constituting the reduced image data by the digital data of the maximum number of bits;
A histogram is generated based on the extended image data, and a second histogram is generated by performing class interpolation on the histogram, thereby generating a reproduction histogram indicating the frequency of gradation values in each class regarding the digital data having the maximum number of bits. Creating means;
An evaluation means for comparing the basic histogram and the reproduction histogram and evaluating the magnitude of the influence of the conversion to the degenerate image on the image characteristics;
Based on the evaluation result by the evaluation means, the bit number determination means for determining the number of bits of image data corresponding to the scene to be photographed;
A digital camera comprising: conversion control means for instructing the A / D converter to output digital data having the number of bits determined by the bit number determination means. An A / D converter that converts the gradation value indicated by the output signal of the image sensor into digital data having a predetermined maximum number of bits and at least one reduced bit number smaller than the maximum number of bits;
Prior to shooting, basic image data composed of digital data obtained with the maximum number of bits by the A / D converter in accordance with a draft mode output output for one of the continuous frames from the image sensor. Basic image acquisition means for acquiring;
First histogram creating means for creating a basic histogram indicating the frequency obtained by classifying the gradation value of each pixel constituting the basic image for each class according to the maximum number of bits based on the basic image data; ,
Prior to shooting, from the digital data obtained with the at least one reduced bit number by the A / D converter in accordance with the draft mode output output from the imaging device for at least one of the consecutive frames. Reduced image acquisition means for acquiring configured at least one reduced image data;
Extended image generating means for generating at least one extended image data representing the gradation value of each pixel constituting the at least one degenerated image data by the digital data of the maximum number of bits;
A histogram is created based on each of the at least one extended image data, and a class interpolation is performed on the histogram, whereby at least one reproduction indicating the frequency of the gradation value in each class regarding the digital data having the maximum number of bits. A second histogram generating means for generating a histogram;
An evaluation means for comparing the basic histogram and the at least one reproduction histogram to evaluate the magnitude of the effect of the conversion to each of the at least one degenerated image on the image characteristics;
Based on the evaluation result by the evaluation means, the bit number determination means for determining the number of bits of image data corresponding to the scene to be photographed;
A digital camera comprising: conversion control means for instructing the A / D converter to output digital data having the number of bits determined by the bit number determination means.

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