JP2007142683A - Digital still camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To allow fixed-length compression at high speed and high precision. <P>SOLUTION: The digital still camera comprises a fixed-length compression means which generates a compressed data within a specified range including a target size for recording process, by adjusting a compression parameter for compressing an input image data; an initial value calculating means for calculating an initial value of compression parameter about the image data of a current frame, based on a previous compression parameter applied to the image data of a previous frame, a compression data size, and a target size, according to a mode setting instruction indicating a consecutive photographing mode; and a consecutive compression means for generating a compressed data within a specified range including a target size, by applying the initial value of the compression parameter acquired by the initial value calculating means. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a digital still camera that records after compressing image data representing a photographed image.

In a digital still camera, a target file size for recording image data is often determined in advance in accordance with image quality settings (for example, FINE: high definition, NORMAL: standard, BASIC: basic) by a user.
In such a digital still camera, the image data obtained by shooting is repeatedly subjected to test compression while changing the compression parameter to search for the optimum compression parameter and recognize the target file size corresponding to the image quality setting. The image data is compressed so as to be within the allowable range.

  This is because, in the JPEG method widely used for still image compression processing in digital still cameras, the size of compressed data obtained after compression varies greatly depending on the characteristics of the captured scene, so image data obtained by capturing various scenes. This is because it is necessary to apply compression to each image data by applying an appropriate quantization parameter in order to keep the size of the compressed data obtained for the above in a predetermined range. For example, for image data obtained by shooting scenes rich in changes with many high-frequency components, the compression rate is increased to reduce the size of the compressed data, while for image data corresponding to scenes with little change, The compression rate is kept small so that the size of the compressed data does not become too small.

Such adjustment of the compression rate is performed by adjusting the quantization parameter used when encoding the image data according to the JPEG method by the scale factor SF, thereby realizing a fixed length of the compressed data. Has been.
In the conventional general fixed length technology, pre-compression is performed a few times while changing the scale factor, and the optimal scale factor is estimated based on the change in the size of the compressed data obtained at this time. The final compressed data is obtained by applying the optimum value of the scale factor.

In addition, a method for obtaining an optimum value of a scale factor based on a single preliminary compression result using a model related to a change in the size of compressed data corresponding to a change in the scale factor has been proposed (Patent Document). 1).
In addition, for a plurality of image data obtained by continuous shooting, using the fact that these image data have similar characteristics, the scale factor obtained for the first frame is also applied to the second and subsequent frames. Thus, there has also been proposed a method for realizing a certain fixed length for compressed data while realizing high-speed processing required for continuous shooting (see Patent Documents 2, 3, and 4).

In this way, by compressing the size of the compressed data to a substantially fixed length, at the stage of recording a compressed image on a medium such as a flash card, the number of images expected to correspond to the image quality is the number of images recorded on the medium. Guaranteed.
JP 2004-56680 A JP 10-117352 A JP-A-3-267877 JP-A-4-170879

As the number of pixels of digital still cameras increases, the user base of digital still cameras has expanded to include semi-professionals and professionals, and at the same time, the quality of recorded images is improved and the processing of captured images is required. There is an increasing demand for shortening the time.
In particular, in order to support fixed-length compression of continuously captured image data, it is apparent that there is a limit to the processing speed in the method of optimizing the scale factor from a few preliminary compressions. This is because if the clock frequency of the image processing LSI is increased to increase the processing speed, the power consumption is increased, the battery is exhausted and sufficient operating time cannot be secured. There is also an upper limit on the clock frequency, and there is a limit to the speedup of the compression process that can be achieved by simply operating the hardware at high speed.

Even if the technique of Patent Document 1 described above is applied, if the shooting interval at the time of continuous shooting is shortened, the fixed length is set according to the time required for performing the pre-compression on all continuously shot images. There is a possibility that the conversion process cannot catch up.
On the other hand, if the scale factor obtained for the first frame of image data is applied to the second and subsequent frames as in the techniques disclosed in Patent Documents 2 to 4, a plurality of image data obtained by continuous shooting can be processed at high speed. It is possible to perform compression processing.

  However, whether or not the compressed data obtained by this method falls within an allowable range related to the target file size depends on the degree of similarity between a plurality of images that are continuously captured. For this reason, there is a case where the fixed length of the compressed data cannot be reliably guaranteed. For example, when a subject that moves greatly in the field is photographed over a relatively long period of time, the characteristics may vary greatly between the first frame image and the last image of continuous shooting. Conceivable. In such a case, if the scale factor of the first frame is simply applied to the compression of the last image as it is, the compressed data corresponding to the first frame and the compressed data corresponding to the last frame are large in size. There will be a gap. In the worst case, compressed data corresponding to a part of a plurality of continuously shot images may not be recorded on the medium.

  An object of the present invention is to provide a digital still camera capable of compressing fixed length image data at high speed and with high accuracy.

A first digital still camera according to the present invention includes an imaging unit, a fixed length compression unit, an initial value calculation unit, and a continuous compression unit.
The principle of the first digital still camera according to the present invention is as follows.
In a digital still camera that compresses and records image data representing a digital still image captured by the imaging unit, the fixed length compression unit includes a target size by adjusting a compression parameter for compressing the input image data. Compressed data compressed within a predetermined range is generated and used for recording processing. The initial value calculating unit is configured to detect the immediately preceding compression parameter and the compressed data size applied to the image data of the immediately preceding frame in accordance with a mode setting instruction indicating a continuous shooting mode indicating that images are continuously captured by the capturing unit, and a target Based on the size, an initial value of a compression parameter for the image data of the current frame is calculated. The continuous compression means generates compressed data compressed within a predetermined range including the target size by applying the initial value of the compression parameter obtained by the initial value calculation means.

The operation of the first digital still camera configured as described above is as follows.
For example, after one frame of image data acquired by the photographing unit is compressed by the fixed-length compression unit, new image data is acquired continuously, and the continuous shooting mode is set in accordance with the mode setting instruction. When instructed, the parameter calculation means calculates a compression parameter corresponding to the newly input image data of the current frame using the compression parameter used for the compression of the first frame image data. The compression parameter is provided to the process of the continuous compression means as the initial value of the compression parameter estimation process.

  Here, in the continuous shooting mode, the image data of the current frame and the image data of the immediately preceding frame can be expected to have very similar characteristics, so the compression parameters applied to the immediately preceding frame are set to the size of the compressed data of the immediately preceding frame and By adjusting based on the target size, it is possible to determine the initial value of the compression parameter suitable for the characteristics of the image data of the current frame. As described above, by using the similarity of images of consecutive frames in the continuous shooting mode and reflecting the difference between the compressed data size in the immediately preceding frame and the target size in the initial value of the compression parameter of the current frame, Therefore, the initial value of the compression parameter can be made to follow a minute change tendency of the image feature between frames. Therefore, if the change in the characteristics of the image data is gradual, the image data is compressed by applying the initial value of the compression parameter obtained as described above, so that the image data is almost surely compressed within a predetermined range including the target size. Compressed data can be obtained. That is, in the continuous compression means, the compressed data obtained by applying the initial value of the compression parameter calculated as described above can be used as it is as the main compression result for the recording process via the compression control means.

When the continuous shooting mode is not instructed or when the continuous shooting mode is canceled, the image data acquired by the photographing unit is compressed by the fixed length compression unit and used for recording processing.
In the second digital still camera according to the present invention, the initial value calculating means is based on the immediately preceding compression parameter applied to the image data of the immediately preceding frame compressed by the fixed length compressing means, the compressed data size and the target size. Then, the initial value of the compression parameter for the image data of the current frame is calculated.

Such a second digital still camera uses the initial value calculated using the immediately preceding compression parameter adjusted so as to be optimal for the image characteristics of the immediately preceding frame by the fixed-length compression means, and uses the initial value of the immediately preceding frame. The image data of the current frame that can be expected to be similar to the image data can be compressed.
In the third digital still camera according to the present invention, the initial value calculating means is based on the immediately preceding compression parameter, the compressed data size and the target size applied to the image data of the immediately preceding frame compressed by the continuous compressing means. The initial value of the compression parameter for the image data of the current frame is calculated.

Such a third digital still camera uses the similarity of image data that can be expected when the continuous shooting mode is continued, and an appropriate compression parameter is applied to the image data of the current frame by the initial value calculation means. It can be calculated as an initial value and used for processing of the continuous compression means.
The fourth digital still camera according to the present invention is configured such that, in the first digital still camera described above, the initial value calculating means includes a size adjusting means.

The principle of the fourth digital still camera according to the present invention is as follows.
In the initial value calculating means provided in the first digital still camera described above, the size adjusting means adjusts the target size of the current frame in consideration of the difference between the compressed data obtained corresponding to the immediately preceding frame and the target size. And used for compression parameter calculation processing.
The operation of the fourth digital still camera configured as described above is as follows.

By adjusting the target size used for calculating the compression parameter of the current frame by the size adjusting means, the error between the compressed data and the target size in each frame is absorbed in the compression processing of the next frame, so that The average size of the compressed data recorded corresponding to the captured image converges to the target size with high accuracy.
A fifth digital still camera according to the present invention is the same as the first digital still camera described above, wherein the initial value calculation means includes adjustment means and multiplication means.

The principle of the fifth digital still camera according to the present invention is as follows.
In the initial value calculating means provided in the first digital still camera described above, the adjusting means corresponds to the immediately preceding frame based on the ratio between the size of the compressed data obtained corresponding to the immediately preceding frame and the target size. The parameter for calculating the compression parameter of the current frame is adjusted from the obtained compression parameter. The multiplication means obtains the scale factor of the current frame by multiplying the adjusted parameter by the scale factor applied as the compression parameter in the immediately preceding frame, and uses this scale factor for the processing of the continuous compression means.

The operation of the fifth digital still camera configured as described above is as follows.
By adjusting the parameter for calculating the compression parameter of the current frame by the adjusting means, and subjecting this parameter to the multiplication process with the scale factor of the immediately preceding frame by the multiplying means, the target size of the compressed data corresponding to the immediately preceding frame The compression parameter to be applied to the image data of the current frame can be calculated by appropriately reflecting the deviation from the size.

For example, the initial value calculation means appropriately sets the scale factor SF (new) of the current frame, the scale factor SF (old) of the immediately preceding frame, the compression size S (old) of the immediately preceding frame, and the target size Ts in advance. It can be obtained by using the expression (1) expressed using the parameter a.
SF (new) = (S (old) / Ts) ^{(−1 / a)} · SF (old) (1)
The sixth digital still camera according to the present invention is the same as the first digital still camera described above, wherein the continuous compression means includes determination means, selection means, and estimation means.

The principle of the sixth digital still camera according to the present invention is as follows.
In the above-described continuous compression unit provided in the first digital still camera, the determination unit includes a difference between the compressed data size obtained by applying the initial value of the compression parameter calculated by the initial value calculation unit and the target size. Is determined to be within the allowable range. The recompressing means determines the initial value and the compressed data size obtained by applying the initial value and the target size according to the determination result that the difference between the compressed data size and the target size exceeds the allowable range. Is used to estimate an optimal compression parameter and apply the estimated compression parameter to generate compressed data of the image data.

The operation of the sixth digital still camera configured as described above is as follows.
For example, even when the continuous shooting mode is set by the user, for example, when following the subject while panning the camera, the characteristics of the captured image data change abruptly from the middle, There may be a case where the difference between the compressed data obtained by applying the initial value of the compression parameter calculated as described above to the image data of the current frame and the target size exceeds the allowable range. In such a case, in accordance with the determination result by the determination unit, the compression parameter is estimated by using the compression data obtained by the compression process to which the compression parameter obtained by the initial value calculation unit is applied by the recompression unit as a preliminary compression result. The processing is performed, and the compression result obtained by applying the optimized compression parameter is used for the recording process. Since the optimized compression parameter obtained in this process is used for the subsequent compression parameter calculation processing, it can flexibly cope with a sudden change in an image during continuous shooting and maintain fixed length compression. be able to.

A seventh digital still camera according to the present invention is the same as the sixth digital still camera described above, except that the recompressing means includes a selecting means.
The principle of the seventh digital still camera according to the present invention is as follows.
In the recompression unit provided in the sixth digital still camera described above, the selection unit selects the initial value of the compression parameter according to the determination result that the difference between the size of the compressed data and the target size exceeds the allowable range. Based on the above, an appropriate adjustment parameter is selected, and an optimal compression parameter using the initial value of the compression parameter, the compressed data size obtained by applying the initial value, and the target size is selected as the selected adjustment parameter. It is used for the estimation process.

The operation of the seventh digital still camera configured as described above is as follows.
When the determination unit obtains a determination result that the size of the compressed data is not within the allowable range, the selection unit performs an appropriate adjustment based on the initial value of the compression parameter obtained by the initial value calculation unit. A parameter is selected and subjected to an optimal compression parameter estimation process. As a result, for example, using the knowledge about the slope parameter obtained by accumulating the relationship between the scale factor and the compressed data size for various image data, the compression parameter (in this case, the scale factor) can be calculated with higher accuracy. Can be estimated.

The eighth digital still camera according to the present invention is the same as the first digital still camera described above, comprising information collecting means and mode setting means.
The principle of the eighth digital still camera according to the present invention is as follows.
In the first digital still camera described above, the information collecting unit collects information indicating the photographing conditions related to the photographing process by the photographing unit. When the mode setting means determines that the photographing means is performing continuous photographing processing based on the information collected by the information collecting means, the mode setting means sends a mode setting instruction indicating the continuous shooting mode to the parameter calculating means and the input control. Enter the means.

The operation of the eighth digital still camera configured in this way is as follows.
The mode setting means inputs a mode setting instruction indicating the continuous shooting mode to the parameter calculation means only when the information collected by the information collecting means indicates that continuous photographing processing is being performed by the photographing means. Start the compression process suitable for continuous shooting. In addition, when the information collected by the information collecting means changes to become information indicating individual photographing processing, the mode setting means stops the input of the mode setting instruction indicating the continuous shooting mode, and the continuous shooting mode Is released. In response to this, the image data of the current frame is input to the fixed length compression means by the input control means, and the compression result by the fixed length compression means is used for the recording process.

The ninth digital still camera according to the present invention is the same as the eighth digital still camera described above, wherein the information collecting means includes interval collecting means, and the mode setting means includes interval determining means.
The principle of the ninth digital still camera according to the present invention is as follows.
In the information collecting means provided in the above-described eighth digital still camera, the interval collecting means collects time intervals related to acquisition of image data by the photographing means as information indicating photographing conditions. In the mode setting unit, the interval determining unit determines that the imaging unit is performing continuous imaging processing when the time interval is equal to or less than a predetermined threshold.

The operation of the ninth digital still camera configured in this way is as follows.
Depending on whether or not the time interval collected by the interval collecting means is equal to or less than a predetermined threshold, the interval judging means judges whether or not the photographing means is performing continuous photographing processing, and in accordance with this, the mode By operating the setting instruction, continuous compression processing and fixed-length compression processing are automatically switched.

A tenth digital still camera according to the present invention is the same as the eighth digital still camera described above, wherein the information collecting means includes sensitivity collecting means, and the mode setting means includes sensitivity determining means.
The principle of the tenth digital still camera according to the present invention is as follows.
In the information collecting means provided in the above-described eighth digital still camera, the sensitivity collecting means collects the photographing sensitivity for each piece of image data acquired by the photographing means as information indicating the photographing condition. In the mode setting means, the sensitivity determination means is configured to perform continuous shooting when the difference between the shooting sensitivity collected for the current frame by the sensitivity collection means and the shooting sensitivity corresponding to the previous frame is equal to or less than a predetermined threshold. It is determined that processing is being performed.

The operation of the tenth digital still camera configured as described above is as follows.
If there is a large difference in shooting sensitivity between the current frame and the previous frame collected by the sensitivity collecting means, the sensitivity judging means performs continuous shooting processing regardless of the length of the shooting interval. Therefore, it is automatically switched from compression processing by the parameter calculation means and continuous compression means to compression processing by the fixed length compression means, and the image data of the current frame is appropriately fixed by the fixed length compression means. Long compressed.

The digital still camera according to the present invention achieves high-speed processing required for compression processing during continuous shooting, and targets the size of compressed data regardless of changes in image characteristics that often appear during continuous shooting. The size can be converged with extremely high accuracy.
As a result, it is possible to reliably ensure that the compressed data corresponding to the number of images defined in accordance with the image quality setting is recorded on the medium. For example, the compression corresponding to the image acquired by continuous shooting is performed. It is possible to completely prevent a problem that a part of data is not recorded on the medium.

(First embodiment)
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a first embodiment of a digital still camera according to the present invention.
In the digital still camera shown in FIG. 1, an image formed on the image sensor 12 by the photographing optical system 11 is converted into an electric signal by the image sensor 12 and processed by the signal processing unit 13 and the A / D conversion unit 14. Thus, it is converted into image data representing a digital still image. The image data obtained in this way is subjected to image quality adjustment processing by the image processing unit 15 and then passed to the compression processing unit 16 via the memory 20, and the compression processing unit 16 corresponds to image quality setting. The data is compressed to a size and recorded on a storage medium such as a memory card via the recording unit 17.

  The control unit 18 illustrated in FIG. 1 controls the operation of each unit described above according to instructions input by the user via the operation panel 19. For example, the control unit 18 is provided in the operation panel 19. The information indicating the image quality (FINE, NORMAL, BASIC, etc.) set by operating the button or the like and the information related to the shooting conditions are passed to the compression processing unit 16, and the compression processing unit 16 accordingly receives the received image quality setting. The fixed length compression is performed as described below with reference to a target size determined in advance corresponding to the information.

FIG. 2 shows a detailed configuration of the compression processing unit.
In the compression processing unit 16 shown in FIG. 2, the encoding unit 21 applies the compression parameter received from the compression control unit 23 and encodes the image data stored in the memory 20 according to the JPEG method. Compress. The compression control unit 23 controls the compression parameter estimation operation by the parameter estimation unit 22 based on the comparison result between the compressed data size obtained by the encoding unit 21 and the target size, and sets an appropriate compression parameter. A search is performed to control the size of the image data to converge to the target size.

  In FIG. 2, the image quality setting information input by operating the operation panel 19 is detected by the image quality setting detection unit 31 provided in the control unit 18, and the compression control unit 23 provided in the compression processing unit 16. And the target size is determined accordingly. In the control unit 18 illustrated in FIG. 2, the interval measurement unit 32 collects, for example, information on the time when individual image data is acquired from the signal processing unit 13, and based on this, the image data acquisition interval is collected. And the measurement result is passed to the mode determination unit 24 provided in the compression processing unit 16. On the other hand, for example, the sensitivity information collection unit 33 illustrated in FIG. 2 collects information indicating shooting sensitivity regarding individual shooting from the signal processing unit 13 and passes the collected information to the mode determination unit 24 described above.

  The mode determination unit 24 illustrated in FIG. 2 is an image in which image data newly input can be applied with compression processing in a continuous shooting mode, which will be described later, based on the information regarding the imaging conditions input from the control unit 18 described above. It is determined whether it is data. Also, the compression control unit 23 shown in FIG. 2 uses a standard initial value SF1 appropriately determined in advance as an initial value used for calculating the scale factor SF based on the determination result by the mode determination unit 24, or as will be described later. Then, one of the adjusted initial value SF11 obtained by the parameter estimation unit 22 based on the scale factor of the immediately preceding frame is used for the processing of the encoding unit 21.

FIG. 3 is a flowchart showing an outline of the operation of the compression processing unit.
First, information related to shooting conditions (for example, shooting interval and shooting sensitivity) is received from the control unit 18, and based on this information, whether or not the continuous shooting mode should be applied to image data to be compressed by the mode determination unit 24. Is determined (steps 301 and 302). At this time, the mode determination unit 24 determines, for example, whether or not the shooting interval D is equal to or less than a predetermined threshold Dth as the condition determination regarding the shooting interval D, and the shooting sensitivity of the immediately preceding frame as the condition determination regarding the shooting sensitivity V. It is determined whether or not the difference between V _old and the shooting sensitivity V of the current frame is equal to or less than a predetermined threshold value _Vth , and it is determined that the continuous shooting mode should be applied when both conditions are satisfied. Accordingly, the continuous shooting mode can be applied only when high similarity can be expected between the image of the immediately preceding frame and the image of the current frame.

  For example, in the first frame shot after the digital still camera is turned on, neither the above-described shooting interval condition nor shooting sensitivity condition is satisfied, so the mode determination unit 24 does not apply the continuous shooting mode. A determination result to that effect is passed to the compression control unit 23 (No determination in step 302). In response to this, the compression control unit 23 determines that the image data of the current frame should be individually compressed, and in advance compresses each image data independently (hereinafter referred to as individual mode compression). The determined standard scale factor initial value SF1 is subjected to compression processing by the encoding unit 21 (step 303).

In the individual mode compression, the encoding unit 21 performs preliminary compression using the above-described initial value SF1 (step 304), and then the compression control unit 23 performs the compression data size S1 obtained by this preliminary compression. Is determined to be within the allowable range set for the target size Ts corresponding to the image quality setting, it is determined whether or not the fixed length compression has been completed (step 305). At this time, the compression control unit 23 compares the lower limit value S _min and the upper limit value S _max of the size of the compressed data set in advance based on the target size Ts with the size S ₁ of the pre-compressed data. When it is determined that the upper limit value _Smax is exceeded (or less than the lower limit value), it is determined that the fixed length compression has not been completed (No determination in step 305).

In this case, in response to an instruction from the compression control unit 23, the parameter estimation unit 22 sets the initial value of the scale factor applied to the first preliminary compression (SF1 in the case of the individual mode) and the first preliminary compression result. Using the size S ₁ of the obtained compressed data, the target size Ts, and the coefficient a _i adjusted for each estimation number i based on the statistical relationship between the scale factor and the size of the compressed data, The i-th scale factor SF _i expressed as 2) is estimated (step 306).

SF _i = (S ₁ / Ts) ^{(−1 / ai)} · SF 1 (2)
For details regarding the estimation of the scale factor SF, refer to Japanese Patent Application Laid-Open No. 2003-179926.
Next, as long as the number of preliminary compressions (or the estimated number of scale factors) does not exceed the specified number N, the compression control unit 23 returns to step 304 as a negative determination in step 307 and is estimated as described above. The encoding unit 21 is caused to execute compression processing to which the new scale factor SF _i is applied. At this time, the compression control unit 23 limits the estimated value of the new scale factor SF _i using the upper limit value SF _max and the lower limit value SF _min that are set in advance for the value of the scale factor. The scale factor SF _i is applied to the encoding unit 21.

  If the fixed-length compression has not yet been completed even though the number of preliminary compressions exceeds the above-mentioned number of times, the compression control unit 23 determines that a hardware failure has occurred and performs appropriate error processing. To finish the process. In addition, after the predetermined number of trials (for example, the fourth time), instead of performing the estimation based on the above-described equation (2), the cutoff scale factor SF4, the coefficient c (c> 1), and the equation (3) ) May be used to estimate the scale factor.

SF _i = SF4 · c ^i-1 (3)
When the pre-compression and the estimation of the scale factor described above are repeated, and the compressed data whose size S is not less than the lower limit value S _{min and not} more than the upper limit value S _max is obtained, the compression control unit 23 It is determined that the fixed length compression has been completed (Yes determination at step 305). In response to this, the compressed data finally obtained by the encoding unit 21 is output to the recording unit 17 (step 308), and the last applied scale factor value and the size of the compressed data are the same as the previous frame. The scale factor SF (old) and the size S (old) are stored in the compression control unit 23 (step 309).

In the case where the size S of the compressed data obtained by the encoding unit 21 is less than the lower limit value S _min and the scale factor value applied to the pre-compression is the above-described lower limit value SF _min , It is determined that the current frame image has a characteristic that the code amount is extremely small (for example, there are few components with high spatial frequency like an image showing the sky), and it is determined that the fixed-length compression processing has been completed. . In this case as well, the compressed data is output and the scale factor is stored (steps 308 and 309). In addition, when compression is performed by applying the truncation scale factor SF4 described above, the compression control unit 23 determines that the fixed length compression is completed when the size S of the compressed data is less than the upper limit value _Smax. Only when the size S exceeds the upper limit value _Smax , the estimation of the scale factor using the above-described equation (3) may be applied.

Thereafter, unless an instruction to end shooting is given through the control unit 18, the compression control unit 23 returns to step 301 as a negative determination in step 310, receives information on the shooting conditions corresponding to the new frame, and The compression process for the frame is started.
Based on the information received corresponding to the new frame, when the mode determination unit 24 obtains a determination result indicating that the continuous shooting mode should be applied (positive determination in step 302), the compression control In response to an instruction from the unit 23, the parameter estimation unit 22 performs an estimation process of the initial value of the scale factor (step 311).

  At this time, the parameter estimation unit 22 stores the scale factor SF (old) and size S (old) stored in step 309 of the compression process of the immediately preceding frame, the target size Ts, the coefficient a determined appropriately, and the above-described value. Using equation (1), the scale factor SF (new) of the current frame is estimated, and this value is returned to the compression control unit 23 as the initial value SF11 of the scale factor. Here, the value of the coefficient a described above is based on the relationship obtained for the scale factor and the size of the compressed data by statistically analyzing information accumulated in advance for images having various characteristics, for example, It is determined by calculating an average value of parameters indicating the relationship obtained for each image, and is used for estimation processing of the initial value SF11 of the scale factor.

  Thus, the estimated initial value SF11 of the scale factor reflects the characteristics of the image corresponding to the previous frame, and is adjusted based on the ratio between the compressed data of the previous frame and the target size. ing. Therefore, when the image of the current frame is similar to the image of the immediately preceding frame, the scale factor SF11 estimated as described above is applied to the compression processing in step 304, so that the size is almost certainly allowed. Compressed data that falls within the range can be obtained. Therefore, in this case, the compression result obtained by applying the scale factor SF11 estimated as described above can be used as the main compression result, and the compressed data obtained as the compression result is output to the recording unit. (Step 308) The scale factor SF11 and the size S of the compressed data are stored for the compression process in the next frame (Step 309).

When the continuous shooting mode is to be applied as described above, the similarity between the current frame image and the previous frame image is often high. Therefore, most of the image data to be compressed while the continuous shooting mode is applied is compressed to a fixed length by the compression process using the scale factor estimated as described above.
Here, as described above, instead of using the scale factor of the previous frame as it is, by adjusting based on the ratio between the compressed data of the previous frame and the target size, the scale factor of the current frame is obtained. An error between the size of the compressed data obtained in the previous compression process and the target size can be corrected in the compression process for the current frame. That is, when the size of the compressed data obtained in the previous frame is smaller than the target size Ts, the scale factor of the current frame is adjusted to be slightly smaller than that of the previous frame. If it is larger than the size Ts, the scale factor of the current frame is adjusted to be slightly larger than the previous frame. By performing such correction, when the characteristics of a plurality of continuously shot images are changing little by little, the scale factor value can follow the change. As a result, the size of the compressed data obtained by the compression processing for the current frame can be made closer to the target size Ts, and high-speed and high-precision fixed-length compression can be realized.

  Furthermore, the target value Ts ′ for the size of the compressed data relating to the current frame can be adjusted according to the target size Ts corresponding to the image quality setting and the compressed data size S (old) of the previous frame. For example, if the scale factor is estimated by substituting the target value Ts ′ represented by the equation (4) into the equation (1) instead of the target size Ts corresponding to the image quality setting, the compressed data of the previous frame The size of the compressed data obtained in correspondence with the large number of image data that is the target of compression processing during the period when the continuous shooting mode is applied. Can be converged to the target size with high accuracy.

Ts ′ = 2Ts−S (old) (4)
On the other hand, even when the continuous shooting mode is applied, the characteristics of the image of the previous frame may be greatly different from the characteristics of the image of the current frame. In such a case, as described above. In the estimated scale factor SF11, there is a possibility that a non-negligible error may occur between the compressed data size S and the target size Ts.

  In such a case, step 304 to step 307 are repeated in the same manner as in the individual mode compression processing described above, using the compressed data obtained by the compression processing using the scale factor SF11 estimated in step 303 as a preliminary compression result. The optimum value of the scale factor SF is estimated, and the compressed data obtained by applying the estimated scale factor is output to the recording unit 17 as the main compression result. Fixed length compression can be realized while flexibly responding to large changes. At this time, the parameter estimation unit 22 uses the equation (the following equation (5)) in which the initial value SF1 of the scale factor in equation (2) is replaced with the initial value SF11 of the scale factor estimated in step 311 described above. The i-th estimation parameter estimation process is performed.

SF _i = (S ₁ / Ts) ^{(−1 / ai)} · SF11 (5)
Of course, by repeating the preliminary compression in this way, the time required for the compression processing for the corresponding frame becomes longer than the case where the scale factor estimated in step 311 can be used as it is. However, since the frames that require such processing are only a part of many images that are taken during the period when the continuous shooting mode is applied, the average processing time as a whole is sufficiently high. It is possible to fit within the shooting interval for continuous shooting. Therefore, the advantage of having fixed length compression guaranteed by flexibly responding to changes in image characteristics that may occur during continuous shooting is greater.
(Second Embodiment)
FIG. 4 shows another configuration example of the compression processing unit according to the present invention.

In the compression processing unit 16 shown in FIG. 4, the coefficient table 25 includes coefficients used for estimating the scale factor in the continuous shooting mode in addition to the standard coefficient a _i series used for estimating the scale factor in the individual mode. The series of a _i is stored for each of the plurality of sections set for the value obtained as the initial value of the scale factor by the estimation process in step 311 described above.

  From the data accumulated for image data having various characteristics, it is known that there is a relationship as shown in FIG. 5A between the value of the scale factor and the size of the compressed data. As can be seen from FIG. 5A, as the scale factor value increases, the size of the compressed data decreases monotonously, but there are several graphs showing the relationship between the compressed data size and the scale factor. Has an inflection point.

Therefore, for each section obtained by dividing the scale factor at the inflection point described above, an appropriate scale factor can be obtained with higher accuracy by switching the value of the coefficient a indicating the slope of the change in the compressed data size with respect to the change in the scale factor. Can be estimated.
For example, as shown in FIG. 5A, when three inflection points appear in the graph indicating the relationship between the size of the compressed data and the scale factor, the value of the scale factor is changed at these inflection points. For the four sections obtained by partitioning, the slopes in the respective sections of the graph relating to a plurality of images having representative characteristics are stored in the coefficient table 25 as a series of coefficients a _i . That is, in the coefficient table 25, as shown in FIG. 5B, a series of coefficients a corresponding to each of the sections 1 to 4 is stored together with a standard series including the coefficients a _S2 and a _S3. . In FIG. 5B, the coefficients used for estimating the i-th estimated value SFi when the initial value SF11 of the scale factor belongs to the section j are shown with suffixes j and i.

Next, a method for estimating an optimum scale factor using such a coefficient table 25 will be described.
First, the parameter estimation unit 22 determines whether or not the continuous shooting mode is applied (step 312). If the determination is negative, the parameter estimation unit 22 corresponds to the estimated number of times i corresponding to the standard sequence shown in FIG. Then, the coefficient a _Si stored in the coefficient table 25 is selectively read out (step 313), the i-th scale factor is estimated using this coefficient a _Si and the above-described equation (2) (step 314), and compression is performed. The data is supplied to the processing of the encoding unit 21 via the control unit 23.

On the other hand, in the case of an affirmative determination in step 312, the parameter estimation unit 22 corresponds to the estimation number i corresponding to the series corresponding to the section j to which the initial value SF11 of the scale factor estimated in step 311 described above belongs. 25, the coefficient a _ji stored in 25 is selectively read out (step 313), the i-th scale factor is estimated using the coefficient a _Si and the above equation (2) (step 314), and the compression control unit 23 is To the processing of the encoding unit 21. Note that the parameter estimation unit 22 first estimates the scale factor based on the preliminary compression result obtained by applying the initial value of the scale factor, and the initial value SF11 of the scale factor described above and the inflection described above. By comparing with the value of the scale factor corresponding to the point, the section j to which the initial value SF11 belongs can be determined, and this section j can be stored and used for the subsequent estimation processing.

  In this manner, in the estimation process of the scale factor in the continuous shooting mode, by appropriately using the appropriate coefficient series according to the initial value of the scale factor calculated using the scale factor of the previous frame, The estimation accuracy of the scale factor can be improved, and the size of the compressed data can be converged to the target size with higher accuracy.

  As described above, the digital still camera according to the present invention realizes high-speed operation required for continuous shooting and the like, and eliminates the convergence error of the size caused by the change of the image feature that has been overlooked in the past. In addition, it is possible to reliably compress the compressed data corresponding to a large number of continuously photographed images. Accordingly, since all of the captured images can be compressed and recorded within a predetermined range including the target size corresponding to the image quality setting, the storage capacity of the storage medium can be used without waste, and various scenes can be captured. Regardless of the nature, it is possible to reliably record the number of images obtained from the storage capacity and the target size of the storage medium on the storage medium. That is, the storage capacity of the storage medium can be utilized to the maximum.

  With such a feature, the digital still camera according to the present invention can reliably record more compressed images on a storage medium at a shorter shooting interval, so that a general user can take a picture as a hobby. Of course, it can fully meet the strict requirements of semi-professional and professional photography.

It is a figure which shows 1st Embodiment of the digital still camera concerning this invention. It is a figure which shows the detailed structure of a compression process part. It is a flowchart showing the outline of operation | movement of a compression process part. It is a figure which shows another structural example of a compression process part. It is a figure explaining parameter estimation operation. It is a flowchart showing the operation | movement which estimates the optimal value of a scale factor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Imaging optical system, 12 ... Image sensor, 13 ... Signal processing part, 14 ... A / D conversion part, 15 ... Image processing part, 16 ... Compression processing part, 17 ... Recording part, 18 ... Control part, 19 ... Operation Panel, 20 ... Memory, 21 ... Encoding unit, 22 ... Parameter estimation unit, 23 ... Compression control unit, 24 ... Mode determination unit, 25 ... Coefficient table

Claims (10)

In a digital still camera that compresses and records image data representing a digital still image photographed by a photographing means,
Fixed-length compression means for adjusting the compression parameters for compressing the input image data, generating compressed data compressed within a predetermined range including the target size, and using it for recording processing;
Based on the previous compression parameter and compression data size applied to the image data of the previous frame and the target size in response to a mode setting instruction indicating a continuous shooting mode indicating that images are continuously captured by the photographing unit. Initial value calculating means for calculating an initial value of the compression parameter for the image data of the current frame;
Continuous compression means for generating compressed data compressed within a predetermined range including the target size by applying an initial value of a compression parameter obtained by the initial value calculating means, camera. The digital still camera according to claim 1.
The initial value calculating means compresses the image data of the current frame based on the immediately preceding compression parameter and the compressed data size applied to the image data of the immediately preceding frame compressed by the fixed length compressing means and the target size. A digital still camera that calculates initial values of parameters. The digital still camera according to claim 1.
The initial value calculation means includes a compression parameter for the image data of the current frame based on the immediately preceding compression parameter applied to the image data of the immediately preceding frame compressed by the continuous compression means, the compressed data size, and the target size. A digital still camera that calculates an initial value of. The digital still camera according to claim 1.
The initial value calculating means includes
A digital adjusting system comprising a size adjusting unit for adjusting a target size of a current frame in consideration of a difference between the compressed data obtained corresponding to the immediately preceding frame and the target size, and for use in a compression parameter calculation process. Still camera. The digital still camera according to claim 1.
The initial value calculating means includes
Based on the ratio between the compressed data size obtained for the immediately preceding frame and the target size, the parameter for calculating the compression parameter for the current frame from the compression parameters obtained for the immediately preceding frame is adjusted. Adjusting means to
Multiplying means for obtaining the scale factor of the current frame by multiplying the adjusted parameter by the scale factor applied as the compression parameter in the immediately preceding frame, and providing the scale factor to the processing of the continuous compression means. Digital still camera. The digital still camera according to claim 1.
The continuous compression means further includes
Determining means for determining whether a difference between the size of the compressed data obtained by applying the initial value of the compression parameter calculated by the initial value calculating means and the target size is within an allowable range;
In accordance with a determination result that the difference between the size of the compressed data and the target size exceeds an allowable range, the initial value and the size of the compressed data obtained by applying the initial value and the target size are A digital still camera, comprising: a recompression unit that estimates an optimal compression parameter by using the compression parameter and generates compressed data of the image data by applying the estimated compression parameter. The digital still camera according to claim 6.
The recompression means includes
In accordance with a determination result that the difference between the size of the compressed data and the target size exceeds an allowable range, a selection unit that selects an appropriate adjustment parameter based on an initial value of the compression parameter,
The optimal compression parameter is estimated using the adjustment parameter selected by the selection means, the initial value of the compression parameter, the size of the compressed data obtained by applying the initial value, and the target size, and the estimated compression A digital still camera, wherein compressed data of the image data is generated by applying a parameter. The digital still camera according to claim 1.
Information collecting means for collecting information indicating photographing conditions related to photographing processing by the photographing means;
Based on the information collected by the information collecting means, when it is determined that the photographing means is performing continuous photographing processing, the mode setting instruction indicating the continuous photographing mode is transmitted to the parameter calculating means and the input control. A digital still camera comprising mode setting means for inputting to the means. The digital still camera according to claim 8.
The information collecting means includes an interval collecting means for collecting a time interval related to acquisition of image data by the photographing means as information indicating photographing conditions,
The digital still camera according to claim 1, wherein the mode setting unit includes an interval determination unit that determines that the imaging unit is performing continuous imaging processing when the time interval is equal to or less than a predetermined threshold. The digital still camera according to claim 8.
The information collecting means includes sensitivity collecting means for collecting photographing sensitivity for each of the image data acquired by the photographing means as information indicating photographing conditions,
When the difference between the imaging sensitivity collected for the current frame by the sensitivity collection unit and the imaging sensitivity corresponding to the previous frame is equal to or less than a predetermined threshold, the mode setting unit performs continuous imaging processing. A digital still camera characterized by having a sensitivity judgment means for judging that it is in progress.

Images