JP2008312193A - Image data compressing device, image data compressing method, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image data compressing device, an image data compressing method, and program, for quickly recording JPEG data. <P>SOLUTION: The image data compressing device comprises a RAW compression processing part 57 for detecting high frequency component of image data, a JPEG parameter setting part 56 for calculating characteristic data (entropy) representing appearance frequency distribution of high frequency components, a JPEG parameter setting part 56 which calculates, based on the characteristic data, the coding amount predicted when an image data is compressed based on a first quantifying table, a JPEG parameter setting part 56 which calculates a second quantifying table for acquiring a target coding amount to be finally obtained at the RAW compression processing part 57, based on the target coding amount and predicted coding amount, and a JPEG processing part 53 for JPEG compression process based on the second quantifying table. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image data compression apparatus, an image data compression method, and a program.

  Some imaging devices such as single-lens reflex digital cameras are provided with an imaging mode capable of simultaneously recording reversibly compressed RAW image data and irreversibly compressed JPEG data. In order to record image data in this shooting mode, it is necessary to perform JPEG encoding processing as well as RAW data compression processing. In a system where JPEG encoding processing takes time, there is a high possibility that this JPEG processing time will become a bottleneck in recording time. In addition, in order to keep the JPEG code amount below a certain amount without degrading the image quality, it is necessary to perform the encoding process a plurality of times. Due to these circumstances, there is a problem that it takes a processing time until recording. It was.

Therefore, in order to solve the problem that processing time is required when RAW image data and JPEG data are recorded at the same time, Patent Document 1 discloses that JPEG files and JPEG images stored in RAW data are used in common. An imaging apparatus is disclosed in which the number of processing times is reduced.
JP 2006-229474 A

  According to Patent Document 1, it is possible to eliminate the need to generate a JPEG image for recording and JPEG data for display in a single shooting operation. However, in JPEG encoding processing, in order to compress the data to a predetermined data size, it is necessary to repeat a plurality of times, and JPEG data recording cannot be accelerated.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an image data compression apparatus, an image data compression method, and a program capable of speeding up the recording of JPEG data.

In order to achieve the above object, an image data compression apparatus according to a first invention includes an image processing unit that detects a high frequency component of image data, a calculation unit that calculates feature data representing an appearance frequency distribution of the high frequency component, A code amount prediction unit that calculates a prediction code amount when it is assumed that the image data is compressed based on the first quantization table, based on the feature data;
A quantization table generating unit that calculates a second quantization table for obtaining a target code amount to be finally obtained by the compression processing unit based on the target code amount and the predicted code amount; and A JPEG compression unit that performs JPEG compression processing based on the quantization table is provided.

In the image data compression apparatus according to the second invention, in the first invention, the high-frequency component in the image processing unit is a difference value of image data between neighboring pixels.
In the image data compression apparatus according to a third aspect of the present invention, in the first aspect, the feature data calculated by the calculation unit is a parameter i representing the magnitude of a high frequency component, and an appearance corresponding to the parameter i. When frequency is Pi
-ΣPi ・ LogPi
It is represented by

According to a fourth aspect of the present invention, there is provided an image data compression apparatus according to the first aspect, wherein the feature data is Eraw, and the predicted code amount when the JPEG compression processing is performed based on the first quantization table. Is Djpeg, and A, B, C, D, and E are constants.
Djpeg = A x Eraw + B
Or
Djpeg = C x Eraw2 + D x Eraw + E
There is a correlation.

An image data compression apparatus according to a fifth aspect of the present invention is the image data compression apparatus according to the first aspect, wherein the predicted code amount when the JPEG compression process is performed based on the first quantization table is Djpeg, and the quantization is performed. When the parameter is N, F and G are constants, and the target code amount when the JPEG compression processing is performed based on the quantization parameter N is Dtarget,
Dtarget = Djpeg × (F × 2- ^N + G)
And the first quantization table is Q1, the value of the second quantization table is Q2, and N is a quantization parameter,
Q2 = Q1 × 2- ^N
It is represented by

  The image data compression apparatus according to a sixth aspect of the present invention is the image data compression apparatus according to the first aspect, wherein the image data compression apparatus further encodes RAW data to generate variable length encoded data. It is characterized by having.

  An image data compression method according to a seventh aspect of the invention for achieving the above object comprises a step of detecting a high frequency component of the image data, a step of calculating feature data representing an appearance frequency distribution of the high frequency component, and the image data To calculate a prediction code amount based on the feature data, and to obtain a target code amount to be finally obtained by the compression processing unit. The second quantization table is calculated based on the target code amount and the predicted code amount, and JPEG compression processing is performed based on the second quantization table.

  An image data compression program to be executed by a computer according to an eighth invention for achieving the above object comprises a step of detecting a high frequency component of the image data, and a step of calculating feature data representing an appearance frequency distribution of the high frequency component. , A step of calculating a prediction code amount when it is assumed that the image data is compressed based on the first quantization table based on the feature data, and a target code to be finally obtained by the compression processing unit The method includes a step of calculating a second quantization table for obtaining the amount based on the target code amount and the predicted code amount, and a step of performing JPEG compression processing based on the second quantization table.

  To achieve the above object, an image data compression apparatus according to a ninth aspect of the present invention compresses image data by variable length coding based on a difference value between image data of adjacent pixels, and stores compression information related to image compression. A RAW compression processing unit to be obtained; a quantization parameter for performing quantization to obtain a target data size based on the compression information; and a Huffman for encoding data quantized by the quantization parameter. A JPEG parameter setting unit for setting a table; and a JPEG processing unit for performing JPEG compression processing on image data based on the quantization parameter and the Huffman table.

  In the image data compression apparatus according to a tenth aspect, in the ninth aspect, the compression information is entropy calculated based on the appearance frequency value of the difference value.

  To achieve the above object, an image data compression apparatus according to an eleventh aspect of the present invention reversibly compresses image data, and RAW compression processing unit for obtaining compression information related to image compression, and irreversibly compresses image data. And an irreversible compression processing unit and a parameter calculation unit for obtaining a parameter having a target data size based on the compression information.

An image data compression apparatus according to a twelfth aspect of the present invention is the image data compression apparatus according to the eleventh aspect of the invention, wherein entropy is calculated based on the compression information, and a target data size is obtained from the correlation between the entropy and the data size obtained by the irreversible compression processing. The above parameters are obtained.
An image data compression apparatus according to a thirteenth invention is characterized in that, in the eleventh invention, the entropy is data calculated based on an appearance frequency value of a high frequency component of the image data.

  In order to achieve the above object, an image data compression method according to a fourteenth aspect of the present invention compresses image data by variable length coding based on a difference value between image data of adjacent pixels, and stores compression information related to image compression. A step for obtaining, a quantization parameter for performing quantization to obtain a target data size based on the compression information, and a Huffman table for performing Huffman coding on the data quantized by the quantization parameter are set. And a step of performing JPEG compression processing on the image data based on the quantization parameter and the Huffman table.

  An image data compression program to be executed by a computer according to the fifteenth invention for achieving the above object compresses image data by variable length encoding based on a difference value between image data of adjacent pixels, and A step of obtaining compression information relating to compression, a quantization parameter for performing quantization to obtain a target data size based on the compression information, and Huffman coding of data quantized by the quantization parameter The Huffman table is set, and the image data is subjected to JPEG compression processing based on the quantization parameter and the Huffman table.

  According to the present invention, it is possible to provide an image data compression apparatus, an image data compression method, and a program that can speed up the recording of JPEG data.

  Hereinafter, a preferred embodiment using a digital single lens reflex camera to which the present invention is applied will be described with reference to the drawings. The digital single-lens reflex camera according to the present embodiment determines the composition of the subject and captures the subject image, and then performs various image processing on the image data before recording it on the image recording medium. In addition, as an image recording mode, it is possible to select a shooting mode in which irreversible compression processing by JPEG and reversible compression processing by RAW are performed and image data is recorded by both irreversible compression and lossless compression processing. .

  The electrical configuration of the digital single-lens reflex camera in this embodiment will be described with reference to FIG. A zoom lens system 1 for forming a subject image is attached to the camera body. The focal length of the zoom lens system 1 is variable, and driving for adjusting the focal length and the focal position is performed by a lens driving unit 9 having a motor or the like.

  An image sensor 3 is arranged on the optical axis of the zoom lens system 1 and in the vicinity of the imaging position of the subject image. The image sensor 3 photoelectrically converts the subject image and outputs an image signal. The output of the imaging device 3 is connected to an imaging circuit 5 that performs signal processing such as readout of image signals and amplification processing, and the output of the imaging circuit 5 is analog / digital (A / A) that performs AD conversion of the image signals. D) Connected to the converter 7.

  The A / D converter 7 is connected to a data bus 10, which includes a RAM (Random Access Memory) 11, a ROM (Read Only Memory) 13, an ASIC (Application Specific Integrated Circuit). Circuit) 15, system controller 20, drive controller 31, external I / F (interface) 37, video encoder 41, and LCD (Liquid Crystal Display) driver 45 are connected to each other. The RAM 11 is an electrically rewritable memory, and temporarily stores data. The ROM 13 is an electrically rewritable nonvolatile memory, and stores a program for controlling the digital single lens reflex camera, various adjustment values, and the like.

  The ASIC 15 is hardware for performing various processing such as image processing, JPEG compression / decompression processing, and RAW compression processing, and is connected to the system controller 20. The image compression processing in the ASIC 15 will be described later with reference to FIG. The system controller 20 is configured by a CPU (Central Processing Unit) or the like, and performs overall control of the digital single-lens reflex camera according to a program stored in the ROM 13.

  The system controller 20 is connected to the lens drive control circuit 21, the strobe light emission unit 23, the operation unit 25, and the power supply unit 27, and controls these circuits and the like. The lens drive control circuit 21 performs drive control of the lens drive unit 9 described above, and performs a focal length and a focusing operation of the zoom lens system 1. The strobe light emitting unit 23 projects illumination light toward the subject according to a control signal from the system controller 20.

  The operation unit 25 includes a power switch, a 1st release switch linked to the release button, a 2nd release switch, a shooting mode switch, a menu switch, a switch linked to various operation members such as a cross key for moving a cursor, and the like. Detects various settings and release operations by the photographer. The power supply unit 27 supplies power necessary for the operation of the digital single lens reflex camera, and includes a power supply battery, a voltage control circuit, and the like. The power supply unit 27 is provided with an external power supply input terminal 29 for receiving supply of external power such as a commercial power supply or a battery pack.

  A drive controller 31 is connected to the data bus 10 described above, and a disk drive 33 is connected to the drive controller 31. A recording medium 35 can be loaded in the disk drive 33. The recording medium 35 is a medium for recording image data that has been subjected to image processing by the ASIC 15 or the like, and performs recording control of the disk drive 33 by the drive controller 31.

  An external I / F 37 is connected to the data bus 10, and this external I / F 37 is connected to an external input / output terminal 39. The external I / F 37 is an interface for exchanging image data and other data with an external device such as a personal computer (PC).

  In addition, a video encoder 41 is connected to the data bus 10, and a video out 43 and an LCD driver 45 are connected to the video encoder 41. The video encoder 41 is a converter for converting into image data for display based on the image data stored in the RAM 11 or the recording medium 35, and the converted image data is transmitted via the video out 43. Are output to the outside and displayed on the LCD 47 by the LCD driver 45. The LCD 47 is arranged on the back surface of the digital single-lens reflex camera, and displays the subject images stored in the RAM 11 and the recording medium 35 and also displays various shooting modes and control values set by the operation unit 25.

  Next, RAW compression and JPEG compression in the ASIC 15 will be described with reference to FIG. The image signal output from the image sensor 3 is converted into digital RAW data (image data) by the A / D converter 7 and input to the ASIC 15 via the data bus 10. The block for compression shown in FIG. 2 includes path 1 for performing RAW compression processing and path 2 for performing JPEG processing.

  The RAW data input unit is connected to the image processing unit 51 constituting the path 2, and the output of the image processing unit 51 is connected to the JPEG processing unit 53. The RAW data input unit is also connected to the RAW compression processing unit 57 constituting the path 1, and the output of the RAW compression processing unit 57 is connected to the JPEG parameter setting unit 56. The JPEG processing unit 53 is connected to the output of the JPEG parameter setting unit 56. The image processing unit 51, JPEG processing unit 53, JPEG parameter setting unit 56, and RAW compression processing unit 57 are configured by hardware circuits.

  The RAW compression processing unit 57 in pass 1 performs reversible compression processing on the input RAW image data, obtains a difference value with an adjacent pixel at the time of compression processing, and calculates feature data representing an appearance frequency distribution of the difference value from this. To do. Details of the RAW compression processing unit 57 will be described later with reference to FIGS. 4 and 5. RAW compressed data is output from the output end of the RAW compression processing unit 57, and the above-described feature data is output to the JPEG parameter setting unit 56. The JPEG parameter setting unit 56 sets JPEG parameters using the feature data, and outputs them to the JPEG processing unit 53. Details of the JPEG parameter setting unit 56 will be described later with reference to FIGS.

  The image processing unit 51 in pass 2 performs correction such as white balance and image processing such as YC conversion on the input RAW image data. Details of the image processing unit 51 will be described later with reference to FIG. The JPEG processing unit 53 is a circuit for irreversibly compressing image data by the JPEG method, and performs compression using the compression parameter output from the JPEG parameter setting unit 56 when performing JPEG compression. Details of the JPEG processing unit 53 will be described later with reference to FIG.

  RAW compressed data is output from the above-described RAW compression processing unit 57 in pass 1, and JPEG compressed data is output from the JPEG processing unit 53 in pass 2. In other words, the RAW data based on the output of the image sensor 3 is irreversibly compressed and output as JPEG compressed data, and is reversibly compressed and output as RAW compressed data by the circuit shown in FIG.

  Next, the operation of the circuit for performing the compression processing in the ASIC 15 shown in FIG. 2 will be described with reference to FIGS. FIG. 3 shows the overall operation of the compression process. This flow is controlled by the system controller 20, and each process is executed by each circuit block in the ASIC 15.

  When the image compression process shown in FIG. 3 is started, it is determined whether or not there is RAW shooting (S1). In the digital single-lens reflex camera according to the present embodiment, the image data of the captured image is recorded on the recording medium 35 with JPEG compression. However, when the photographer operates the menu mode or the like, the RAW compressed data is also recorded. It is possible to record. In step S1, it is detected whether or not a shooting mode for simultaneously recording this RAW compressed data is set.

  If the result of detection in step S1 is RAW shooting mode, RAW compression processing unit 57 performs RAW compression processing (S3). At the time of RAW compression processing in this step, a difference value of image data between adjacent images is obtained, and compression information (frequency of appearance of difference values) is output therefrom. This RAW compression processing will be described later with reference to FIGS.

  When the RAW compression processing is completed, JPEG parameters are set (S5). In this JPEG parameter setting, a quantization parameter is calculated based on the compression information obtained by the RAW compression process, a Huffman table is created, and the compression parameter is output. This JPEG parameter setting will be described later with reference to FIGS.

  When the JPEG parameter setting in step S5 is completed, or if it is determined in step S1 that RAW shooting is not performed, image processing is performed next (S7). In this step, since correction processing such as white balance and the pixel array are Bayer arrays, RGB pixel outputs are subjected to interpolation calculation processing and YC conversion processing at the respective pixel positions. This image processing will be described later with reference to FIG.

  When the image processing in step S7 is completed, JPEG processing is next performed (S9). In JPEG processing, JPEG encoding is performed using the compression parameters set in step S5. This JPEG processing will be described later with reference to FIG.

  Next, the RAW compression process of step S3 is demonstrated using the flow shown in FIG. When the flow shown in FIG. 4 is entered, RAW compression processing is performed (S11). This RAW compression process executes the steps shown in FIG. First, using RAW data, a difference from adjacent pixels is obtained for all pixels (S21). This difference value corresponds to the high frequency component of the image. Subsequently, the appearance frequency of the obtained difference value is calculated (S23).

  Next, variable length coding is performed based on the difference value obtained in step S21 (S25). That is, although entropy coding is performed, in this embodiment, variable length coding based on Huffman code is performed.

  RAW compressed data is generated by variable length encoding in step S25. Returning to FIG. 4, subsequently, compression information is generated and output to the JPEG parameter setting unit 56 (S13, FIG. 4). In the present embodiment, the appearance frequency of the difference value calculated in step S23 is output as compressed information.

  Next, returning to FIG. 3, the setting of the JPEG parameter in step S5 will be described with reference to FIG. This JPEG parameter setting is executed by the JPEG parameter setting unit 56. First, compression information is input (S31). This is the information output in step S13 during RAW compression, and specifically the frequency of appearance of the difference value as described above.

When the compression information is input, the quantization parameter is calculated based on the compression information (S33). FIG. 7 shows the flow of the quantization parameter calculation. As shown in the flow of FIG. 7, first, entropy (feature data) is calculated from the magnitude of the high-frequency component, that is, the difference value of the image data between adjacent pixels and its appearance frequency (S41). Here, the entropy is, specifically, when a parameter representing the magnitude of the high-frequency component is i and the appearance frequency corresponding to the parameter i is Pi, -ΣPi · LogPi (Expression 1)
Calculated by

  Next, the prediction code amount for a predetermined entropy is calculated from the JPEG encoding size approximation formula (S43). That is, the relationship between entropy and JPEG encoding size has a certain correlation as shown in FIGS. The graphs of FIGS. 11 and 12 are experimental data created based on image data.

When this correlation is approximated by a linear equation as shown in FIG.
Djpeg = A x Eraw + B (Formula 2)
It becomes. here,
Eraw: entropy of RAW data Djpeg: prediction code amount in quantization table 1 (see Q table 1 in FIG. 13) A, B: constants.

Further, when the relationship between entropy and JPEG encoding size is approximated by a quadratic expression as shown in FIG.
Djpeg = C × Eraw ² + D × Eraw + E (Formula 3)
It becomes. However, C, D, and E are constants.

  In step S43, when the prediction code corresponding to the entropy of the image data is calculated by the approximate expression such as Expression 2 or Expression 3, next, the quantization parameter corresponding to the target coding size is calculated (S45). In JPEG compression, an image is divided into blocks, converted from a spatial domain to a frequency domain by discrete cosine transform in units of blocks, and the amount of information is reduced by quantizing the transformed data, and then entropy coding using Huffman codes is performed. Is doing. Therefore, in the present embodiment, the target data size is obtained by selecting a quantization parameter at the time of quantization.

As is well known, the quantization table (Q table) is a table of divisors for dividing and quantizing each DCT (Discrete Cosine Transform) coefficient obtained by discrete cosine transform in units of blocks by a predetermined value. Is. When the value of the Q table 1 in FIG. 13 is Q1 (where Q1 is a set of a plurality of values), the value of the Q table is set by arbitrarily setting the value of N
Q1 × 2- ^N (Formula 4)
When an arbitrary quantization table is generated and quantization is performed, the integer N is a quantization parameter.

There is a certain correlation between the JPEG encoding size and the quantization table as shown in FIG. Note that the Q tables 1 to 4 in FIG. 13 correspond to the quantization parameters N1, N2, N3, and N4, respectively. When this correlation is expressed by an approximate expression,
Dtarget = Djpeg × (F × 2- ^N + G) (Formula 5)
It becomes. here,
Dtarget: target code amount Djpeg: predicted JPEG code amount in quantization table 1 (Q table 1) N: quantization parameter F, G: constant

  Using the above approximate expression, a quantization parameter that is a target JPEG encoding size (predicted code amount) is calculated. The graph shown in FIG. 13 is experimental data created based on image data, and four lines are JPEG codes obtained by changing the quantization table (or quantization parameter) for each of the four types of images. Size. Although the values differ depending on the images, it can be seen that there is a certain correlation.

  Once the quantization parameter is calculated in step S45, the process returns to FIG. 6 to create a Huffman table (S35 in FIG. 6). FIG. 8 shows a flow for creating the Huffman table. First, entropy is calculated from the appearance frequency (S51). The entropy is calculated based on Equation 1 as in step S41, but the result obtained in step S41 is used as it is.

  Subsequently, a Huffman table is selected using this entropy (S53). That is, as shown in FIG. 14, there are two categories of Huffman tables, Huffman table 1 and Huffman table 2, and one of the Huffman tables is selected based on the entropy calculated by Equation 1. Here, the Huffman table 1 is used when the correlation between adjacent pixel outputs is strong like a natural image. On the other hand, the Huffman table 2 is used when the pixel output changes abruptly such as an artificial image such as a so-called sandstorm on a TV screen or an image obtained by capturing a fine lace with a black background. The table used.

  When the selection of the Huffman table is completed, the process returns to FIG. 6 and the compression parameter is output to the JPEG processing unit 53 (S37). Here, the compression parameters are the quantization parameter obtained in step S33 and the Huffman table selected in step S35.

  When the compression parameter output (S37) ends, the process returns to FIG. 3, and then the process proceeds to image processing in step S7 (see FIG. 3). The flow of this image processing will be described with reference to FIG. In the image processing section 51, first, image data correction processing is performed (S61). As correction processing, processing such as white balance and optical black is performed. Subsequently, a synchronization process is performed (S63). Since the RGB primary color filters are arranged in a Bayer array, the image sensor 3 obtains RGB values for each pixel by interpolation.

  When the synchronization processing is completed, image correction is performed next (S65). As image correction, corrections such as color reproducibility and gradation expression of image data are performed. When the image correction is completed, YC conversion is subsequently performed so as to obtain a YC signal composed of luminance and color information (S67). The processing in the steps so far has been processing of RGB pixel output based on the Bayer array, but here, JPEG compression or YC conversion to YC data that can be easily displayed on the LCD 47 is performed.

  When the YC conversion in step S67 ends, the process returns to FIG. 3 and proceeds to the JPEG process in step S9. The flow of this JPEG process will be described with reference to FIG. The JPEG processing unit 53 first inputs a compression parameter (S71). As described above, the compression parameter including the quantization parameter and the selected Huffman table is output in step S37 shown in the flow of FIG.

  Subsequently, JPEG encoding is performed using the input compression parameters (S73). Here, a new quantization table is generated from the quantization parameter N based on Expression (4), and the DCT coefficient is quantized using the newly generated quantization table. Next, the quantized DCT coefficient is Huffman-encoded based on the selected Huffman table to output compressed data having a target code amount. The above RAW compression processing and JPEG compression processing are processed in hardware by the blocks shown in FIG. 2, but may be processed in software by a CPU such as the system controller 20.

  As described above, in the image data compression apparatus according to the present embodiment, the image processing unit (S21, RAW compression processing unit 57) that detects the high-frequency component of the image data, and the feature that represents the appearance frequency distribution of the high-frequency component. A calculation unit (S41, JPEG parameter setting unit 56) for calculating data (entropy), and a prediction code amount when it is assumed that the image data is compressed based on the first quantization table, the characteristic data are also included. And a second quantization table for obtaining a target code amount to be finally obtained by the compression processing unit, the code amount prediction unit (S43, JPEG parameter setting unit 56), and the target code amount and the above A quantization table generating unit (S45, JPEG parameter setting unit 56) that calculates based on the predicted code amount, and a JPE based on the second quantization table. JPEG compression unit performs compression processing and a (S9, JPEG processing section 53).

  Therefore, in the present embodiment, the size of JPEG encoded data that is recorded at the same time can be predicted, and the recording speed of JPEG data can be increased. That is, since the JPEG encoded size can be predicted before compression, a quantization parameter having a specified size may be set. Since the JPEG compression process is not repeated until a predetermined size is achieved as in the prior art, JPEG data recording can be speeded up.

  In the present embodiment, the JPEG method has been described as the irreversible compression processing of image data, but other irreversible compression methods may be used. Further, although Huffman coding is used for the compression processing, the present invention is not limited to this, and other entropy codes may be used.

  Furthermore, in the present embodiment, the size of JPEG data is approximated by a linear expression or a quadratic expression as shown in FIGS. 11 and 12, but the approximate expression is not limited to this, and various expressions can be used. Can be used. In addition to the approximate expression, a table may be created and may be calculated by performing an interpolation calculation. Furthermore, in the present embodiment, information entropy is used as feature data representing the appearance frequency distribution of high-frequency components. However, the present invention is not limited to this, and a value indicating variance, for example, may be used.

  Furthermore, in the present embodiment, the application frequency of the difference value is used as the compressed data. However, the present invention is not limited to this. For example, the size of the variable length encoded data (S25 in FIG. 5) in the RAW compression processing unit. In this case, instead of the correlation between the entropy and the data size shown in FIGS. 11 and 12, based on the correlation between the size of the variable-length encoded data and the JPEG encoded size, The JPEG encoding size may be predicted.

  The present invention is not limited to a digital single-lens reflex camera, but can be applied to a digital camera of a compact type, for example. Furthermore, it can be applied to a camera that can be attached to a dedicated device such as a microscope photography apparatus. . In any case, the present invention can be applied to a camera that performs image data compression, an electronic imaging device, an image processing device, and the like.

1 is a block diagram showing an electrical configuration of a digital single-lens reflex camera according to an embodiment of the present invention. It is a block diagram regarding the compression process in ASIC concerning one Embodiment of this invention. It is a figure which shows the flow which shows the process of the image compression concerning one Embodiment of this invention. It is a figure which shows the flow of RAW compression concerning one Embodiment of this invention. It is a figure which shows the flow of the RAW compression process concerning one Embodiment of this invention. It is a figure which shows the flow of the JPEG parameter setting concerning one Embodiment of this invention. It is a figure which shows the flow of the quantization parameter calculation concerning one Embodiment of this invention. It is a figure which shows the flow of the Huffman table concerning one Embodiment of this invention. It is a figure which shows the flow of the image processing concerning one Embodiment of this invention. It is a figure which shows the flow of the JPEG process concerning one Embodiment of this invention. It is a figure which shows the correlation of the entropy and JPEG encoding size concerning one Embodiment of this invention. It is a figure which shows the correlation of the entropy and JPEG encoding size concerning one Embodiment of this invention. It is a figure which shows the correlation of the JPEG quantization table concerning one Embodiment of this invention, and a JPEG encoding size. It is a figure which shows the Huffman table concerning one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Zoom lens system, 3 ... Imaging element, 5 ... Imaging circuit, 7 ... Analog-digital (A / D) converter, 9 ... Lens drive part, 10 ... Data bus 11 ... RAM, 13 ... ROM, 15 ... ASIC, 20 ... system controller, 21 ... lens drive control circuit, 23 ... strobe light emission unit, 25 ... operation unit, 27 ... Power supply unit, 29 ... External power input terminal, 31 ... Drive controller, 33 ... Disk drive, 35 ... Recording medium, 37 ... External I / F, 39 ... External input / output terminal, 41 ... Video encoder, 43 ... Video out, 45 ... LCD driver, 47 ... Liquid crystal monitor (LCD), 51 ... Image processing unit, 53 ... JPEG processing 56, JPEG Meter setting unit, 57 ··· RAW compression processing unit

Claims (15)

An image processing unit for detecting high-frequency components of the image data;
A calculation unit for calculating feature data representing the appearance frequency distribution of the high-frequency component;
A compression processing unit that compresses the image data based on a quantization table and a Huffman coding table;
A code amount prediction unit that calculates a prediction code amount when it is assumed that the image data is compressed by the compression processing unit based on a first quantization table;
A quantization table generating unit that calculates a second quantization table for obtaining a target code amount to be finally obtained by the compression processing unit based on the target code amount and the predicted code amount;
A JPEG compression unit that performs JPEG compression processing based on the second quantization table;
An image data compression apparatus comprising:   The image data compression apparatus according to claim 1, wherein the high-frequency component in the image processing unit is a difference value of image data between neighboring pixels. When the characteristic data calculated by the calculation unit is i indicating a parameter representing the magnitude of the high frequency component and Pi representing the appearance frequency corresponding to the parameter i,
-ΣPi ・ LogPi
The image data compression apparatus according to claim 1, wherein When the feature data is Eraw, the prediction code amount when the JPEG compression processing is performed based on the first quantization table is Djpeg, and A, B, C, D, and E are constants,
Djpeg = A x Eraw + B
Or
Djpeg = C × Eraw2 + D × Eraw + E
The image data compression apparatus according to claim 1, wherein: The prediction code amount when the JPEG compression processing is performed based on the first quantization table is Djpeg, the quantization parameter is N, F and G are constants, and the quantization parameter N is based on the quantization parameter N. When the target code amount when performing the JPEG compression process is Dtarget,
Dtarget = Djpeg × (F × 2- ^N + G)
And
When the first quantization table is Q1, the value of the second quantization table is Q2, and N is a quantization parameter,
Q2 = Q1 × 2- ^N
The image data compression apparatus according to claim 1, wherein   2. The image data compression apparatus according to claim 1, further comprising a variable length encoding unit that encodes RAW data and generates variable length encoded data. Detecting a high frequency component of the image data;
Calculating feature data representing the appearance frequency distribution of the high-frequency component;
A step of calculating a predictive code amount based on the feature data when it is assumed that the image data is compressed by a compression processing unit based on a first quantization table;
Calculating a second quantization table for obtaining a target code amount to be finally obtained by the compression processing unit based on the target code amount and the predicted code amount;
Performing JPEG compression processing based on the second quantization table;
An image data compression method comprising: Detecting a high frequency component of the image data;
Calculating feature data representing the appearance frequency distribution of the high-frequency component;
A step of calculating a predictive code amount based on the feature data when it is assumed that the image data is compressed by a compression processing unit based on a first quantization table;
Calculating a second quantization table for obtaining a target code amount to be finally obtained by the compression processing unit based on the target code amount and the predicted code amount;
Performing JPEG compression processing based on the second quantization table;
Is an image data compression program that causes a computer to execute. A RAW compression processing unit that compresses image data by variable length coding based on a difference value between image data of adjacent pixels and obtains compression information related to image compression;
JPEG parameter setting for setting a quantization parameter for performing quantization to obtain a target data size based on the compression information and a Huffman table for performing Huffman coding on data quantized by the quantization parameter And
A JPEG processing unit that performs JPEG compression processing on the image data based on the quantization parameter and the Huffman table;
An image data compression apparatus comprising:   The image data compression apparatus according to claim 9, wherein the compression information is entropy calculated based on an appearance frequency value of the difference value. A RAW compression processing unit that reversibly compresses image data and obtains compression information related to image compression;
An irreversible compression processing unit for irreversibly compressing image data;
A parameter calculation unit for obtaining a parameter that is a target data size based on the compression information;
And the irreversible compression processing unit performs irreversible compression processing based on the parameters.   12. The image data according to claim 11, wherein entropy is calculated based on the compression information, and the parameter having a target data size is obtained from a correlation between the entropy and the data size obtained by the lossy compression processing. Compression device.   12. The image data compression apparatus according to claim 11, wherein the entropy is data calculated based on an appearance frequency value of a high frequency component of the image data. Compressing the image data by variable length coding based on the difference value between the image data of adjacent pixels, and obtaining compression information related to the image compression;
Setting a quantization parameter for performing quantization to obtain a target data size based on the compression information, and a Huffman table for performing Huffman coding on data quantized by the quantization parameter;
Performing JPEG compression on the image data based on the quantization parameter and the Huffman table;
An image data compression method comprising: Compressing the image data by variable length coding based on the difference value between the image data of adjacent pixels, and obtaining compression information related to the image compression;
Setting a quantization parameter for performing quantization to obtain a target data size based on the compression information, and a Huffman table for performing Huffman coding on data quantized by the quantization parameter;
Performing JPEG compression on the image data based on the quantization parameter and the Huffman table;
A program that causes a computer to execute.