JP2006352335A - Image coding equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problems of a decrease in the response of equipment and a decrease in successive photographing speed/number of successive photographing frames since coding must be tried by the number of a plurality of coding parameters held by a storage means and hence processing time per image data becomes long. <P>SOLUTION: Coding processing is made by selecting the same coding parameter continuously when the free space of a memory that can be used for performing the loss-less compression processing of image data is equal to or higher than a threshold. Conversely, a coding parameter where the amount of coding becomes the smallest is selected from a plurality of coding parameters for performing the coding processing when the free space is less than the threshold. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image encoding apparatus that encodes image data and records the image data on a recording medium.

  An image captured by an image sensor in an image processing apparatus such as an electronic camera is A / D converted into digital data. In many cases, necessary image processing is performed and then irreversible compression conversion such as JPEG encoding is performed. Thus, an efficient image is recorded on the recording medium.

  In addition, when more importance is attached to image quality, all information obtained from the image sensor is recorded after reversible compression conversion is performed on the recording medium without performing any image processing inside the image processing apparatus such as an electronic camera. The recorded image data is subjected to higher quality image processing by computer software or the like provided by the apparatus manufacturer, thereby providing the user with an image with better image quality.

  Conventionally, in lossless compression, in many cases, an efficient encoding to a recording medium can be achieved by selecting and applying a suitable encoding parameter from among a plurality of encoding parameters so that the encoded data size is minimized. The image is recorded. For example, Patent Document 1 proposes a technique of trying encoding with a plurality of encoding parameters held in a storage unit one by one and employing an encoding parameter having a minimum encoded data size. .

Further, in Patent Document 2, when it is determined that the buffer memory for holding the image data is full of image data that has not been subjected to compression processing when performing high-speed continuous shooting, and there is no free space, A method for compressing image data and storing it in a recording medium has been proposed.
JP2001-326939 JP 07-099629

  However, in the prior art of Patent Document 1, encoding must be attempted by the number of the plurality of encoding parameters held in the storage unit, and the processing time per image data becomes long. There was a problem that the response and the continuous shooting speed / number of frames were reduced.

  In the prior art of Patent Document 2, the data size of the compressed image data is not considered. Since the writing speed to the recording medium is slower than the buffer memory, it takes time until the image data in the buffer memory is written to the recording medium and the buffer memory is freed, resulting in a decrease in the continuous shooting speed. It was.

In order to achieve the object of the present invention, an image encoding apparatus of the present invention comprises the following arrangement. That is, an encoding unit that encodes image data with an encoding parameter, a storage unit that holds a plurality of the encoding parameters, a memory area for encoding image data, and a plurality of units that are held in the storage unit Parameter selection means that uses an optimal encoding parameter for encoding image data from the encoding parameters of
Whether to encode image data using a plurality of encoding parameters held in the storage means and select optimal encoding data among them, or to encode using predetermined encoding parameters An image encoding apparatus comprising a determining unit for determining.

  When performing reversible compression processing of image data in the image encoding device inside the electronic camera during continuous shooting, if the memory area required to process the image data is greater than or equal to the threshold value, the previous image data is stored in the memory area. Since the next image data can be processed as it is, the continuous shooting speed of the electronic camera depends on the speed of writing the image data into the memory. In this case, the continuous shooting speed of the electronic camera can be increased by performing the lossless compression process only once using the same encoding parameter regardless of the characteristics of the image data and shortening the time required for the compression process.

  When the memory area necessary for processing the image data is less than the threshold value, the image processing device in the electronic camera immediately writes the reversibly compressed image data on the recording medium to process the next image data. It is necessary to secure a memory area. Even in this case, if the time taken to perform reversible compression processing of image data once is sufficiently faster than the time for writing the compressed data to the recording medium, the reversible compression processing of the image data is performed using a plurality of encoding parameters. Writing compressed data with a small code amount on the recording medium can shorten the writing time, shorten the time until the next CCD-RAW data can be written in the memory area, and increase the continuous shooting speed.

  In addition, when image data is taken continuously by an electronic camera, the image data has a feature with high similarity. Therefore, the first image data taken by continuous shooting is losslessly compressed using a plurality of encoding parameters, the encoding parameter with the smallest code amount is selected, and the encoding parameters are taken continuously 2 By applying it to the image data of the second and subsequent sheets, it is possible to reduce the code amount of the image data of the second and subsequent sheets and increase the number of continuous shot frames.

(First embodiment)
FIG. 1 is a diagram illustrating a schematic configuration of an imaging apparatus when the imaging apparatus is used in the present embodiment as an image processing apparatus having functions of an image encoding apparatus and an image decoding apparatus. In the figure, reference numeral 100 denotes an image pickup apparatus. When the main image is reversibly compressed and recorded, image data taken by the image pickup device is obtained using a Huffman encoding / decoding circuit in the baseline JPEG circuit. A case where reversible compression / recording is performed without performing any image processing will be described.

  Reference numeral 10 denotes an imaging lens that optically forms a photographic image, 12 denotes an imaging device that converts the photographic image into an analog electrical signal, and 14 denotes an A / D converter that converts an analog signal output from the imaging device 12 into a digital signal. is there. Here, the digital data output from the A / D converter 14 is hereinafter referred to as CCD-RAW data.

  Reference numeral 16 denotes a D / A converter, and 18 denotes an image display unit comprising a TFT LCD or the like. The display image data written in the memory 40 is converted from digital data to analog data via the D / A converter 16 and displayed by the image display unit 18.

  Reference numeral 20 denotes a recording medium such as a memory card or a hard disk, and photographed image data and the like are recorded on the recording medium 20.

  Reference numeral 30 denotes an image processing circuit, which performs development processing such as predetermined pixel interpolation processing and color conversion processing, and resizing processing on CCD-RAW data that has been shot or recorded.

  Reference numeral 40 denotes a memory for temporarily storing captured image data, which has a recording capacity sufficient to store a predetermined number of still images and a moving image for a predetermined time. For example, digital image data output from the A / D converter 14 is written into the memory 40 via the memory control circuit 50, the image processing circuit 30, or directly via the memory control circuit 50.

  A memory control circuit 50 controls the data flow to the A / D converter 14, D / A converter 16, recording medium 20, image processing circuit 30, memory 40, DPCM conversion circuit 80, and JPEG circuit 60.

  Reference numeral 60 denotes a JPEG circuit that compresses / decompresses image data by the baseline JPEG method, and includes a DCT conversion circuit 62, a quantization circuit 64, a MUX (data selector) 66, and a Huffman encoding / decoding circuit 68. The data selector 66 switches between JPEG encoding / decoding and CCD-RAW data lossless compression / expansion.

  Reference numeral 70 denotes a MUX (data selector) that switches between JPEG encoding / decoding and lossless compression / decompression of CCD-RAW data.

  A circuit 80 performs DPCM conversion on CCD-RAW data in order to perform lossless compression / decompression processing of CCD-RAW data using the Huffman encoding / decoding circuit 68 of the JPEG circuit 60. The DPCM conversion circuit 80 performs DPCM conversion (predictive encoding) of CCD-RAW data in order to reduce the entropy of the information source and increase the encoding efficiency in the Huffman encoding. The DPCM conversion circuit 80 performs, for example, DPCM conversion (predictive coding) on 10-bit CCD-RAW data and inverse DPCM conversion on 11-bit DPCM data.

  DPCM conversion utilizes the fact that image information has a strong correlation with surrounding pixels, and converts it into a difference value between the pixel data of an adjacent pixel (the pixel on the left) and the pixel data of the pixel to be encoded. By reducing the entropy of, the coding efficiency in Huffman coding can be increased. In the present embodiment, in consideration of the CCD color filter array as shown in FIG. 2, the difference value with the pixel data adjacent to the left by two pixels is always calculated. Therefore, the DPCM conversion circuit 80 is configured to obtain a difference between the input CCD-RAW data and the CCD-RAW data input two times before.

  Reference numeral 90 denotes a system control circuit that controls the operation of the entire image capturing apparatus 100 and each circuit constituting the image capturing apparatus 100 according to the setting by the mode dial switch 92 and according to the contents stored in the ROM 96 (read only memory).

  Reference numeral 92 denotes a mode dial switch, which can switch and set each function mode such as power-off, shooting mode, and playback mode.

  A read-only memory (ROM) 96 stores a program used by the system control circuit 50 and a quantization table and a Huffman table set in the JPEG circuit 60 in advance.

  In the present embodiment, during continuous shooting, image data captured by the image sensor 12 via the lens 10 is converted into digital data by the A / D converter 14, and sequentially stored as CCD-RAW data in the memory 40 by the memory control circuit 50. Buffered.

  In addition, since the lossless compression process is executed by sequentially reading out the buffered CCD-RAW data in the memory 40, the imaging process and the lossless compression process are performed asynchronously.

  In this embodiment, the procedure of the lossless compression process is changed according to the conditions, but the imaging process is not changed. Therefore, the lossless compression process will be described below with reference to FIG.

  It is assumed that the Huffman table used for the lossless compression process is statistically calculated in advance and held in the encoding parameter storage unit. A plurality of Huffman tables are recorded in the memory 96 in advance. A plurality of Huffman tables are Huffman tables generated from an average histogram of image data having highly similar features, and perform efficient encoding processing on image data having similar similarities. I can do it.

  First, before starting the reversible compression process of CCD-RAW, the free capacity of the memory 40 that can be used for the reversible compression process of the next CCD-RAW data is checked (S101). One of the following two types of processing is selected according to the free space available for the lossless compression processing of the CCD-RAW data.

  When the free capacity of the memory 40 that can be used for the lossless compression processing of the CCD-RAW data is equal to or larger than the threshold value, No is selected in S101, and the Huffman table used for the lossless compression processing is set in the JPEG circuit 60 (S102).

  In S101, the threshold value is changed according to the writing speed to the recording medium. When the writing speed to the recording medium is fast, the threshold value is reduced, and when the writing speed is slow, the threshold value is increased.

  The Huffman table set in S102 is always the same Huffman table regardless of the characteristics of the CCD-RAW data. This Huffman table is an encoding parameter that reduces the average code amount when image data having different characteristics is encoded, and is calculated in advance. This Huffman table is also recorded in the memory 96 in advance.

  The CCD-RAW data held in the memory 40 is transferred to the DPCM conversion circuit 80 via the memory control circuit 50 (S103). The transferred CCD-RAW data is subjected to DPCM conversion in the DPCM conversion circuit 80 (S104), and the baseline JPEG Huffman encoding / decoding circuit 68 in the JPEG circuit 60 is subjected to Huffman encoding processing (S105). The data is transferred to the memory 40 via the control circuit 50 (S106).

  When the reversible compression processing of the CCD-RAW data is started (S101), if the available free space in the memory 40 is less than the threshold value, Yes is selected in S101. Next, the system control circuit 90 selects one of the Huffman tables stored in the memory 96 and sets it in the JPEG circuit 60 (S110), and performs memory control on the CCD-RAW data held in the memory 40. The data is transferred to the DPCM conversion circuit 80 via the circuit 50 (S111). The transferred CCD-RAW data is subjected to DPCM conversion in the DPCM conversion circuit 80 (S112), and the baseline JPEG Huffman encoding / decoding circuit 68 in the JPEG circuit 60 is subjected to Huffman encoding processing (S113). The data is transferred to the memory 40 via the control circuit 50 (S114).

  The system control circuit 90 compares the code amount of the Huffman-encoded data held in the memory 40 with the code amount of the previously encoded data (S115). As a result of the code amount comparison, encoded data with a small code amount is selected (S116), and the selected encoded data is held in the memory 40 as it is. The encoded data not selected is deleted or used as an area for storing the next encoded data.

  It is determined whether or not all the encoding processes described above using a plurality of Huffman tables stored in advance in the memory 96 have been completed (S117). If all have not been completed, the next Huffman table in the memory 96 is stored in the JPEG circuit 60. (S110), and the processes after S110 are repeated.

  Finally, the encoded data with the smallest code amount is held in the memory 40.

  For example, the time required for one encoding is 500 ms, the writing speed to the recording medium is 1 MB / second, and encoding is performed using a plurality of Huffman tables, so that the code amount of image data is changed from 8 Mbytes to 6 Mbytes. If it is reduced, the writing time to the recording medium is reduced by 2 seconds, so even if the encoding is performed three times, it takes only 1500 ms, so the overall recording time is shortened by 500 ms.

  Further, as described above, one of the two processes described above is not selected according to the free space of the memory 40, but the image data remaining on the memory 40 has not yet been written to the recording medium. When the number of image data is equal to or greater than the threshold, control may be performed so as to select the encoding process using the plurality of Huffman tables described above. In this case, the threshold value is increased when the writing speed to the recording medium is high, and the threshold value is decreased when the writing speed is low.

(Second Embodiment)
Next, a second embodiment of the present invention will be described.

  Since the configuration of the second embodiment is basically the same as the configuration of the first embodiment, the description of the first embodiment is used in the description of the second embodiment. Only the differences are explained.

  The flow of processing in this embodiment will be described with reference to FIG.

  Assume that CCD-RAW data to be subjected to reversible compression processing is taken continuously by an electronic camera.

  If the CCD-RAW data to be subjected to the reversible compression processing is the first image data of the image data taken by the electronic camera, Yes is selected in S200. Next, the system control circuit 90 selects one of the Huffman tables stored in the memory 96 and sets it in the JPEG circuit 60 (S210), and the CCD-RAW data held in the memory 40 is controlled by the memory. The data is transferred to the DPCM conversion circuit 80 via the circuit 50 (S211). The transferred CCD-RAW data is subjected to DPCM conversion in the DPCM conversion circuit 80 (S212), and the baseline JPEG Huffman encoding / decoding circuit 68 in the JPEG circuit 60 performs Huffman encoding processing (S213). The data is transferred to the memory 40 via the control circuit 50 (S214).

  The system control circuit 90 compares the code amount of the Huffman-encoded data held in the memory 40 with the code amount of the previously encoded data (S215). As a result of the code amount comparison, encoded data with a small code amount is selected (S216), and the selected encoded data is held in the memory 40 as it is. The encoded data not selected is deleted or used as an area for storing the next encoded data.

  It is determined whether or not all the encoding processes described above using a plurality of Huffman tables stored in advance in the memory 96 have been completed (S217). If all have not been completed, the next Huffman table in the memory 96 is stored in the JPEG circuit 60. (S210), and the processes after S210 are repeated.

  Finally, the encoded data with the smallest code amount is held in the memory 40.

  If the CCD-RAW data to be subjected to the reversible compression process is the second or later image data of the image data taken by the electronic camera, No is selected in S200. Next, a free area that can be used for the reversible compression processing of the CCD-RAW is checked in the memory 40 (S201).

  In S201, the threshold is changed according to the writing speed to the recording medium. When the writing speed to the recording medium is fast, the threshold value is reduced, and when the writing speed is slow, the threshold value is increased.

  Subsequently, the system control circuit 90 selects the Huffman table used for Huffman encoding the first piece of image data taken continuously and sets it in the JPEG circuit 60 (S202) and stores it in the memory 40. The obtained CCD-RAW data is transferred to the DPCM conversion circuit 80 via the memory control circuit 50 (S203). The transferred CCD-RAW data is subjected to DPCM conversion in the DPCM conversion circuit 80 (S204), Huffman encoding processing is performed in the baseline JPEG Huffman encoding / decoding circuit 68 in the JPEG circuit 60 (S205), and the memory The data is transferred to the memory 40 via the control circuit 50 (S206).

  Also, a free area that can be used for the reversible compression processing of the CCD-RAW in the memory 40 is checked (S201), and if the free capacity is less than the threshold value, Yes is selected in S101. In this case, as in the case where the CCD-RAW data to be subjected to the above-described lossless compression processing is the first image data taken continuously by the electronic camera, the image of the plurality of Huffman tables is used. The Huffman encoding process is performed using the Huffman table with the smallest data code amount.

  For example, in the case where image data is always encoded using the same Huffman table regardless of image characteristics, the second and subsequent images can be encoded by encoding with the Huffman table optimal for the first image data in continuous shooting. Assuming that the average code amount of image data has decreased from 8 Mbytes to 6 Mbytes, if there is a 64 Mbyte memory area that can be used for lossless compression processing of CCD-RAW data, 8 to 10 image images can be recorded during continuous shooting. It increases to.

  Furthermore, as described above, one of the two processes described above is not selected according to the free space of the memory 40, but the image data remaining on the memory 40 has not yet been written to the recording medium. When the number of image data is equal to or greater than the threshold, control may be performed so as to select the encoding process using the plurality of Huffman tables described above. In this case, the threshold value is increased when the writing speed to the recording medium is high, and the threshold value is decreased when the writing speed is low.

1 is a schematic diagram of an imaging apparatus in an embodiment of the present invention. FIG. 3 is a diagram illustrating a color filter array of an image sensor. 5 is a flowchart showing a procedure for the imaging apparatus 100 according to the first embodiment of the present invention to create a CCD-RAW reversible compressed image from CCD-RAW data. 10 is a flowchart illustrating a procedure in which the imaging apparatus 100 according to the second embodiment of the present invention creates a CCD-RAW lossless compressed image from CCD-RAW data.

Claims (12)

Encoding means for encoding image data with encoding parameters, storage means for holding a plurality of the encoding parameters, and a memory area used for recording captured image data or encoded image data An image encoding control method applied to an image encoding apparatus having parameter selection means that uses an optimal encoding parameter for encoding image data from a plurality of encoding parameters held in the storage means. And
Decide whether to encode image data using a plurality of encoding parameters stored in the memory area and select encoded data from among them, or to encode using predetermined encoding parameters An image coding control method comprising a determination step.   Selecting an encoding parameter with the smallest code amount from a plurality of encoding parameters held in the storage means when the free space in the memory area usable for encoding image data is less than a threshold; 2. The image encoding control method according to claim 1, wherein the same encoding parameter is always selected when the free space of the memory area usable for encoding image data is equal to or greater than a threshold value.   3. The image encoding control method according to claim 1, wherein the threshold value according to claim 2 is decreased when the writing speed to the recording medium is high and is increased when the writing speed is low.   When the number of image data not yet written to the recording medium among the image data held in the memory area is equal to or greater than a threshold value, the code amount is the smallest among the plurality of encoding parameters held in the storage unit The image encoding control method according to claim 1, wherein an encoding parameter is selected, and the same encoding parameter is selected whenever the encoding parameter is less than a threshold value.   5. The image encoding control method according to claim 1, wherein the threshold value according to claim 4 is increased when the writing speed to the recording medium is high and is decreased when the writing speed is low.   When the image data to be encoded is the first piece of image data taken by continuous shooting among the image data taken by continuous shooting, from the plurality of encoding parameters held in the storage means Select the encoding parameter with the smallest code amount, and if the image data to be encoded is the second or later image data taken continuously, one piece of image data taken continuously 2. The image encoding control method according to claim 1, wherein an encoding parameter used for the eyes is selected. Encoding means for encoding image data with encoding parameters, storage means for holding a plurality of the encoding parameters, and a memory area used for recording captured image data or encoded image data A parameter selection unit that uses an optimal encoding parameter for encoding image data from a plurality of encoding parameters held in the storage unit;
Selection means for selecting whether to encode image data from a plurality of encoding parameters held in the storage means and to select encoded data from among them, or to encode using predetermined encoding parameters An image encoding apparatus comprising:   Selecting an encoding parameter with the smallest code amount from a plurality of encoding parameters held in the storage means when the free space in the memory area usable for encoding image data is less than a threshold; 8. The image encoding apparatus according to claim 7, further comprising a selection unit that selects the same encoding parameter whenever the free space in the memory area that can be used for encoding image data is equal to or greater than a threshold value. .   9. The image encoding control method according to claim 7, wherein the threshold value according to claim 8 is decreased when the writing speed to the recording medium is high, and is increased when the writing speed is low.   Of the image data held in the memory area, when the number of image data not yet written on the recording medium is equal to or greater than the threshold, the code amount is the smallest among the plurality of encoding parameters held in the storage means 8. The image encoding apparatus according to claim 7, further comprising: a selection unit that selects an encoding parameter to be selected and always selects the same encoding parameter when the encoding parameter is less than a threshold value.   11. The image coding control method according to claim 1, wherein the threshold value according to claim 10 is increased when the writing speed to the recording medium is high, and is decreased when the writing speed is slow.   When the image data to be encoded is the first piece of image data taken by continuous shooting among the image data taken by continuous shooting, from the plurality of encoding parameters held in the storage means Select the encoding parameter with the smallest code amount, and if the image data to be encoded is the second or later image data taken continuously, one piece of image data taken continuously 8. The image encoding apparatus according to claim 7, further comprising: a selection unit that selects an encoding parameter used for an eye.

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