WO2013153761A1

WO2013153761A1 - Image decoding apparatus, image decoding method, and program

Info

Publication number: WO2013153761A1
Application number: PCT/JP2013/002167
Authority: WO
Inventors: Masato Shima; Mitsuru Maeda
Original assignee: Canon Kabushiki Kaisha
Priority date: 2012-04-13
Filing date: 2013-03-29
Publication date: 2013-10-17
Also published as: JP2013223035A

Abstract

An image decoding method includes decoding blocks coded in a first coding mode where a prediction is conducted and decoding blocks coded in a second coding mode without the prediction, in which the decoding the blocks coded in the first coding mode includes generating a first reproduction image from reproduced prediction errors and prediction results, and the decoding the blocks coded in the second coding mode includes generating a second reproduction image by, when a bit depth of pixel information of the block coded in the second coding mode is smaller than that of an output image, reproducing output pixel tentative values through pixel information bit shift on the basis of a difference between the bit depth of the output image and that of the pixel information and correcting the output pixel tentative values by the difference to calculate output pixel values.

Description

IMAGE DECODING APPARATUS, IMAGE DECODING METHOD, AND PROGRAM

The present invention relates to an image decoding apparatus, an image decoding method, a program, and image coding data. The invention particularly relates to decoding processing with respect to an uncompressed coding block.

H.264/MPEG-4 AVC (hereinafter, which will be abbreviated as H.264) is proposed as a coding system for video image compression recording (see NPL 1).

In H.264, it is possible to use a technology called I_PCM with which an input pixel is included in a bit stream as it is without compression.

In recent years, activities for international standardization of a coding system having a still higher efficient have started as a successor technology of H.264. JCT-VC (Joint Collaborative Team on Video Coding) has been established between ISO/IEC and ITU-T, and the standardization has advanced as an HEVC (High Efficiency Video Coding) system (hereinafter, which will be referred to as HEVC). Similarly as in H.264, I_PCM may also be used. A further exists in that pixel data for the number of bits smaller than a bit depth of an input image may be included in the bit stream (see NPL 2).

Fig. 5 illustrates a configuration example of the bit stream. In HEVC, a bit_depth_luma_minus8 code and a bit_depth_chroma_minus8 code represents pixel depth information in a header called seq_parameter_set header. For depth information of an I_PCM coding pixel (hereinafter, which will be referred to as PCM pixel depth information), a pcm_bit_depth_luma_minus1 code and a pcm_bit_depth_chroma_minus1 code exists. Picture data where respective pictures are coded follows the header data. In the picture data, coding data of the pixels that have been subjected to the I_PCM coding and coding data of the pixels where the coding is conducted through a prediction.

In HEVC, in a case where the pixel data having the number of bits smaller than the bit depth of the input image is included, correction processing is conducted on a decoding side so that the pixel data having the fewer number of bits is set to have the same bit depth as the bit depth of the input image. In HEVC, decoding processing in I_PCM using the fewer number of bits is realized through a correction by conducting a bit shift of the pixel data by the number corresponding to a difference between the bit depth of the input image and the number of bits of the pixel data included in the bit stream.

However, since the correction is conducted only through the bit shift, a maximum value of the pixel data after the correction is smaller than a maximum value of the input image by the number of lower bits generated through the bit shift. In a case where a value of the PCM pixel depth information is 1 and a value of the pixel depth information is 8, for example, a value of the information that has been subjected to the PCM coding is 0 or 1. With regard to a corresponding reproduction pixel, a reproduction pixel value is 0 in a case where the value of the information that has been subjected to the PCM coding is 0, and the reproduction pixel value is 128 in a case where the value of the above-described information is 1.

Since a median of the pixel data after the correction is different from a median of the input image, a problem of a pixel reproducibility occurs.

ITU-T H.264 (03/2010) Advanced video coding for generic audiovisual services JCT-VC contributed article, JCTVC-H1003, the internet <http://phenix.int-evry.fr/jct/doc_end_user/documents/8_San%20Jose/wg11/>

In view of the above, the present invention has been made to solve the above-described problems and aims at avoiding a pixel degradation by conducting an appropriate correction in decoding processing in I_PCM using a fewer number of bits.

To solve the above-described problems, an image decoding method of decoding a bit stream and reproducing an image according to an aspect of the present invention includes: decoding blocks coded in a first coding mode in which a prediction is conducted; and decoding blocks coded in a second coding mode in which the prediction is not conducted, in which the decoding the blocks coded in the first coding mode includes conducting a first reconstruction of generating a first reproduction image from reproduced prediction errors and results of the prediction, and the decoding the blocks coded in the second coding mode includes conducting a second reconstruction of generating a second reproduction image by, in a case where a bit depth of pixel information of the block coded in the second coding mode is smaller than a bit depth of an output image, reproducing output pixel tentative values through a bit shift of the pixel information on the basis of a difference between the bit depth of the output image and the bit depth of the pixel information and correcting the output pixel tentative values on the basis of the difference between the bit depths to calculate output pixel values.

According to the aspect of the present invention, it is possible to conduct the decoding processing in which the pixel degradation is suppressed even in I_PCM where a fewer of number of bits are used, and the image quality of the decoded image may further be improved.

Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

Fig. 1 is a block diagram of a configuration of an image decoding apparatus according to a first exemplary embodiment. Fig. 2 is a block diagram of a detail of a second image decoding and reproduction unit according to the first exemplary embodiment. Fig. 3 is a flow chart of an image decoding processing in the image decoding apparatus according to the first exemplary embodiment. Fig. 4 is a block diagram of a hardware configuration example of a computer applicable to the image decoding apparatus according to embodiments of the present invention. Fig. 5 illustrates an example of a bit stream structure decoded by the decoding apparatus. Fig. 6 is a block diagram of a configuration of an image decoding apparatus according to a second exemplary embodiment. Fig. 7 is a flow chart of an image decoding processing in the image decoding apparatus according to the second exemplary embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Configurations according to the following embodiments are merely examples, and the present invention is not limited to the illustrated configurations.

First exemplary embodiment

Fig. 1 is a block diagram of a configuration of an image decoding apparatus according to a first exemplary embodiment of the present invention. Decoding of a bit stream illustrated in Fig. 5 will be described as an example according to the present embodiment. It is noted that the bit stream to be decoded is not limited to this.

A coded bit stream is input to a terminal 101. A separate decoding unit 102 is configured to separate information related to decoding processing and coding data related to coefficients from the bit stream and also decode coding data existing in a header part of the bit stream. A first decoding unit 103 is configured to decode predictive coding pixel information that is output from the separate decoding unit 102 to reproduce a quantization parameter, quantization coefficients, and prediction information. An inverse quantization and inverse transform unit 104 is configured to input the quantization coefficients in units of block, perform inverse quantization by the reproduced quantization parameter to obtain transform coefficients, and perform inverse orthogonal transform to reproduce prediction errors. A frame memory 107 stores the reproduced picture image data. A first image reproduction unit 105 is configured to generate prediction image data by appropriately referring to the frame memory 107 on the basis of the prediction information. Reproduction image data is reproduced from this prediction image data and the prediction errors reproduced by the inverse quantization and inverse transform unit 104 to be output. A second image decoding and reproduction unit 106 is configured to reproduce the reproduction image data from PCM pixel information to be output by using pixel depth information and PCM pixel depth information output from the separate decoding unit 102. The reproduced image data is output to an external part from a terminal 108.

An image decoding operation in the image decoding apparatus will be described below. In Fig. 1, the bit stream input from the terminal 101 is input to the separate decoding unit 102. The separate decoding unit 102 separates the information related to the decoding processing and the coding data related to the coefficients from the bit stream and decodes the coding data existing in the header part of the bit stream. The header part of the bit stream illustrated in Fig. 5 is first decoded, and the pixel depth information and the PCM pixel depth information are reproduced to be output to a subsequent stage according to the present embodiment. The coding data in units of block of picture data, that is, the predictive coding pixel information and the PCM pixel information are subsequently output to the first decoding unit 103 and the second image decoding and reproduction unit 106. In a case where the decoding target block has been subjected to the predictive coding, the predictive coding pixel information is output to the first decoding unit 103. In a case where the decoding target block has been subjected to the PCM coding, the PCM pixel information is output to the second image decoding and reproduction unit 106.

The first decoding unit 103 decodes the predictive coding pixel information input from the separate decoding unit 102 to reproduce the quantization parameter, the quantization coefficients, and the prediction information. The reproduced quantization parameter and quantization coefficients are output to the inverse quantization and inverse transform unit 104, and the reproduced prediction information is output to the first image reproduction unit 105.

With regard to the block after the predictive coding, the inverse quantization and inverse transform unit 104 performs inverse quantization on the input quantization coefficients by using the reproduced quantization parameter to generate inverse transform coefficients and further performs inverse orthogonal transform to generate the prediction errors. The reproduced prediction errors are input to the first image reproduction unit 105.

The first image reproduction unit 105 generates a prediction image by appropriately referring to the frame memory 107 on the basis of the prediction information input from the first decoding unit 103. The image data is reproduced from the prediction image and the prediction errors input from the inverse quantization and inverse transform unit 104 to be input to the frame memory 107 for storage. The stored image data is used for a reference at the time of a prediction.

The second image decoding and reproduction unit 106 generates reproduction image data from the PCM pixel information by using the pixel depth information and the PCM pixel depth information input from the separate decoding unit 102 to be input to the frame memory 107 for storage.

The generation processing for the reproduction image data in the second image decoding and reproduction unit 106 according to the present embodiment will be specifically described. Fig. 2 illustrates a detailed block diagram thereof. The pixel depth information is input to a terminal 201. The PCM pixel depth information is input to a terminal 202. The coding data of the PCM pixel information is input to a terminal 203. A value of the pixel depth information is denoted by ds, and a value of the PCM pixel depth information is denoted by dp herein. A bit depth difference calculation unit 204 is configured to obtain a difference between the pixel depth information value ds and the PCM pixel depth information value dp. This difference value is denoted as dd. A correction value calculation unit 205 is configured to calculate an offset on the basis of the difference value dd calculated by the bit depth difference calculation unit 204. An I_PCM decoding unit 206 is configured to decode the coding data of the PCM pixel information and reproduce a value Pp of the PCM pixel information. A bit shift unit 207 is configured to perform bit shift on the value Pp of the reproduced PCM pixel information by a predetermined number of bits. A pixel value correction unit 208 is configured to correct an output from the bit shift unit 207 on the basis of an output from the correction value calculation unit 205. The corrected pixel value is output from a terminal 209.

The pixel depth information value ds input from the terminal 201 and the PCM pixel depth information value dp input from the terminal 202 are input to the bit depth difference calculation unit 204. The bit depth difference calculation unit 204 obtains the difference value dd on the basis of Expression (1).
dd = ds - dp (1)

The calculated difference value dd is input to the correction value calculation unit 205 and the bit shift unit 207.

The correction value calculation unit 205 calculates an offset value Op from the difference value dd while following Expression (2).
Op = 1 << (dd - 1) (2)

Expression (2) represents that 2 to the power of (dd - 1) is set as the offset value Op.

The calculated offset value Op is input to the pixel value correction unit 208.

In the picture decoding, the coding data after the I_PCM coding is input to the I_PCM decoding unit 206 from the terminal 203. The I_PCM decoding unit 206 decodes the coding data to reproduce the PCM pixel information value Pp. The reproduced PCM pixel information value Pp is input to the bit shift unit 207, and the bit shift is conducted to the left by the difference value dd. The result is input to the pixel value correction unit 208. The pixel value correction unit 208 performs a correction by adding the offset value Op to the value input from the value input from the bit shift unit 207 and outputs the reproduction pixel value Pc from the terminal 209.

The second image decoding and reproduction unit 106 has the configuration illustrated in Fig. 2 according to the present embodiment but is not limited to this. The second image decoding and reproduction unit 106 may be composed of a correction unit configured to perform a computation of Expression (3) directly from the pixel depth information value ds and the PCM pixel depth information value dp with respect to the PCM pixel information value Pp, for example.
Pc = ((Pp << (ds - dp)) + (1 << (ds - dp - 1))) (3)

Expression (3) represents that a sum of a product between Pp and 2 to the power of (ds - dp) and 2 to the power of (ds - dp - 1) is set as Pc.

In a case where the PCM pixel depth information value (dp) is 1 and the pixel depth information value (ds) is 8, for example, the PCM pixel information value (Pp) is 0 or 1. However, with regard to the corresponding reproduction pixel, the reproduction pixel value (Pc) is 64 in a case where the PCM pixel information value (Pp) is 0, and the reproduction pixel value (Pc) is 192 in a case where the PCM pixel information value (Pp) is 1. In a case where the PCM pixel depth information value (dp) is 4 and the pixel depth information value (ds) is 8, for example, the PCM pixel information value (Pp) is a value in a range between 0 and 15, but the corresponding reproduction pixel value (Pc) is in a range between 8 and 248 with increments of 16. With reference to Fig. 1 again, the finally reproduced image data is output to the external part from the terminal 108.

Fig. 3 is a flow chart of an image decoding processing in the image decoding apparatus according to the first exemplary embodiment.

In step S301, the separate decoding unit 102 first separates the information related to the decoding processing and the coding data related to the coefficients from the bit stream and decodes the coding data in the header part to reproduce the pixel depth information and the PCM pixel depth information.

In step S302, the separate decoding unit 102 decodes the information related to the block of the decoding target from the picture data of the bit stream to separate the predictive coding pixel information and the PCM pixel information. PCM coding block determination information indicating whether or not the decoding target block has been subjected to the PCM coding is generated from the information related to the decoded block of the decoding target.

In step S303, the image decoding apparatus determines whether or not the decoding target block has been subjected to the PCM coding on the basis of the PCM coding block determination information generated in step S302. In a case where the decoding target block has been subjected to the PCM coding, the flow progresses to step S307. In a case where the decoding target block has not been subjected to the PCM coding, that is, in a case where the decoding target block has been subjected to the predictive coding, the flow progresses to step S304.

In step S304, the first decoding unit 103 decodes the predictive coding pixel information separated in step S302 and reproduces the reproduced quantization parameter, the quantization coefficients, and the prediction information.

In step S305, the inverse quantization and inverse transform unit 104 performs the inverse quantization by the reproduced quantization parameter with respect to the quantization coefficients in units of block to obtain transform coefficients and further perform inverse orthogonal transform to reproduce prediction errors.

In step S306, the first image reproduction unit 105 reproduces a predictive image on the basis of the prediction information generated in step S304. The image data is reproduced from the reproduced predictive image and the prediction errors generated in step S305.

On the other hand, in step S307, the I_PCM decoding unit 206 of the second image decoding and reproduction unit 106 decodes the coding data of the PCM pixel information to reproduce the PCM pixel information. In step S308, the second image decoding and reproduction unit 106 uses the pixel depth information and the PCM pixel depth information reproduced in step S301 to reproduce the image data from the PCM pixel information reproduced in step S307. The reproduction processing in this step is also similarly represented as Expression (3) described above.

In step S309, the image decoding apparatus determines whether or not the decoding for all the blocks is ended. If the decoding is ended, the decoding processing is ended. If the decoding is not ended, the next block is set as a target, and the flow returns to step S302.

With the above-described configuration and operation, it is possible to reproduce the image while suppressing the degradation of the pixels processed with the PCM coding by appropriately correcting and reproducing the pixels in the block with the PCM coding particularly in step S308.

The decoding of the bit stream illustrated in Fig. 5 has been illustrated according to the present embodiment, but the configuration of decoding the bit stream is not limited to this.

The second image decoding and reproduction unit 106 and the reproduction method for the pixels in the block with the PCM coding in step S307 have been described as an example by using Expression (3), but the reproduction method is not limited. Any system of adding the offset value corresponding to the PCM pixel depth information and the pixel depth information to any PCM pixel may be adopted.

With respect to the PCM pixel information value Pp, for example, computation of the following Expression (4) or (5) may also be conducted from the pixel depth information value ds and the PCM pixel depth information value dp.

In a case where Pp < (1 << (dp - 1)) is satisfied, the following computation is conducted.
Pc = ((Pp << (ds - dp))) (4)

In the other cases, the following computation is conducted.
Pc = ((Pp << (ds - dp)) + ((1 << (ds - dp)) - 1)) (5)

Expression (4) herein represents that a product of Pp and 2 to the power of (ds - dp) is set as Pc, and Expression (5) represents that a sum of a product of Pp and 2 to the power of (ds - dp) and a difference between 2 to the power of (ds - dp) and 1 is set as Pc.

The correction value calculation unit 205 may calculate ((1 << (ds - dp)) - 1) as an offset, and the pixel value correction unit 208 may determine whether the addition is made on the basis of the input bit shift result.

In a case where the PCM pixel depth information value (dp) is 1 and the pixel depth information value (ds) is 8, for example, the PCM pixel information value (Pp) is 0 or 1. In this case, with regard to the corresponding reproduction pixel, the reproduction pixel value (Pc) is 0 in a case where the PCM pixel information value (Pp) is 0, and the reproduction pixel value (Pc) is 255 in a case where the PCM pixel information value (Pp) is 1.

In a case where the PCM pixel depth information value (dp) is 4 and the pixel depth information value (ds) is 8, for example, the PCM pixel information value is a value in a range between 0 and 15. In a case where the PCM pixel information value is a value in a range between 0 and 7, since a value at the part added in a latter part of Expression (4) is 0, the corresponding reproduction pixel value (Pc) is 0 to 112 with increments of 16. On the other hand, in a case where the PCM pixel information value is a value in a range between 8 and 15, since a value at the part added in the latter part of Expression (4) is 15, the corresponding reproduction pixel value (Pc) is 143 to 255 with increments of 16. In this example, it is possible to reproduce the image while a dynamic range of the pixel that has been subjected to the PCM coding is maintained. Furthermore, according to the present embodiment, since a median of the pixel that has been subjected to the PCM coding after the correction is matched with a median of the pixel of the output image, the image quality degradation caused by the bit shift computation may also be suppressed.

The example in which the correction value takes a linear value has been described according to the present embodiment, but the configuration is not limited to this. A non-linear correction value may also be used. The case in which the coding data of the PCM pixel information is coded has been described according to the present embodiment, but in a case where the unprocessed value is included, the I_PCM decoding unit 206 may be omitted, and step S307 may be omitted.

Second exemplary embodiment

Fig. 6 is a block diagram of a configuration of an image decoding apparatus according to a second exemplary embodiment. In Fig. 6, components realizing functions similar to those of Fig. 1 according to the first exemplary embodiment are assigned with the same reference symbols, and a description thereof will be omitted.

A description will be given while the decoding of the bit stream illustrated in Fig. 5 is taken as an example according to the present embodiment, but the pixel depth information, the PCM pixel depth information, and the PCM pixel information in the bit stream are independent in terms of luminance and chrominance. Luminance pixel depth information and chrominance pixel depth information as well as luminance PCM pixel depth information and chrominance PCM pixel depth information exist in the header part, and luminance PCM pixel information and chrominance PCM pixel information exist in the picture data part. The bit stream to be decoded is of course not limited to this.

A separate decoding unit 302 separates the information related to the decoding processing and the coding data related to the coefficient from the bit stream similarly as in the separate decoding unit 102 of Fig. 1 and also decodes coding data existing in the header part of the bit stream. A difference from the separate decoding unit 102 of Fig. 1 resides in that the PCM pixel depth information and the PCM pixel information which are independently prepared for the luminance and the chrominance are output.

A luminance second image decoding and reproduction unit 310 reproduces the luminance PCM pixel information from the luminance reproduction image data for output by using the luminance pixel depth information and the luminance PCM pixel depth information output from the separate decoding unit 302.

A chrominance second image decoding and reproduction unit 311 reproduces the chrominance reproduction image data from the chrominance PCM pixel information for output by using the chrominance pixel depth information and the chrominance PCM pixel depth information output from the separate decoding unit 302.

A decoding operation for the image in the above-described image decoding apparatus will be described below.

The separate decoding unit 302 separates the information related to the decoding processing, the coding data related to the coefficients from the bit stream, and the coding data related to the pixel information and decodes the coding data existing in the header part of the bit stream. The header part of the bit stream illustrated in Fig. 5 is first decoded according to the present embodiment, and the luminance pixel depth information and the chrominance depth information included in the pixel depth information and the luminance PCM pixel depth information and the chrominance PCM pixel depth information included in the PCM pixel depth information are reproduced to be output to a subsequent stage. Specifically, the luminance pixel depth information and the luminance PCM pixel depth information are output to the luminance second image decoding and reproduction unit 310, and the chrominance pixel depth information and the chrominance PCM pixel depth information are output to the chrominance second image decoding and reproduction unit 311. The predictive coding pixel information in units of block of the picture data as well as the luminance PCM pixel information and the chrominance PCM pixel information included in the PCM pixel information are subsequently output to the first decoding unit 103, the luminance second image decoding and reproduction unit 310, and the chrominance second image decoding and reproduction unit 311. More specifically, in a case where the decoding target block has been subjected to the predictive coding, the separate decoding unit 302 outputs the predictive coding pixel information to the first decoding unit 103. In a case where the decoding target block has been subjected to the PCM coding, the luminance PCM pixel information is output to the luminance second image decoding and reproduction unit 310, and the chrominance PCM pixel information is output to the chrominance second image decoding and reproduction unit 311.

The luminance second image decoding and reproduction unit 310 generates the luminance reproduction image data from the luminance PCM pixel information by using the luminance pixel depth information and the luminance PCM pixel depth information input from the separate decoding unit 302 to be input to the frame memory 107 for storage. The generation processing for the luminance reproduction image data in the luminance second image decoding and reproduction unit 310 according to the present embodiment is illustrated in Fig. 2 similarly as in the second image decoding and reproduction unit 106 according to the first exemplary embodiment except that the target is only the luminance pixel, and therefore a description there of will be omitted.

The chrominance second image decoding and reproduction unit 311 generates the chrominance reproduction image data from the chrominance PCM pixel information by using the chrominance pixel depth information and the chrominance PCM pixel depth information input from the separate decoding unit 302 to be input to the frame memory 107 for storage. The generation processing for the chrominance reproduction image data in the chrominance second image decoding and reproduction unit 311 according to the present embodiment is illustrated in Fig. 2 similarly as in the second image decoding and reproduction unit 106 according to the first exemplary embodiment except that the target is only the chrominance pixel, and therefore a description there of will be omitted.

Fig. 7 is a flow chart of image decoding processing in the image decoding apparatus according to the second exemplary embodiment. Components realizing similar functions to those of Fig. 3 according to the first exemplary embodiment are assigned with the same reference symbols, and therefore a description there of will be omitted.

In step S701, the separate decoding unit 302 separates the information related to the decoding processing and the coding data related to the coefficients from the bit stream. The coding data in the header part is then decoded, and the luminance pixel depth information, the chrominance pixel depth information, the luminance PCM pixel depth information, and the chrominance PCM pixel depth information are reproduced.

In step S707, the I_PCM decoding unit 206 of the luminance second image decoding and reproduction unit 310 decodes the luminance coding data of the PCM pixel information to reproduce the luminance PCM pixel information.

In step S708, the luminance second image decoding and reproduction unit 310 reproduces luminance image data from the luminance PCM pixel information from reproduced in step S707 by using the luminance pixel depth information and the luminance PCM pixel depth information reproduced in step S701.

In step S709, the I_PCM decoding unit 206 of the chrominance second image decoding and reproduction unit 311 decodes the chrominance coding data of the PCM pixel information to reproduce the chrominance PCM pixel information.

In step S710, the chrominance second image decoding and reproduction unit 311 reproduces chrominance image data from the chrominance PCM pixel information reproduced in step S709 by using the chrominance pixel depth information and the chrominance PCM pixel depth information reproduced in step S701.

With the above-described configuration and operation, it is possible to reproduce the image while suppressing the degradation of the pixel and performing optimal corrections with respect to the luminance and the chrominance by appropriately correcting and reproducing the pixel in the block that has been subjected to the PCM coding of the luminance and the chrominance particularly in steps S708 and S710.

The luminance second image decoding and reproduction unit 310 and the chrominance second image decoding and reproduction unit 311 as well as steps S708 and S710 are independently prepared for the luminance and the chrominance according to the present embodiment, but these may perform the same processing or may also perform independent processings. The processing represented in Expression (3) described above may be conducted for the luminance and the chrominance, for example. A combination of techniques may also be adopted in which while the processing represented in Expression (4) or (5) is conducted for the luminance, the technique in related art is conducted for the chrominance.

The case has been described in which the pixel depth information and the PCM pixel depth information are different in terms of the luminance and the chrominance, but the configuration is not limited to this. Contents of the processings for the luminance and the chrominance from the same pixel depth information and PCM pixel depth information may be varied as described above.

Processings appropriate to the respective characteristics may be conducted. Processing of maintaining a dynamic range of the reproduction pixel represented as in Expression (4) or (5) may be conducted for the luminance, for example, and reproduction processing including a correction to reproduce a value close to a median may be conducted for the chrominance. An example will be described in which the chrominance PCM pixel depth information value (dp) is 1 and the chrominance pixel depth information value (ds) is 8 for the chrominance. With regard to the corresponding reproduction pixel, the chrominance reproduction pixel value (Pc) is 96 in a case where the chrominance PCM pixel information value (Pp) is 0, and the chrominance reproduction pixel value (Pc) is 160 in a case where the chrominance PCM pixel information value (Pp) is 1. In this case, a value is closer to 128 that is the median than the luminance at 64 or 192. Such a non-linear correction may of course be conducted as described above.

The reproduction processing is independently conducted for the luminance and the chrominance according to the present embodiment, but the reproduction processing may also be conducted independently for each color space. The reproduction processing represented in Expression (4) or (5) may be conducted for a Y color space component, for example, the reproduction processing represented in Expression (3) may be conducted for a U color space component, and the reproduction processing in related art may be conducted for a V color space component.

Third exemplary embodiment

The embodiments have been described while the respective processing units illustrated in Fig. 1 and Fig. 6 are composed by using hardware. However, the processings conducted in the respective processing units illustrated in Fig. 1 and Fig. 6 may be realized by using a computer program.

Fig. 4 is a block diagram of a hardware configuration example of a computer applicable to the image display apparatus according to the respective embodiments of the present invention.

A CPU 401 controls the entire computer by using a computer program or data stored in a RAM 402 or a ROM 403 and also executes the above-described respective processings that are set to be conducted by the image processing apparatus according to the above-described respective embodiments. The CPU 401 thus functions as the respective processing units illustrated in Fig. 1 and Fig. 6.

The RAM 402 includes an area for temporarily storing a computer program or data loaded from an external storage apparatus 406, data externally obtained from an interface (I/F) 407, and the like. The RAM 402 further includes a work area used when the CPU 401 executes the various processings. Therefore, the RAM 402 may be allocated as a frame memory, for example, or the RAM 402 may appropriately provide other various areas.

The ROM 403 stores setting data of the computer, a boot program, and the like. An operation unit 404 is composed of a key board, a mouse, or the like. While a user of the computer operates the operation unit 404, various instructions may be input to the CPU 401. A display unit 405 displays a processing result by the CPU 401. The display unit 405 is composed, for example, of a liquid crystal display.

The external storage apparatus 406 is a large-capacity information storage apparatus represented by a hard disk drive. The external storage apparatus 406 saves the computer program for the CPU 401 to realize an operating system (OS) or the functions of the respective units illustrated in Fig. 1 and Fig. 6. The external storage apparatus 406 may further save respective pieces of image data as processing targets.

The computer program or the data saved in the external storage apparatus 406 is appropriately loaded to the RAM 402 while following a control by the CPU 401 to be the processing target by the CPU 401. A network such as a LAN or the internet and other devices such as a projection apparatus and a display apparatus may be connected to the I/F 407. The computer may obtain and transmit various pieces of information via the I/F 407. A bus 408 connects the above-described respective units one another.

The CPU 401 mainly performs the control on the operations composed of the above-described configurations through the operations described above in the flow charts.

Other Embodiments

Aspects of the present invention can also be realized by a computer of a system or apparatus (or devices such as a CPU or MPU) that reads out and executes a program recorded on a memory device to perform the functions of the above-described embodiment(s), and by a method, the steps of which are performed by a computer of a system or apparatus by, for example, reading out and executing a program recorded on a memory device to perform the functions of the above-described embodiment(s). For this purpose, the program is provided to the computer for example via a network or from a recording medium of various types serving as the memory device (e.g., computer-readable medium).

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No. 2012-092214, filed April 13, 2012, which is hereby incorporated by reference herein in its entirety.

Claims

An image decoding method of decoding a bit stream and reproducing an image, the image decoding method comprising:
decoding blocks coded in a first coding mode in which a prediction is conducted; and
decoding blocks coded in a second coding mode in which the prediction is not conducted,
wherein the decoding the blocks coded in the first coding mode includes conducting a first reconstruction of generating a first reproduction image from reproduced prediction errors and results of the prediction, and
wherein the decoding the blocks coded in the second coding mode includes conducting a second reconstruction of generating a second reproduction image by, in a case where a bit depth of pixel information of the blocks coded in the second coding mode is smaller than a bit depth of an output image, reproducing output pixel tentative values through a bit shift of the pixel information on the basis of a difference between the bit depth of the output image and the bit depth of the pixel information and correcting the output pixel tentative values on the basis of the difference between the bit depths to calculate output pixel values.
The image decoding method according to Claim 1, wherein the conducting the second reconstruction includes calculating an offset on the basis of the difference between the bit depths and adding the offset to the output pixel tentative value to calculate the output pixel value.
The image decoding method according to Claim 1, wherein the conducting the second reconstruction includes calculating the output pixel value from an output bit depth, the bit depth of the block coded in the second coding mode, and the pixel information of the block coded in the second coding mode.
An image decoding apparatus that decodes a bit stream and reproduces an image, the image decoding apparatus comprising:
a first decoding unit configured to decode blocks coded in a first coding mode in which a prediction is conducted; and
a second decoding unit configured to decode blocks coded in a second coding mode in which the prediction is not conducted,
wherein the first decoding unit includes a first reconstruction unit configured to generate a first reproduction image from reproduced prediction errors and results of the prediction, and
wherein the second decoding unit includes a second reconstruction unit configured to generate a second reproduction image by, in a case where a bit depth of pixel information of the block coded in the second coding mode is smaller than a bit depth of an output image, reproducing output pixel tentative values through a bit shift of the pixel information on the basis of a difference between the bit depth of the output image and the bit depth of the pixel information and correcting the output pixel tentative values on the basis of the difference between the bit depths to calculate output pixel values.
The image decoding apparatus according to Claim 4, wherein the second reconstruction unit calculates an offset on the basis of the difference between the bit depths and adds the offset to the output pixel tentative value to calculate the output pixel value.
The image decoding apparatus according to Claim 4, wherein the second reconstruction unit calculates the output pixel value from an output bit depth, the bit depth of the block coded in the second coding mode, and the pixel information of the block coded in the second coding mode.
A computer-readable program executed by a computer to cause the computer to function as the image decoding apparatus according to Claim 4.