TECHNICAL FIELD

The present invention relates to an image processing device and method, and specifically relates to an image processing device and method which enable prediction efficiency to be improved.

BACKGROUND ART

In recent years, there have come into widespread use devices which subject an image to compression encoding by employing an encoding format for handling image information as digital signals, and taking advantage of redundancy peculiar to the image information with transmission and storage of high effective information taken as an object at that time to compress the image by orthogonal transform such as discrete cosine transform or the like and motion compensation. Examples of this encoding method include MPEG (Moving Picture Experts Group) and so forth.

In particular, MPEG2 (ISO/IEC 13818-2) is defined as a general-purpose image encoding format, and is a standard encompassing both of interlaced scanning images and sequential-scanning images, and standard resolution images and high definition images. For example, MPEG2 has widely been employed now by broad range of applications for professional usage and for consumer usage. By employing the MPEG2 compression format, a code amount (bit rate) of 4 through 8 Mbps is allocated in the event of an interlaced scanning image of standard resolution having 720×480 pixels, for example. Also, by employing the MPEG2 compression format, a code amount (bit rate) of 18 through 22 Mbps is allocated in the event of an interlaced scanning image of high resolution having 1920×1088 pixels, for example. Thus, a high compression rate and excellent image quality can be realized.

With MPEG2, high image quality encoding adapted to broadcasting usage is principally taken as a object, but a lower code amount (bit rate) than the code amount of MPEG1, i.e., an encoding format having a higher compression rate is not handled. According to spread of personal digital assistants, it has been expected that needs for such an encoding format will be increased from now on, and in response to this, standardization of the MPEG4 encoding format has been performed. With regard to an image encoding format, the specification thereof was confirmed as international standard as ISO/IEC 14496-2 in December in 1998.

Further, in recent years, standardization of a standard serving as H.26L (ITU-T Q6/16 VCEG) has progressed with image encoding, originally intended for television conference usage. With H.26L, it has been known that as compared to a conventional encoding format such as MPEG2 or MPEG4, though greater computation amount is requested for encoding and decoding thereof, higher encoding efficiency is realized. Also, currently, as part of activity of MPEG4, standardization for also taking advantage of a function that is not supported by H.26L with this H.26L taken as a base, to realize higher encoding efficiency, has been performed as Joint Model of Enhanced-Compression Video Coding. As a schedule of standardization, H.264 and MPEG-4 Part 10 (Advanced Video Coding, hereafter referred to as H.264/AVC) become an international standard in March, 2003.

Further, as an extension thereof, standardization of FRExt (Fidelity Range Extension) including a coding tool necessary for business use such as RGB, 4:2:2, or 4:4:4, 8×8DCT and quantization matrix stipulated by MPEG-2 has been completed in February, 2005. Thus, H.264/AVC has become a encoding format capable of suitably expressing even film noise included in movies, and has been employed for wide ranging applications such as Blu-Ray Disc (registered trademark) and so forth.

However, nowadays, needs for further high-compression encoding have been increased, such as intending to compress an image having around 4000×2000 pixels, which is quadruple of a high-vision image. Alternatively, needs for further high-compression encoding have been increased, such as intending to distribute a high-vision image within an environment with limited transmission capacity like the Internet. Therefore, with the above-mentioned VCEG (=Video Coding Expert Group) under the control of ITU-T, studies relating to improvement of encoding efficiency have continuously been performed.

Now, one factor that can be given why the H.264/AVC format realizes high encoding efficiency as compared to the conventional MPEG2 format or the like is employing an intra prediction method.

With the intra prediction method, the intra prediction modes of nine kinds of 4×4 pixel and 8×8 pixel block units, and four kinds of 16×16 pixel macro block units are determined regarding luminance signals. The intra prediction modes of four kinds of 8×8 pixel block units are determined regarding color difference signals. The intra prediction modes for color difference signals may be set independently from the intra prediction modes for luminance signals.

There are particular patterns for each intra prediction mode regarding how residual following such intra prediction is manifested.

As a method to eliminate such redundancy and further raise encoding efficiency, NPL 1 proposes the following method.

That is to say, intra image encoding processing is performed by normal H.264/AVC format using training signals in offline processing beforehand, orthogonal transform such as Karhunen-Loeve transform or the like is performed for each intra prediction mode as to each block, and optimal transform coefficients are calculated.

Then, in the actual encoding processing, processing using orthogonal transform coefficients optimized for each mode by the aforementioned Karhunen-Loeve transform are used instead of the orthogonal transform stipulated by the H.264/AVC format.

Also, NPL 2 proposes a method of combining the aforementioned intra prediction with inter prediction.

That is to say, with NPL 2, difference information is generated as to motion vector information obtained in inter prediction not only for a current block but also for neighboring pixel values around the current block. Performing intra prediction between the difference information relating to the current block, and the difference information relating to neighboring pixels, generated in this way, generates second order difference information. The generated second order difference information is then subjected to orthogonal transform and quantization, and output downstream along with a compressed image.

Thus, encoding efficiency is further improved.

Also, as described above, the macro block size is 16×16 pixels with the H.264/AVC format. However, a macro block size of 16×16 pixels is not optimal for large image frames such as UHD (Ultra High Definition; 4000×2000 pixels) which will be handled by next-generation encoding methods.

Accordingly, NPL 3 and so forth propose enlarging the macro block size to a size of 32×32 pixels, for example.

CITATION LIST

Non Patent Literature

NPL 1: “Improved Intra Coding”, VCEG-AF15, ITU-Telecommunications Standardization Sector STUDY GROUP Question 6 Video coding Experts Group (VCEG), 20-21 Apr. 2007NPL 2: “Second Order Prediction (SOP) in P Slice”, Sijia Chen, Jinpeng Wang, Shangwen Li and, Lu Yu, VCEG-AD09, ITU-Telecommunications Standardization Sector STUDY GROUP Question 6 Video coding Experts Group (VCEG), 16-18 Jul. 2008NPL 3: “Video Coding Using Extended Block Sizes”, VCEG-AD09, ITU-Telecommunications Standardization Sector STUDY GROUP Question 16—Contribution123, January 2009

SUMMARY OF INVENTION

Technical Problem

Now, with the H.264/AVC format, low-pass filter processing of pixel values of neighboring pixels is performed before performing intra prediction in increments of blocks of 8×8 pixels describe above. Thus, noise included in the neighboring pixels is removed, and correlation is raised, so higher encoding efficiency can be realized.

However, regardless the fact that the degree of included noise differs according to the input images, quantization parameter values, intra prediction modes, and so forth, the low-pass filter for removing the noise has been fixed with the H.264/AVC format. That is to say, this low-pass filter has not been optimal in accordance with input images, quantization parameter values, intra prediction modes, and so forth.

Also, with the H.264/AVC format, the noise removal of pixel values of neighboring pixels described above is only performed with the intra prediction mode in increments of blocks of 8×8 pixels, and has not been applied for other modes.

The present invention has been made in light of this situation, and realizes noise removal in accordance with images and bit rates, thereby improving prediction efficiency.

Solution to Problem

An image processing device according to a first aspect of the present invention includes: decoding means configured to decode an image of a current block which is to be the object of decoding processing; filter setting means configured to set, in accordance with the current block, a coefficient to be used for filtering processing to which neighboring pixels of the current block are to be subjected to, used for intra prediction of the current block, in accordance with an encoding parameter; and intra prediction means configured to subject the neighboring pixels to the filtering processing using the coefficient set by the filter setting means, and performing intra prediction of the current block.

The encoding parameter may include a mode of intra prediction of the current block, or a quantization parameter of the current block; the decoding means may decode the mode of intra prediction of the current block or the quantization parameter of the current block; and the filter setting means may set the coefficient in accordance with the mode of intra prediction decoded by the decoding means, or the quantization parameter decoded by the decoding means.

The image processing device may further include: filter coefficient storage means configured to store the coefficient; wherein the coefficient is calculated so as to obtain, with a learning image, the smallest residual between a learning block which is the object of encoding processing, and a prediction image obtained by performing intra prediction for the learning block corresponding to a mode of intra prediction of the learning block or a quantization parameter of the learning block, and is stored in the filter coefficient storage means; and wherein the filter setting means set, as the coefficient, that from the coefficients stored in the filter coefficient storage means which corresponds to the mode of intra prediction of the current block, or the quantization parameter of the current block.

The filter coefficient storage means may hold the coefficient as an n-bit (wherein n is an integer) value in accordance with a register length of a processor.

The decoding means may decode the coefficient, which has been calculated at an encoding side using the neighboring pixels prior to being subjected to the filtering processing such that the residual as to a prediction image obtained by intra prediction being performed regarding the current block is smallest, and which has been set corresponding to the current block, and to the mode of intra prediction of the current block or the quantization parameter of the current block; and the filter setting means may set, as the coefficient, that from the coefficients decoded by the decoding means which corresponds to the mode of intra prediction of the current block, or the quantization parameter of the current block.

The coefficient may be configured of a filter coefficient and offset value.

The filter coefficient may be configured of three taps.

The filter coefficient may have symmetry centered on a coefficient corresponding to zero-phase.

The decoding means may decode the mode of intra prediction of the current block; and the filter setting means may take, of modes of intra prediction, a vertical mode or horizontal mode as a first class, and other modes as a second class, and, in the event that the mode of intra prediction of the current block belongs to the first class, set the coefficient corresponding to the first class, and in the event that the mode of intra prediction of the current block which has been decoded belongs to the second class, set the coefficient corresponding to the second class.

The image processing device may further include: receiving means configured to receive flag information indicating whether or not to perform the filtering processing as to the neighboring pixels; wherein the filter setting means set whether or not to perform the filtering processing as to the neighboring pixels, based on flag information received by the receiving means.

The receiving means may receive the flag information in increments of macro blocks; and the filter setting means may set whether or not to perform the filter processing as to the neighboring pixels, in increments of macro blocks, based on flag information received by the receiving means.

The receiving means may receive the flag information in increments of blocks; and the filter setting means may set whether or not to perform the filter processing as to the neighboring pixels, in increments of blocks, based on flag information received by the receiving means.

An image processing method according to the first aspect of the present invention includes the steps of: an image processing device performing decoding of an image of a current block which is to be the object of decoding processing; setting of, in accordance with the current block, a coefficient to be used for filtering processing to which neighboring pixels of the current block are to be subjected to, used for intra prediction of the current block, in accordance with an encoding parameter; and subjecting the neighboring pixels to the filtering processing using the coefficient that has been set, and performing intra prediction of the current block.

An image processing device according to a second aspect of the present invention includes: filter setting means configured to set a coefficient to be used for filtering processing to which neighboring pixels of a current block which is to be the object of decoding processing are to be subjected to, used for intra prediction of the current block, in accordance with an encoding parameter; intra prediction means configured to subject the neighboring pixels to the filtering processing using the coefficient set by the filter setting means, and performing intra prediction of the current block; and encoding means configured to encode an image of the current block.

The encoding parameter may include a mode of intra prediction of the current block, or a quantization parameter of the current block; and the filter setting means may set the coefficient in accordance with the mode of intra prediction of the current block, or the quantization parameter of the current block; and the encoding means may encode the corresponding mode of intra prediction of the current block or quantization parameter of the current block.

The image processing device may further include: filter coefficient storage means configured to store the coefficient; wherein the coefficient is calculated so as to obtain, with a learning image, the smallest residual between a learning block which is the object of encoding processing, and a prediction image obtained by performing intra prediction for the learning block corresponding to a mode of intra prediction of the learning block or a quantization parameter of the learning block, and is stored in the filter coefficient storage means; and wherein the filter setting means set, as the coefficient, that from the coefficients stored in the filter coefficient storage means which corresponds to the mode of intra prediction of the current block, or the quantization parameter of the current block.

The image processing device may further include: filter coefficient calculating means configured to calculate the coefficient such that the residual between the current block, and a prediction image obtained by intra prediction being performed regarding the current block, using the neighboring pixels prior to being subjected to the filtering processing in accordance with the mode of intra prediction of the current block or the quantization parameter of the current block is smallest; wherein the filter setting means set, as the coefficient, that from the coefficients calculated by the filter coefficient calculating means which corresponds to the mode of intra prediction of the current block, or the quantization parameter of the current block; and wherein the encoding means further encode the coefficient.

The coefficient may be configured of a filter coefficient and offset value.

The filter setting means may set whether or not to perform the filtering processing as to the neighboring pixels; and the encoding means may encode flag information indicating whether or not to perform the filtering processing set by the filter setting means.

An image processing method according to the second aspect of the present invention includes the steps of: an image processing device performing setting of a coefficient to be used for filtering processing to which neighboring pixels of a current block which is to be the object of decoding processing are to be subjected to, used for intra prediction of the current block, in accordance with an encoding parameter; subjecting the neighboring pixels to the filtering processing using the coefficient that has been set, and performing intra prediction of the current block; and encoding an image of the current block.

With the first aspect of the present invention, an image of a current block which is to be the object of decoding processing is decoded, a coefficient is set, which is to be used for filtering processing to which neighboring pixels of the current block are to be subjected to which are used for intra prediction of the current block, in accordance with an encoding parameter. The neighboring pixels are then subjected to the filtering processing using the coefficient that has been set, and intra prediction of the current block is performed.

With the second aspect of the present invention, an a coefficient is set, to be used for filtering processing to which neighboring pixels of a current block which is to be the object of decoding processing are to be subjected to which are used for intra prediction of the current block, in accordance with an encoding parameter, the neighboring pixels are subjected to the filtering processing using the coefficient that has been set, intra prediction of the current block is performed, and an image of the current block is encoded.

Note that the above-described image processing devices may be stand-alone devices, or may be internal blocks making up one image encoding device or image decoding device.

Advantageous Effects of Invention

According to the first invention, images can be decoded. Also, according to the second invention, noise removal can be performed in accordance with the image and the bit rate.

According to the second invention, images can be encoded. Also, according to the first invention, noise removal can be performed in accordance with the image and the bit rate.

