Adaptive filtering for scalable video coding

In a scalable video codec, an adaptive Wiener filter with offset aims to minimize the differences between two input pictures or picture regions, and the filter coefficients need to be transmitted to decoder site.

BACKGROUND

This relates generally to scalable video codecs. The scalable video codec may be bit-depth scalable video codec, spatial scalable video codec, temporal scalable video codec, color space scalable video codec, color format scalable video codec, and etc.

Scalable video codecs enable different picture quality levels to be delivered to different customers, depending on what type of service they prefer. Lower quality video services may be less expensive than higher quality video services.

In a bit-depth scalable video coder, a lower bit depth may be called a baseline layer and a higher bit depth may be called an enhancement layer. The greater the bit depth, the better the quality of the video. In a spatial scalable video coder, a lower picture resolution may be called a baseline layer and a higher picture resolution may be called an enhancement layer. The larger the picture resolution, the better the quality of the video. Other scalabilities include spatial scalability, temporal scalability, signal-to-noise ratio (SNR) scalability, color format scalability, color gamut or color space scalability.

In a scalable video codec, an encoder and decoder may be provided as one unit. In some cases, only an encoder may be provided and, in other cases, only a decoder may be provided. The scalable video coder enables the system to operate with at least the baseline layer. Thus, in low cost systems, only the baseline layer may be utilized and, in higher cost, more advanced systems, one or more enhancement layers may be utilized.

It is advantageous to derive the enhancement layer from the baseline layer. To this end, inverse tone mapping may be utilized in bit-depth scalable video coding to increase the bit depth of the baseline layer to the bit depth of the enhancement layer. In some cases, for example, the baseline layer may be 8 bits per pixel and the enhancement may be 10, 12, or higher bits per pixel.

DETAILED DESCRIPTION

Referring toFIG. 1, a scalable video codec includes an encoder10that communicates over a video transmission or a video storage14with a decoder12.FIG. 1shows an encoder from one codec with a decoder from another codec.

As an example, a network computer may communicate over the network with another computer. Each computer may have a codec which includes both an encoder and a decoder so that information may be encoded at one node, transmitted over the network to the other node, which then decodes the encoded information.

The codec shown inFIG. 1is a scalable video codec (SVC). This means that it is capable of encoding and/or decoding information with different qualities, e.g., different bit depths, different picture sizes and etc. Video sources16and26may be connected to the encoder10. For bit-depth scalability, the video source16may use N-bit video data, while the video source26may provide M-bit video data, where the bit depth M is greater than the bit depth N. For spatial scalability, the video source16may use smaller picture size video data, while the video source26may provide bigger picture size video data. In other embodiments, more than two sources with more than two bit depths or two picture sizes may be provided.

In each case, the information from a video source is provided to an encoder. In the case of the video source16, of lower bit depth, the information is provided to a baseline encoder18. In the case of the video source26, of higher bit depth, an enhancement layer encoder28is utilized.

The baseline encoder ofFIG. 1may be consistent with the H.264 (advanced video codec (AVC) and MPEG-4 Part 10) or HEVC (high efficient video codec), compression standard, for example. The H.264 standard has been prepared by the Joint Video Team (JVT), which includes ITU-T SG16 Q.6, also known as VCEG (Video Coding Expert Group), and of the ISO-IEC JTC1/SC29/WG11 (2003), known as MPEG (Motion Picture Expert Group). The HEVC standard is been preparing by the Joint Collaborative Team on Video Coding (JCTVC), which also includes VCEG and MPEG, and will be finalized by January 2013. H.264 and HEVC are designed for applications in the area of digital TV broadcast, direct broadcast satellite video, digital subscriber line video, interactive storage media, multimedia messaging, digital terrestrial TV broadcast, and remote video surveillance, to mention a few examples.

While one embodiment may be consistent with HEVC video coding, the present invention is not so limited. Instead, embodiments may be used in a variety of video compression systems including H.264/AVC, MPEG-2 (ISO/IEC13818-1 (2000) MPEG-2 available from International Organization for Standardization, Geneva, Switzerland) and VC1 (SMPTE 421 M (2006) available from SMPTE White Plains, N.Y. 10601).

Adaptive filtering may be achieved by a Wiener filter in one embodiment. A Wiener filter is a filter that achieves the least mean square error among the source signal and the predicted signal modeled through the random noise. “Adaptive filtering” means that filtering is content dependent or based on an analysis of pixel intensities in a portion of a picture, a picture as a whole, or a plurality of successive pictures. For example, the type of video information that is received, be it graphics or stream view video, results in different taps in the Wiener filter for different types of video. Thus, adaptive filter taps are the result of an examination of the intensity of each pixel in a given picture portion, picture, or series of pictures.

The encoder provides information over the video transmission or video storage14for use by a decoder. The information that may be provided may include the baseline (BL) layer video stream, the lower layer picture process information (e.g., inverse tone mapping (ITM) information for bit-depth scalability or picture up-scale information for spatial scalability), the filter taps from the adaptive filtering24, and the enhancement layer (EL) video stream. Some of this information may be included in a packet header. For example, the inverse tone mapping (ITM) or picture up-scale information and the filter tap information may be provided in an appropriate header in packetized data transmission.

In a video codec, an adaptive Wiener filter aims to minimize the differences between two input pictures or picture regions, and the filter coefficients may be transmitted to the decoder site. For SVC enhancement layer coding, let Q(x,y) denote the value of an enhancement layer input pixel at position (x,y), and P(x,y) denotes the value of the processed lower layer reconstructed pre-filtering pixel at position (x,y). An adaptive Wiener filter with offset is performed on P(x,y) as equation (12) below to get the post-filter pixel value P′(x,y), where, Cm,ndenotes the adaptive filtering coefficients, and Offset denotes the offset value.
P′(x,y)=Σm=−NnN′P(x+m,y+n)Cm,n+Offset  (12)
M0, M1, N0, N1are parameters to control the number of Wiener filter taps. With different settings of M0, M1, N0, N1, the filter may be a symmetric filter or asymmetric filter, a 1-D filter or 2D filter, as examples.

The coefficients Cm,nand offset value Offset may be adaptively generated at the encoder side and then may be coded into bitstreams for the enhancement layer decoding. One method to generate Cm,nand Offset values is to minimize the sum of squared distortions between Q(x, y) and P′(x, y). A Cm,nand/or the offset value may be forced to be zero, and then only the remaining filter parameters need to be derived by the encoder and then be sent to decoder. If the offset is forced to be zero, the filter equation (12) will be changed to equation (13). If Wiener filter is not used, the filter equation in (12) will be changed to equation (14).
P′(x,y)=Σm=−M0N′P(x+m,y+n)Cm,n(13)
P′(x,y)=P(x,y)+Offset  (14)

FIG. 2shows an example decoding flow of a three-layer SVC bitstream, i.e., one base layer and two enhancement layers. The scalability may be spatial scalability, bit-depth scalability of some other scalability. The blocks52, “Inter-layer Adaptive Filtering L1” and “Inter-layer Adaptive Filtering L2” are added into the SVC decoding flow to improve the inter-layer predictions. The inter-layer adaptive filters are applied on the processed lower layer picture to improve its quality. The three other adaptive filtering blocks, i.e., “Adaptive Filtering L0”, “Adaptive Filtering L1” and “Adaptive Filtering L2” in the decoding flow are standard adaptive filtering blocks in one embodiment, as used in HEVC/H.265 coding standard, to improve the quality of the output video. The “Lower Layer Picture Process” may use frame-up scaling for spatial scalability, tone mapping for bit-depth scalability, or passing through without any processing.

InFIG. 2the layer zero bitstream is provided to entropy decoding40. The entropy decoded bitstream is provided to inverse quantization and transform42. This is provided to a mixer44that receives an input via switch56from either an intra prediction unit38or motion compensation unit36. In the case of the layer zero bitstream, the switch is connected to the intra prediction unit38. After mixing the data from the intra prediction unit38and the inverse quantization and transform unit42, the stream is deblock filtered at deblock filtering46. Finally adaptive filtering L0 occurs at48to output a layer zero output video.

The layer zero output video is also provided to the next layer, layer one also labeled enhancement layer decoding flow32. Particularly the layer zero output video is provided for lower layer picture process50in layer32. Then the video is provided to the inter-layer adaptive filtering L1 block52and finally to the inter-layer prediction block54. From here it is conveyed via the switch56to the mixer44. The output from the layer32, called layer one output video, is also provided to the lower layer picture process50in the layer2or enhancement layer decoding flow34. Otherwise the sequence is the same as described in connection with the layer one. Ultimately, layer two video is output as indicated.

FIG. 3shows the inter-layer predictions with adaptive filtering for enhancement layer LX at encode size. The inter-layer adaptive filtering60aims to minimize the differences between the enhancement layer input picture Q(x, y) and the processed lower layer output picture P(x,y)50in one embodiment. The output filtered picture P′(x,y) is then used for inter-layer prediction54.

In one embodiment, we can apply one filter on all pixels in the picture, and the encoder can decide turning on or turning off the filter and then send a flag to decoder to indicate the decision result. Considering that one filter may lack adaptation on some local areas of the picture, local adaptive filtering may be applied to achieve better coding efficiency.

In local adaptive filtering, the picture may be divided into multiple regions and then different filtering schemes may be applied to different regions. In one embodiment, only one filter is applied to the whole picture, and the encoder can decide for each region whether it should be filtered or not and then the encoder may send flags to the decoder to indicate the decision results. In another embodiment, multiple filters are applied to the whole picture, and the encoder can decide for each region whether it should be filtered or not and if it should be filtered, which filter (i.e. filter table index) should be used to filter this region and then send the decision results to decoder.

There are different criteria to partition a picture into multiple regions. In some embodiments, we can partition the picture into different regions according to pixel positions, e.g., uniformly dividing the whole picture into M×N regions. In some other embodiments, we can partition the picture into different regions by categorizing pixels into different classes according to pixel features, e.g., pixel values or pixel edge and gradient information, and one class of pixels is regarded as one region. In some other embodiments, we can partition the picture into different regions by dividing the picture into multiple small blocks and then categorizing the blocks into different classes according to the block features, e.g., average pixel value of the block or average edge and gradient information of the block, then one class of blocks is regarded as one region.

In some embodiments, the inter-layer adaptive filtering of an enhancement layer may re-use the region filter parameter, e.g., filter on/off flag and filter table index, of lower layers, and then those re-used information is not needed to be transmitted for this enhancement layer. In some other embodiments, the encoder can adaptively decide to re-use the lower layer adaptive filtering parameters or not, and, with re-use, to use the filter parameters of which lower layer, and then send the decision results to decoder.

SVC inter-layer prediction may be improved by applying the adaptive filter on processed lower layer reconstructed pictures. Here the lower layer reconstructed picture processing includes, for example, frame up-scaling for spatial scalability, tone mapping for bit-depth scalability, or passing through without any processing. Adaptive filtering aims to reduce the differences/distortion between the input pixels of an enhancement layer and the processed reconstructed pixels of its lower layer.

An adaptive Wiener filter with offset may act as the adaptive filter to improve the SVC inter-layer prediction of an enhancement layer coding. The Wiener filter coefficient and the offset value may be adaptively generated at the encoder side and then encoded and transmitted to decoder. In some embodiments, the offset value may be forced to zero, and only the Wiener filter coefficients need to be generated at the encoder side and then sent to decoder. In some embodiments, we only apply the offset value for filtering without applying the Wiener filter, then, only the offset value needs to be generated at encoder side and then be sent to decoder. In some embodiments, part of the Wiener filter coefficients may be forced to be zero to save the transmission bandwidth, and then only the remaining coefficients need to be generated at encoder side and then be sent to decoder.

The adaptive filter may be applied on the whole picture, i.e., all pixels in the picture use the same filter. The encoder may decide whether the whole picture should be filtered or not, and then transmit a flag to decoder to indicate the decision result. The picture may be partitioned into different regions, and then the adaptive filter may be applied on each region. Then encoder decides which regions should be filtered and then sends flags to decoder to indicate the decision results.

The picture may be partitioned into multiple regions and then different adaptive filters may be applied to different regions. The encoder can derive the filter parameters for each region and then encode and send the parameters to the decoder for decoding. Also, for each region, the encoder can decide whether it should be filtered or not, and then send flags to decoder to indicate the decision results.

Predictive coding of the enhancement layer filter coefficients may be used. The filter coefficient may be intra predicted, i.e., by predicting the value of one filter coefficient from the values of other coefficients of the same filter, or be inter predicted, i.e., by predicting the value of one filter coefficient from the coefficients of other filters. The other filters may be other filters of the same enhancement layer if multiple filters are applied for this enhancement layer picture, or the filters used for lower layers of the picture, or the filters used for other coded pictures.

Multiple predictive coding methods for filter coefficients may be used. The encoder may decide which predictive coding method should be used and then sends a flag to decoder to indicate the decision result.

The picture may be partitioned into different regions according to pixel positions, e.g., uniformly dividing the whole picture into M×N regions. The picture may be partitioned into different regions by categorizing pixels into different classes according to some other pixel features, e.g., pixel values or pixel edge and gradient information, and one class of pixels may be regarded as one region.

The picture may be partitioned into different regions by dividing the picture into multiple small blocks and then categorizing the blocks into different classes according to the block features, e.g., average pixel value of the block or average edge and gradient information of the block. Then one class of blocks is regarded as one region. If an adaptive filter is used for lower layer coding, the region filtering flags of the adaptive filters of lower layers for an enhancement layer adaptive filtering may be re-used. Then it is unnecessary to transmit independent region filtering flags for this enhancement layer, saving some transmission bandwidth in some embodiments. Here the lower layer adaptive filters may be the filters for improving the inter-layer prediction of lower enhancement layer, or the filters for improving the output video quality of lower layer. In some other embodiments, the encoder can adaptively decide to re-use the lower layer adaptive filtering parameters or not, and if re-use is chosen, to use the filter parameters of which lower layer, and then send the decision results to decoder.

FIG. 4illustrates an embodiment of a system700. In embodiments, system700may be a media system although system700is not limited to this context. For example, system700may be incorporated into a personal computer (PC), laptop computer, ultra-laptop computer, tablet, touch pad, portable computer, handheld computer, palmtop computer, personal digital assistant (PDA), cellular telephone, combination cellular telephone/PDA, television, smart device (e.g., smart phone, smart tablet or smart television), mobile internet device (MID), messaging device, data communication device, and so forth.

In embodiments, system700comprises a platform702coupled to a display720. Platform702may receive content from a content device such as content services device(s)730or content delivery device(s)740or other similar content sources. A navigation controller750comprising one or more navigation features may be used to interact with, for example, platform702and/or display720. Each of these components is described in more detail below.

In addition, the platform702may include an operating system770. An interface to the processor772may interface the operating system and the processor710.

Firmware790may be provided to implement functions such as the boot sequence. An update module to enable the firmware to be updated from outside the platform702may be provided. For example the update module may include code to determine whether the attempt to update is authentic and to identify the latest update of the firmware790to facilitate the determination of when updates are needed.

In some embodiments, the platform702may be powered by an external power supply. In some cases, the platform702may also include an internal battery780which acts as a power source in embodiments that do not adapt to external power supply or in embodiments that allow either battery sourced power or external sourced power.

Processor710may be implemented as Complex Instruction Set Computer (CISC) or Reduced Instruction Set Computer (RISC) processors, x86 instruction set compatible processors, multi-core, or any other microprocessor or central processing unit (CPU). In embodiments, processor710may comprise dual-core processor(s), dual-core mobile processor(s), and so forth.

Graphics subsystem715may perform processing of images such as still or video for display. Graphics subsystem715may be a graphics processing unit (GPU) or a visual processing unit (VPU), for example. An analog or digital interface may be used to communicatively couple graphics subsystem715and display720. For example, the interface may be any of a High-Definition Multimedia Interface, DisplayPort, wireless HDMI, and/or wireless HD compliant techniques. Graphics subsystem715could be integrated into processor710or chipset705. Graphics subsystem715could be a stand-alone card communicatively coupled to chipset705.

In embodiments, display720may comprise any television type monitor or display. Display720may comprise, for example, a computer display screen, touch screen display, video monitor, television-like device, and/or a television. Display720may be digital and/or analog. In embodiments, display720may be a holographic display. Also, display720may be a transparent surface that may receive a visual projection. Such projections may convey various forms of information, images, and/or objects. For example, such projections may be a visual overlay for a mobile augmented reality (MAR) application. Under the control of one or more software applications716, platform702may display user interface722on display720.

In embodiments, content services device(s)730may be hosted by any national, international and/or independent service and thus accessible to platform702via the Internet, for example. Content services device(s)730may be coupled to platform702and/or to display720. Platform702and/or content services device(s)730may be coupled to a network760to communicate (e.g., send and/or receive) media information to and from network760. Content delivery device(s)740also may be coupled to platform702and/or to display720.

Movements of the navigation features of controller750may be echoed on a display (e.g., display720) by movements of a pointer, cursor, focus ring, or other visual indicators displayed on the display. For example, under the control of software applications716, the navigation features located on navigation controller750may be mapped to virtual navigation features displayed on user interface722, for example. In embodiments, controller750may not be a separate component but integrated into platform702and/or display720. Embodiments, however, are not limited to the elements or in the context shown or described herein.

In embodiments, drivers (not shown) may comprise technology to enable users to instantly turn on and off platform702like a television with the touch of a button after initial boot-up, when enabled, for example. Program logic may allow platform702to stream content to media adaptors or other content services device(s)730or content delivery device(s)740when the platform is turned “off.” In addition, chip set705may comprise hardware and/or software support for 5.1 surround sound audio and/or high definition 7.1 surround sound audio, for example. Drivers may include a graphics driver for integrated graphics platforms. In embodiments, the graphics driver may comprise a peripheral component interconnect (PCI) Express graphics card.

In various embodiments, any one or more of the components shown in system700may be integrated. For example, platform702and content services device(s)730may be integrated, or platform702and content delivery device(s)740may be integrated, or platform702, content services device(s)730, and content delivery device(s)740may be integrated, for example. In various embodiments, platform702and display720may be an integrated unit. Display720and content service device(s)730may be integrated, or display720and content delivery device(s)740may be integrated, for example. These examples are not meant to limit the invention.

As described above, system700may be embodied in varying physical styles or form factors.FIG. 4illustrates embodiments of a small form factor device800in which system700may be embodied. In embodiments, for example, device800may be implemented as a mobile computing device having wireless capabilities. A mobile computing device may refer to any device having a processing system and a mobile power source or supply, such as one or more batteries, for example.

As shown inFIG. 5, device800may comprise a housing802, a display804, an input/output (I/O) device806, and an antenna808. Device800also may comprise navigation features812. Display804may comprise any suitable display unit for displaying information appropriate for a mobile computing device. I/O device806may comprise any suitable I/O device for entering information into a mobile computing device. Examples for I/O device806may include an alphanumeric keyboard, a numeric keypad, a touch pad, input keys, buttons, switches, rocker switches, microphones, speakers, voice recognition device and software, and so forth. Information also may be entered into device800by way of microphone. Such information may be digitized by a voice recognition device. The embodiments are not limited in this context.

One or more aspects of at least one embodiment, such as those shown inFIGS. 2 and 3may be implemented by representative instructions stored on a non-transitory machine-readable medium which represents various logic within the processor, which when read by a machine causes the machine to fabricate logic to perform the techniques described herein. Such representations, known as “IP cores” may be stored on a tangible, non-transitory machine readable medium and supplied to various customers or manufacturing facilities to load into the fabrication machines that actually make the logic or processor.

The graphics processing techniques described herein may be implemented in various hardware architectures. For example, graphics functionality may be integrated within a chipset. Alternatively, a discrete graphics processor may be used. As still another embodiment, the graphics functions may be implemented by a general purpose processor, including a multicore processor.

The following clauses and/or examples pertain to further embodiments:

One example embodiment may be a method comprising: using an adaptive Wiener filter with offset for video decoding. The method may include applying the adaptive Wiener filter with offset on processed lower layer reconstructed pictures to generate reference pictures for inter-layer predictions. The method may include only applying the adaptive Wiener filter on processed lower layer reconstructed pictures. The method may include only applying the offset on processed lower layer reconstructed pictures. The method may include receiving the filter coefficients and offsets from an encoder. The method may include using the same filter for all pixels in a picture. The method may include adaptively applying the adaptive Wiener filter with offset to each of a plurality of picture regions. The method may include deciding for each region whether to filter the region. The method may include applying predictive coding to enhancement layer filter coefficients. The method may include applying multiple predictive coding for filter coefficients. The method may include partitioning the picture into different regions according to pixel position. The method may include categorizing pixels into classes based on pixel features.

Another example embodiment may be a machine readable medium comprising a plurality of instructions and, in response to being executed on a computing device, causing the computing device to carry out the above-described method.

One example embodiment may be an apparatus comprising: an encoder; and a decoder, coupled to said encoder, with an adaptive Wiener filter with offset. The apparatus may include an operating system, a battery, firmware and a module to update said firmware. The apparatus may include said adaptive Wiener filter to generate reference pictures for interlayer predictions. The apparatus may only apply the adaptive Wiener filter on processed lower layer reconstructed pictures. The apparatus may include said encoder to pass filter coefficients and offsets to said decoder.