TECHNIQUE FOR BIT-ACCURATE COMFORT
NOISE ADDITION
CROSS-REFERENCE TO RELATED
APPLICATIONS
[0001] This application claims priority under 35 U.S.C. 119(e) to U.S. Provisional Patent Application Ser. No. 60/511,026, filed on Oct. 14, 2003, the teachings of which are incorporated herein.
TECHNICAL FIELD
[0002] This invention relates to a technique for adding comfort noise to hide compression artifacts.
BACKGROUND ART
[0003] The decoding of a video stream compressed at low bit rate often yields visible artifacts noticeable to a viewer. Blockiness and structured noise patterns are common artifacts that arise when using block-based compression techniques. The human visual system has a greater sensitivity to certain types of artifacts, and thus, such artifacts appear more noticeable and objectionable than others. The addition of random noise to the decoded stream can reduce the noticeability of such compression artifacts, but large frameto-frame differences created by adding random noise can itself produce artifacts that appear noticeable and objectionable.
[0004] The addition of a dither signal can reduce human sensitivity to image artifacts, for example to hide contouring and blocking artifacts. One prior art technique has proposed adding a random noise dither that is based on film grain to an image to disguise block effects. The rationale for adding such random noise is that random error is more forgiving than structured or correlated error. Other prior art techniques have proposed adding a dither signal to a video stream to hide compression artifacts. One past technique has proposed adding a random noise dither in the video encoding and decoding process in the in loop deblocking filter for the ITU/ISO H.264 video coding standard, commonly known as the JVT coding standard. The amount of dither to be added depends on the position of a pixel with respect to a block edge. Another prior technique has proposed adding that random noise subsequent to video decoding (i.e., adding noise as a "post process"), for use as comfort noise. The amount of noise added depends on the quantization parameter and on the amount of noise added to spatially neighboring pixels. The term "comfort noise" comes from the use of noise in audio compression to indicate noise pattern generated at the receiver end to avoid total silence that is uncomfortable to a listener.
[0005] Past comfort noise addition techniques, while effective, have not afforded a desired level of control over the addition of comfort noise, as well as the level of noise to be added.
BRIEF SUMMARY OF THE INVENTION
[0006] Briefly, in accordance with a preferred embodiment of the present principles, there is provided a technique for reducing artifacts in a video image. The method commences by the receipt of supplemental information that accompanies the video image. The supplemental information includes at least one parameter that specifies an attribute of comfort
noise for addition to the video image. Temporally correlated comfort noise is generated and is then added to the image in accordance with the at least one parameter in the supplemental information.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 depicts an apparatus in accordance with the present principles for generating comfort noise in connection with processing of the image block; and
[0008] FIG. 2 depicts an apparatus for use with the apparatus of FIG. 1 for adding comfort noise on a pixel-by-pixel basis.
DETAILED DESCRIPTION
[0009] In accordance with the present principles, the addition of comfort noise to an image serves to hide compression artifacts. To facilitate comfort noise addition in accordance with the present principles, supplemental information accompanying a video image contains at least one parameter that specifies an attribute regarding comfort noise. Typically, the supplemental information includes parameters that function to turn the comfort noise on and off, as well as to indicate the level of noise to add, based on the expected level of compression artifacts.
[0010] In the illustrated embodiment, the video image typically undergoes compression in accordance with the H.264 video compression standard. Accordingly, the supplemental information containing the at least one comfort noise parameter is carried by a registered user data Supplemental Enhancement Information (SEI) message.
Comfort Noise SEI Message
[0011] The use of a registered user data SEI message serves to indicate the use of comfort noise. This message applies to all pictures that follow it until an IDR picture or a new comfort noise or film grain SEI message arrives. Comfort noise SEI messages can only precede I pictures, and only one comfort noise SEI message can precede a particular I picture. I pictures are indicated by slice_type equal to 7, or by nal_ref_idc equal to 5. Table 1 below lists the SEI message elements related to comfort noise:
TABLE 1
user_data registered itu_t_t35( payloadSize ) { C Descriptor
itu_t_t3 5 country co de 5 b (8)
itu_t_t35_payload_byte 5 b(8)
comfort noise flag 5 u(l)
if (comfort noise flag == 1) {
comfort noise_qp offset idc 5 ue(v)
comfort noise_qp_weight offset idc 5 ue(v)
}
}
comfort noise flag equal to 1 indicates that comfort noise addition is
used.
comfort noise flag equal to 0 indicates that comfort noise addition is not
used.
comfort noise qp offset idc indicates the quantization parameter offset
used in the calculation of the additive comfort noise level, and may range in value from -51 to 52.
comfort noise qp weight offset idc indicates a quantization parameter
weight offset used in the calculation of the additive comfort noise level, and may range in value from -6 to 7.
