As part of an ongoing series examining the patent holders and pools erroneously designating patents as essential, we highlight U.S. Patent 9,674,556 titled “Methods and apparatus for in-loop de-artifact filtering.” This patent is owned by InterDigital VC Holdings, Inc. InterDigital has designated the ’556 patent as essential to the AV1 standard as a part of SISVEL’s AV1 Patent Pool. See AV1 Patent List, AV1 Family AV1-056, available at https://www.sisvel.com/images/documents/Video-Coding-Platform/PatentList_AV1.pdf.

InterDigital’s ’556 patent should not be considered to be essential to the AV1 standard. The ’556 patent is directed to in-loop artifact filtering, and in particular, two filters for successively performing in-loop filtering. The claims of the ’556 patent require (1) “a deblocking filter for performing a first pass to reduce blocking artifacts” and (2) “an adaptive sparse de-noising filter for performing a second pass to reduce noise.” ’556 patent, claim 1.

The AV1 standard uses a de-ringing filter called CDEF as its second filter, not the ’556 patent’s claimed “de-noising filter.” In detail, the AV1 standard employs a distinct process known as the CDEF (constrained directional enhancement filter) process. According to the AV1 standard, the “purpose of the CDEF is to perform deringing….” See AV1, § 7.15 (emphasis added). Contemporaneous research confirms the CDEF works to reduce ringing artifacts. See Midtskogen et al., “The AV1 Constrained Directional Enhancement Filter (CDEF),” arXiv:1602.05975 [cs.MM], Feb. 18, 2016, p. 1, available at https://doi.org/10.48550/arXiv.1602.05975.

Although InterDigital cites the CDEF provisions of the AV1 standard as part of its claims for essentiality, the applicant expressly disclaimed de-ringing filters from the scope of its claims. The ’556 Patent explicitly distinguishes between de-ringing filters (e.g., CDEF) and its claimed “de-noising” filters, listing them as separate filtering options: “At least one of the filters includes, for example, a deblocking filter, a de-ringing filter, a de-noising filter…” ’556 patent, 10:13–16. The difference was confirmed by the applicant during prosecution of the ’556 patent’s parent application, U.S. Patent Application No. 12/312,386, in which the applicant stated that an applied reference’s “deringing filtering does not disclose or suggest a sparse de-noising filter for performing a second pass to reduce noise,” which is similarly included in the ’556 Patent’s claims. See Prosecution History of U.S. Patent Application 12/312,386, Response to Office Action filed June 3, 2014, p. 10 (italics in original).

Moreover, AV1 standard’s use of (1) a deblocking filter followed by (2) de-ringing filter was already well known in the art prior to the ’556 Patent. For example, U.S. Patent 7,738,563 to Pelc, filed over two years prior to the ’556 Patent’s earliest priority date, disclosed a “filter 430 [that] applied [1] deblocking filtering operations and then [2] de-ringing filtering operations.” Pelc ‘563, 5:49-52. Similarly, U.S. Patent 8,537,903 to Lim, filed over a year prior to the ’556 Patent’s earliest priority date, disclosed a decoding system with “[1] a de-blocking system configured to receive decoded video data and decoding information and remove blocking artifacts from the decoded video data, and [2] a de-ringing system configured to remove ringing artifacts from the de-blocked video data.” Lim ‘903, Abstract. Again, this is similar to the operations described in the AV1 standard and distinct from a second-stage “adaptive sparse de-noising filter” in the ’556 Patent.

Thus, the ’556 Patent does not appear to be essential to the AV1 standard even though it has been declared essential and actively licensed as being so. The public would benefit from appropriate scrutiny of patent pools that allegedly cover critical technical standards.

The ’556 Patent is related to U.S. Patent 9,277,243, which InterDigital has also declared essential, but whose non-essentiality is reviewed in this post, https://www.unifiedpatents.com/insights/2023/6/15/interdigital-sisvels-av1-pool-us-9227243.