T 0210/21 10-04-2024

1. The appeal is admissible.

2. Interpretation of document D1

2.1 The inventive step assessment in the decision under appeal hinges on document D1 disclosing a pointer in the header of a dependent slice identifying an independent slice (see the second paragraph on page 3, the first paragraph after the claim wording on page 5 and the third and fourth paragraphs on page 6 of the decision under appeal).

This point has been contested by the appellant in first-instance and appeal proceedings. The appellant alleged that the examining division had erroneously interpreted the disclosure of document D1 (see the section entitled "5 Reply to arguments of the appellant" on page 5 of the decision under appeal and the paragraph starting with "Briefly speaking" on page 3 of the statement of grounds of appeal).

2.2 Document D1 identifies a number of issues that could occur when using the slice header signalling of dependent slices defined in the text specification draft for wavefront parallel processing (WPP) available at that time.

In WPP, rows of coding tree blocks are processed in parallel. Processing of a coding tree block requires the left, top-left, top, and top-right coding tree blocks to be available for predictions to operate correctly. Thus, a shift of at least two coding tree blocks is enforced between consecutive rows of coding tree blocks processed in parallel.

2.2.1 A first issue is that when using WPP, decoding of a dependent slice cannot start if the preceding slice has not been completely decoded. This is because, in order to start its decoding, a dependent slice needs to obtain slice header syntax elements of the preceding slice containing the coding tree block in raster scan order previous to the first coding tree block of the dependent slice (see the second bullet point in the abstract and section 2.2). However, since the last coding tree block of a slice is not available until the slice is completely decoded, the slice cannot be used to determine whether its last coding tree block is the one previous to the first coding tree block of the dependent slice.

2.2.2 A second issue with WPP arises when a complete dependent slice containing a row of coding tree blocks is lost. If the decoder does not detect this loss, it may assume that the previously received slice is the lost slice. Decoding the subsequent slice under this assumption would result in an erroneous slice reconstruction that could propagate until the last slice in the picture (see the third bullet point in the abstract and section 2.3).

2.2.3 To solve these issues, document D1 proposes signalling the slice address of the reference slice in the header of a dependent slice so that the reference slice can be easily identified and its loss quickly detected (see section 3, point 2). For this purpose, the syntax element "ref_slice_address" specifies the address of "the slice whom the current slice depends on" (see section 3, first paragraph on page 4).

2.3 The examining division and the appellant differed in their interpretation of the phrases "the reference slice" and "the slice whom the current slice depends on".

2.3.1 According to the appellant, the syntax element "ref_slice_address" in a dependent slice segment (dependent slice) referred to the slice address of the immediate predecessor slice segment (slice) rather than to the slice address of the independent slice segment (independent slice) to which a current slice segment belonged (see the paragraph beginning with "Briefly speaking" on page 3 of the statement of grounds of appeal).

2.3.2 The examining division considered that the syntax element "ref_slice_address" in the header of a dependent slice pointed to the independent slice that contained the dependent slice (see, for example, the third and fourth paragraphs on page 6 of the decision under appeal).

2.4 The board agrees with the appellant that D1 does not disclose a pointer to an independent slice in the header of a dependent slice.

2.4.1 Terms used in patent documents should be given their normal meaning in the relevant art, unless the description gives them a special meaning (see Case Law of the Boards of Appeal of the European Patent Office, 10th edition, 2022, I.C.4.1). The board considers that the same principle applies to technical input documents to JCT-VC standardisation meetings.

2.4.2 According to document D1, "the reference slice of [a] dependent slice is the preceding slice containing the coding tree block for which the coding tree block address is ctbAddrTStoRS[ctbAddrRStoTS[slice_address] ? 1]" (see the second bullet point in the abstract). This expression roughly translates into the reference slice of a dependent slice being the one that contains the coding tree block previous to the first coding tree block in the dependent slice in raster scan order. Thus, in the context of D1, a reference slice is the previous slice.

2.4.3 The scenario shown in section 2.3 of document D1 confirms this interpretation. It illustrates a picture coded with WPP where each row of coding tree blocks except the first one is coded as a dependent slice. The dependent slice depends on the previously received slice. The reference slice of the fourth slice is the third slice. Both slices are dependent slices.

2.4.4 In view of points 2.4.2 and 2.4.3 above, the board considers that, in the context of D1, the phrases "the reference slice" and "the slice whom the current slice depends on" identify the previous slice. Thus, the syntax element "ref_slice_address", which specifies the address of the slice which the current slice depends on, points to the previous slice.

As an aside, the board notes that, according to the examining division's interpretation of D1, this document would not solve any of the issues identified in points 2.2.1 and 2.2.2 above. Indeed, by signalling the address of the independent slice in the syntax element "ref_slice_address", it would still not be possible either to identify the reference (previous) slice before it had been fully decoded, or to detect a preceding lost slice.

3. Inventive step (Article 56 EPC)

3.1 In the decision under appeal, the examining division considered that D1 disclosed a syntax element in the header of a dependent slice pointing to the independent slice that contained the dependent slice.

3.2 In view of section 2. above, the board holds that the examining division based its inventive step assessment on an erroneous interpretation of document D1. Since document D1 does not disclose a signalling method with a syntax element in the header of a dependent slice pointing to the independent slice that contained the dependent slice, the person skilled in the art adapting the method known from document D1 would not have arrived at the claimed signal syntax.

3.3 Consequently, the examining division's conclusion that the subject-matter of claim 1 lacked inventive step in view of the disclosure of document D1 in combination with the disclosure of document D2 and the common general knowledge of the person skilled in the art was not correct.

4. Remittal (Article 111(1) EPC, Article 11 RPBA)

4.1 Under Article 111(1) EPC, the board, in deciding upon the appeal, may exercise any power within the competence of the department which was responsible for the appealed decision or remit the case to that department for further prosecution.

Article 12(2) RPBA expressly states that the primary object of the appeal proceedings is a judicial review of the appealed decision.

Article 11 RPBA provides that the board should not remit a case for further prosecution unless special reasons present themselves for doing so.

4.2 The examining division's erroneous interpretation of document D1 calls into question the relevance of this document to the assessment of the patentability of the claimed subject-matter and the completeness of the search for fundamental concepts on which the claimed invention is based (referencing of independent data elements from dependent data elements). Furthermore, the relevance of the remaining prior-art documents on file to the subject-matter of the independent claims was not discussed in examination proceedings.

Thus, if the board were itself to decide on the substance of the case and not remit the case to the department of first instance, the board would have to for the first time carry out a full examination of the application with regard to patentability requirements. This is primarily the task of the examining division (see decision G 10/93 of the Enlarged Board of Appeal, OJ EPO 1995, 172, point 4 of the Reasons). As the misinterpretation of document D1 may well have brought the search to a premature end, the board might even have to determine whether an additional search was necessary.

4.3 These circumstances constitute a special reason within the meaning of Article 11 RPBA justifying a remittal to the department of first instance for further prosecution.

4.4 The board has therefore decided to exercise its discretion under Article 111(1) EPC by remitting the case to the department of first instance for further prosecution.