T 0709/16 21-10-2020

1. The appeal is admissible.

2. The invention

2.1 The application relates to the compression and coding of videos. Conventionally, a signal is compressed by eliminating redundancies and by reducing the set of output values via a process called quantisation.

2.2 There are different ways of eliminating redundancies in a video:

One possibility is to predict the content of a block of pixels using neighbouring pixel values in the same image ("intra" prediction) or using pixel values of a corresponding block in a reference image ("inter" prediction, a.k.a. "motion compensation"). The prediction is then subtracted from the block to generate a prediction residual. According to MPEG standards, a picture to be compressed is divided into macroblocks of size 16x16. Each macroblock can be further divided into blocks on which intra or inter prediction is performed.

An additional possibility for eliminating redundancies is to transform the prediction residual into a frequency space where the energy of the signal is shared among a smaller number of coefficients. This transform may be an orthogonal transformation.

2.3 Conventionally, coefficients obtained after orthogonal transformation are quantised. For this, it is known to use a weighting matrix that changes the quantisation steps on a per-frequency component basis (application as filed, page 19, lines 4 to 9).

2.4 The background art mentioned in the application is an existing picture coding apparatus and an existing picture decoding apparatus (page 5, line 26 to page 7, line 32) in which the size of the orthogonal transformation is fixed (page 8, lines 10 to 20).

2.5 To accommodate different content, it is desirable to use an adaptive size (page 8, lines 20 to 29).

2.6 The claims of the main request and of auxiliary request I relate to a picture coding method and a picture decoding method in which the size of the orthogonal transformation is set to (i) 8x8 pixels in a motion compensation block of size 16x16, 16x8, 8x16 or 8x8 pixels, and (ii) 4x4 pixels in a motion compensation block of size 8x4, 4x8 or 4x4 pixels. Transform coefficients are quantised using a weighting matrix corresponding to the selected orthogonal transformation size. The weighting matrix is inserted in the coded stream.

3. Main request, interpretation of claim 1

3.1 The board finds that the interpretation adopted by the appellant (see point X.(a) above) contradicts the passages on page 14, lines 5 to 7 and page 16, lines 10 to 12 of the application as filed. Indeed, these passages teach that the finest level in the coding structure at which an orthogonal transformation size is selected is the macroblock level.

3.2 The board also finds that the passages cited by the appellant do not disclose that 8x8 motion compensation blocks within a macroblock are independently partitioned into motion compensation blocks of size 8x4, 4x8 or 4x4 pixels. In particular, they do not indicate that the partitioning of a macroblock complies with the standard H.264/MPEG-4 AVC.

3.3 The passage from page 15, line 7 to page 16, line 9, when read in combination with the passage on page 14, lines 5 to 7, can also be understood as meaning that all motion compensation blocks within a macroblock have the same size and that this size is used to determine the orthogonal transformation size on a per-macroblock basis.

3.4 The passage on page 9, lines 26 to 29 relates to an embodiment in which an additional size information is transmitted within the coded stream. This embodiment is to be distinguished from the selection of an orthogonal transformation size based on the motion compensation block size.

3.5 In view of the above, the board holds that, on proper interpretation within the context of the application, claim 1 of the main request does not necessarily imply that the selection between a first and a second orthogonal transformation size is performed independently for the various motion compensation blocks within a macroblock. It also covers the situation where all motion compensation blocks within a macroblock have the same size and only one selection of an orthogonal transformation size is made for the macroblock.

4. Main request, inventive step (Article 56 EPC 1973)

4.1 According to Article 56 EPC 1973, an invention is to be considered as involving an inventive step if, having regard to the state of the art, it is not obvious to a person skilled in the art.

4.2 The following assessment of whether the invention claimed in claim 1 of the main request involves an inventive step follows the established "problem and solution approach" (Case Law of the Boards of Appeal of the European Patent Office ("Case Law"), 9th edition 2019, I.D.2).

4.3 It is common ground that document D5 may be considered the closest prior art in the context of this approach (see point 1.1 of the impugned decision and point 2.1 of the statement of grounds of appeal).

4.4 It is also common ground that document D5 discloses a picture coding method in which the size of the orthogonal transformation is set to (i) 8x8 pixels in a motion compensation block of size 16x16, 16x8, 8x16 or 8x8 pixels, (ii) 8x4, 4x8 or 4x4 pixels in a motion compensation block of size 8x4, 4x8 or 4x4 pixels respectively (page 11, section 6.4, page 34, lines 1 to 3; page 128, section 12.1; and page 135, section 12.3.1.3, equations (12-1) and (12-2)). Different weighting matrices are used for quantisation of coefficients obtained with different orthogonal transformation sizes. Equation (8-41) on page 74 specifies the weighting matrix used in quantising a 4x4 transform block (see equation (8-48) on page 75), whereas equations (12-4) and (12-6) on pages 144 and 145 specify the weighting matrices used in quantising 8x8, 8x4 and 4x8 transform blocks.

4.5 It is also common ground that document D5 does not disclose Feature (a) or Feature (b).

4.6 However, the board does not agree that Feature (c) is a further distinguishing feature (see point X.(b)(iii) above). Section 6.4 on page 11 of document D5 discloses that a motion compensation block can have a size of 16x16, 16x8 or 8x16 pixels.

4.7 The board has not been convinced that Feature (b) improves coding efficiency and that Feature (a) and Feature (b) achieve a synergistic effect. The values of the weighting matrix inserted in the coded stream are not limited by claim 1. Thus there is no guarantee that, for a given output image quality, the additional bits needed for signalling these values in the coded stream are compensated for by a reduction in the number of bits necessary to signal the quantized coefficients. In any case, even if the board acknowledged that Feature (b) improved coding efficiency, the resulting coding efficiency obtained by Feature (a) and Feature (b) would merely be the sum of the respective impact of Feature (a) and Feature (b) on coding efficiency.

4.8 It is established case law that, if the features or sets of features of a claim are a mere aggregation of these features or sets of features which are not functionally interdependent, i.e. do not mutually influence each other to achieve a technical success over and above the sum of their respective individual effects, it is to be established whether each set of features is separately obvious in the light of the state of the art (Case Law, I.D.9.2.2).

4.9 Thus, in view of point 4.7, it is to be established whether each of Feature (a) and Feature (b) is separately obvious in the light of the state of the art.

4.10 Feature (a)

4.10.1 In view of point 3.5 above, the board has doubts whether Feature (a) results in less switching between orthogonal transformation sizes and thus whether it achieves the intended simplification of the coding apparatus. However, in the appellant's favour, the following assessment of inventive step is based on the assumption that the selection between a first and a second orthogonal transformation size is performed independently for the various motion compensation blocks within a macroblock, and thus that Feature (a) leads to less switching between orthogonal transformation sizes within a macroblock.

4.10.2 Hence the board formulates the first partial objective technical problem as being how to simplify the coding apparatus of document D5.

4.10.3 The board does not agree with the appellant that the person skilled in the art would not have thought of reducing the number of possible orthogonal transformation sizes. It is obvious to seek simplification in any part of an apparatus. The person skilled in the art of video coding would have sought to simplify any part of the coding apparatus disclosed in document D5, in particular any part related to the orthogonal transformation.

4.10.4 Depending on whether greater simplification or greater flexibility was desired, the person skilled in the art would have used only one of the possible orthogonal transform sizes - for example the 4x4 pixel size (point X.(c) above) - or several of them. The 4x4 and 8x8 pixel sizes are the only sizes representing common denominators among the orthogonal transform sizes used in document D5 (8x8, 8x4, 4x8, 4x4). The person skilled in the art would have correctly foreseen the trade-off between simplification and flexibility achieved by using these two sizes. Hence this solution merely represents one obvious solution among several.

4.10.5 In view of the above, Feature (a) does not contribute to an inventive step.

4.11 Feature (b)

4.11.1 In point 4.9 above, the board came to the conclusion that Feature (b) had to be assessed separately from Feature (a).

4.11.2 The board agrees that Feature (b) increases coding flexibility.

4.11.3 Thus the board formulates the second partial objective technical problem as being how to increase the flexibility of the coding apparatus.

4.11.4 Since the insertion of a weighting matrix in the coded stream is contemplated in the standard MPEG-2 (as recalled in document D7, column 16, lines 28 to 31), the board finds that Feature (b) is obvious in view of the common general knowledge of the person skilled in the art.

4.12 In view of the above, the subject-matter of claim 1 lacks inventive step within the meaning of Article 56 EPC 1973 because it is obvious in view of the disclosure of document D5 combined with the common general knowledge of the person skilled in the art.

5. Auxiliary request I, admittance (Article 13(2) RPBA 2020)

5.1 In the present case, the summons to oral proceedings was notified after the date on which RPBA 2020 entered into force, i.e. 1 January 2020 (Article 24(1) RPBA 2020). Thus, in accordance with Article 25(1) and (3) RPBA 2020, Article 13(2) RPBA 2020 applies to the question of whether to admit the appellant's auxiliary request I, which was filed after the summons to oral proceedings was notified, and it is therefore an amendment within the meaning of Article 13(2) RPBA 2020.

5.2 Article 13(2) RPBA 2020 implements the third level of the convergent approach applicable in appeal proceedings (see document CA/3/19, section VI, Explanatory remarks on Article 13(2), first paragraph, first sentence; see also Supplementary publication 2, OJ EPO 2020). Article 13(2) RPBA 2020 imposes the most stringent limitations on appeal submissions which are made at an advanced stage of the proceedings, namely after expiry of a period set by the board of appeal in a communication under Rule 100(2) EPC or, where no such communication is issued, after notification of a summons to oral proceedings (see document CA/3/19, section VI, Explanatory remarks on Article 13(2), first paragraph, second sentence). Where an amendment is made to a party's appeal case at this advanced stage of the proceedings, Article 13(2) RPBA 2020 provides that it will, in principle, no longer be taken into account unless the party concerned has shown compelling reasons why the circumstances are exceptional. If such circumstances are shown to exist, the board of appeal may, in exercising its discretion, decide to admit an amendment made to the appeal case at this advanced stage of the proceedings (see document CA/3/19, section VI, Explanatory remarks on Article 13(2), third paragraph, last sentence).

5.3 The Explanatory remarks on Article 13(2) RPBA 2020 also contain the following guidance: "At the third level of the convergent approach, the Board may also rely on criteria applicable at the second level of the convergent approach, i.e. as set out in proposed new paragraph 1 of Article 13." (Document CA/3/19, section VI, Explanatory remarks on Article 13(2), fourth paragraph). The board takes the view that, at the third level of the convergent approach, the boards of appeal are free to use or not use the criteria set out in Article 13(1) RPBA 2020 when deciding, in exercising their discretion in accordance with Article 13(2) RPBA 2020, whether to admit an amendment made at this stage of the proceedings (see also decisions T 989/15, point 16.2 of the Reasons, and T 954/17, point 3.10 of the Reasons).

5.4 The board accepts the appellant's argument that the board's comments in point 3.3.2 of its communication under Article 15(1) RPBA 2020 represent exceptional circumstances within the meaning of Article 13(2) RPBA 2020. However, it is still within the board's discretion to admit the request into the appeal proceedings.

5.5 The board finds it appropriate to rely on the criterion of "suitability" set out in Article 13(1) RPBA 2020. Therefore, the board exercises its discretion in view of the suitability of the amendment to resolve the issue of lack of inventive step raised by the board.

According to the appellant, the amendment to the patent application was only meant to clarify that a selection between a first and a second orthogonal transformation size was not made for only a single motion compensation block (see point XI. above).

Since the analysis of inventive step in relation to the main request is already made on this assumption (see point 4.10.1 above), the board finds that the amendment is not suitable to resolve the issue of lack of inventive step raised by the board.

5.6 In view of the above, the board exercised its discretion under Article 13(2) RPBA 2020 and decided not to admit auxiliary request I into the appeal proceedings.

6. Auxiliary request II - request for remittal

Since the board has decided on the allowability of the main request and the admittance of auxiliary request I, remitting the case to the department of first instance for further prosecution under Article 111(1), second sentence, EPC 1973 would have no meaningful purpose. Therefore, the appellant's auxiliary request II cannot be granted.

7. Since none of the appellant's requests is allowable, the appeal is to be dismissed.