From Technical Features to Technical Effect — T 1385/25

In the assessment of inventive step, it is common to argue that a distinguishing feature produces a particular technical effect and that the objective technical problem should be formulated accordingly.

But when can a technical effect actually be attributed to the technical features of the claimed invention?

The EPO Board of Appeal’s decision T 1385/25 of 2 October 2026 provides an interesting example.

1. The technical background

The case concerned the partitioning of transform blocks (TBs) in image coding and decoding.

For the 4:2:2 colour format, chroma is sampled at half the horizontal resolution of luma, while the vertical resolution remains the same. One aspect of the application was to determine a maximum width and a maximum height of a chroma transform block separately, rather than using a single maximum transform size.

Starting from D1 as the closest prior art, the Board found that D1 did not disclose determining the maximum width and maximum height of a chroma transform block based on the maximum size of a corresponding luma transform block and the colour format, or determining the width and height of the transform block based on those respective maxima.

The next question was therefore: what technical effect did these distinguishing features achieve?

The appellant argued that they could mitigate “the delay in pipeline processing in an image coding system” and that the objective technical problem should be formulated accordingly. The appellant also relied on the fact that this technical effect and the corresponding problem were identified in the description.

2. Technical effect and the claimed technical features

The Board was not convinced that the alleged effect was achieved across the whole scope of the claimed invention.

In discussing the objective technical problem, the Board referred to G 2/21:

“The technical problem must be derived from effects directly and causally related to the technical features of the claimed invention.”

The Board then stated:

“It follows that a technical effect is only acceptable if all the features contributing to it are explicitly or implicitly specified in the claim.”

In other words, the fact that a technical effect is described in the application does not, by itself, mean that the effect can be relied upon when formulating the objective technical problem.

The question is whether the alleged effect is directly and causally related to the technical features of the claimed invention, and whether that effect is achieved across the whole scope of the claim.

3. What was missing from claim 1?

The description linked the reduction in pipeline-processing delay to more specific technical conditions. For illustration, the relevant reasoning can be simplified as follows:

separate maximum width and height → splitting the chroma CU into TUs so as to correspond to the TUs of the luma CU → encoding or decoding the chroma block immediately after the corresponding luma block → reduced pipeline-processing delay

The Board observed, however, that claim 1 did not specify any pipeline-processing features, “let alone features that could contribute to mitigating the delay in a specific pipeline implementation.” In particular, neither the corresponding TU partitioning nor the immediate processing of the chroma block after the corresponding luma block was derivable from the wording of claim 1.

The Board therefore concluded that, even assuming that the claimed method was implemented in a pipeline-processing architecture, the alleged reduction in delay could not be considered achieved across the whole scope of claim 1.

Importantly, this does not mean that the technical effect of reducing pipeline-processing delay had to be recited as such in the claim. The problem was that conditions contributing to that effect were not specified, explicitly or implicitly, in claim 1.

4. A different effect and a different objective technical problem

Once the alleged reduction in pipeline-processing delay was not retained as an effect achieved across the scope of claim 1, the Board considered what effect could instead be attributed to the claimed features.

In the absence of features relating to pipeline processing, the Board considered the technical effect of using a maximum transform size to be the splitting of a CU into TUs. It therefore formulated the objective technical problem as:

“how to partition a CU into TUs.”

Against that problem, the Board considered it obvious for the skilled person to use the dimensions of the largest transform kernel to determine whether a luma TU had to be split into smaller TUs.

The Board ultimately found claim 1 to lack inventive step over D1 combined with common general knowledge. It also observed that the claimed determinations of the maximum width and height appeared merely to specify intermediate mathematical steps and variables for arriving at the relationship between luma and chroma TB dimensions already disclosed in D1:

“The mere presence of intermediate mathematical constructs, without a recognisable technical effect, cannot involve an inventive step.”

5. Concluding Remarks

T 1385/25 highlights that, where an applicant relies on a particular technical effect for the assessment of inventive step, that effect must be directly and causally related to the technical features of the claimed invention, and the features contributing to that effect must be explicitly or implicitly specified in the claim.

So, when arguing that a distinguishing feature produces a particular technical effect, it may be useful to ask one further question:

Why does that effect occur?

And if the answer depends on additional technical conditions:

Are those conditions also derivable from the claim?

That may be an important step in moving from a technical feature to the technical effect relied upon for inventive step.

DISCLAIMER: The content of this website is provided for general informational purposes only and reflects the author's understanding of the law as of the date of publication. It does not constitute legal advice and should not be relied upon as a substitute for legal advice in any specific matter.

Subsequent developments in legislation, case law, administrative practice or official guidance may affect the accuracy or continued relevance of the content.