Graph API

What it is?

• OpenCV 4.0 comes with a new experimental Graph API module (see opencv/modules/gapi). This is a new experimental API which allows to enable offload and optimizations for image processing / CV algorithms on pipeline level.

• The idea behind G-API is to declare image processing task in form of expressions and then submit it for execution – using a number of available backends. At the moment, there’s reference “CPU” (OpenCV-based) and experimental “Fluid’ backends available, with OpenCL (GPU) and other backends coming up next.

• G-API is an uncommon OpenCV module since it acts as a framework: it provides means for declaring operations, building graphs of operations, and finally implementing the operations for a particular backend. G-API model enforces separation between interfaces and implementations, so once an algorithm is expressed in G-API terms, it can be scaled/ported/offloaded to a new platform easily.

• G-API CPU (OpenCV) backend implements G-API standard functions using OpenCV itself (core/imgproc modules) and acts as a quick prototyping/porting/testing backend. If you have an image processing algorithm composed of OpenCV-like functions already, you would be able to switch quickly to G-API by using this backend.

• G-API Fluid backend implements a cache-efficient execution model and allows to save memory dramatically – e.g. a 1.5GB image processing pipeline fits into 750KB memory footprint with G-API/Fluid. G-API comes with a number of operations implemented for Fluid backend, so one can switch OpenCV/Fluid operations within a graph easily and even mix both in the same graph.

• Samples and documentation are WIP and will be completed during 4.0 release timeframe.