The Edge Impulse inferencing SDK expects a signal_t structure that contains sensor data - this is done so you don't need to load the full data into memory, but rather can page data in when needed. This signal_t structure expects data to be laid out in RGB888 format, but many cameras output data in RGB565 format instead. Additionally the classifier expects data in set dimensions (defined in EI_CLASSIFIER_INPUT_WIDTH / EI_CLASSIFIER_INPUT_HEIGHT) which might not be a native resolution of the camera. This example shows how to directly interact with an RGB565 frame buffer, by converting the data on the fly, and by creating a cutout when the resolutions don't match.

This is a full demonstration application that runs on macOS and Linux, but you'll only need the r565_to_rgb and cutout_get_data functions, plus the defines from main.cpp, on your embedded device. These functions have no external dependencies and build on any system where the Edge Impulse classifier runs.

To run this application:

1. Install the dependencies listed in Running your impulse locally on your desktop computer.

2. Build the application:

   $ sh build.sh
   

3. Run the application:

   $ ./build/edge-impulse-standalone
   

This has now created two files:

• framebuffer.bmp - a 'fake' framebuffer that was created in RGB565 format.
• from_signal.bmp - the image as received by the classifier. This went through RGB565->RGB888 conversion, and through the cutout.

Instead of just cutting out part of the image, you can also just crop down to the same aspect ratio, then squash/resize (bilinear interpolation) the rest of the image. This preserves more of your frame. To try this, run the following

make squash

Then run the application, same as above.

• framebuffer.bmp - The original, non squashed image
• squashed_from_signal.bmp - the image as received by the classifier. This was cropped, then squashed

Let us know on the forums.