LED mosaic

Introduction

This project was inspired by the following post from Nick Loomis. The idea is to create a photomosaic built from those little 7-segment digit displays that you commonly find on microwaves, ovens, etc.

This is best explained with the following image:

First stage - replicating results

As a first step, I want to just re-create the results of Nick Loomis. He used 3 approaches:

Brightness representation

• Create candidate tiles which are each combination of LED segment on/off (2^7 == 128)
• Divide reference image into blocks with size equal to candidate tiles
• Calculate average brightness of each reference image block and choose candidate tile which has the closet brightness

Nearest neighbor feature matching

• Uses previous approach but instead of matching brightnesses, calculate vector distances of reference image blocks
• Choose candidate tile which has the minimum distance from the reference blocks (using e.g. L2-norm)

Mini-block averaging

• Uses a combination of previous approaches by first dividing the reference blocks and candidate tiles into smaller mini-blocks
• Calculate the average pixel value within each mini-block and choose candidate tile with minimum distance

Once I can experiment with these 3 techniques and am happy with the way the photomosaic looks for static images, I will move on to the second stage.

Second stage - camera feed

Here, I’ll create a real-time rendering of a camera/webcam feed and display it to the user. The main challenge here is latency. I want the transformed camera feed to update quick enough so that there is no noticeable lag between itself and the raw feed.

Third stage - physical system

This stage is a bit of a stretch goal. I want to create a physical system that performs the mosaic-generating algorithm using real 7-segment LED digits. Something like this Hackaday project but much larger. The idea would be to cover a large portion of a wall with a lot of 7-segment displays. A camera will be on top which will render the scene in front using the mosaic images and display this to the wall of digits. You can get a feel for how this would look on the bottom-right of the concept image.

A few major challenges with this are:

• cost: 7-segment displays are not very cheap, especially at the resolution I would require
• power: you typically want at least 10 mA of current through a single segment, and so this number blows up at scale
• latency: we need to have a quick refresh rate of the large digit grid, otherwise the scene displayed will lag behind the actual feed

If I do tackle this stage, I would love to display it as an art installation somewhere. I think it would be pretty cool to see a real-time rendering of yourself as a 7-segment display mosaic.