Abstract
We present a face-classification architecture for long-wave infrared (IR) images implemented on a Field Programmable
Gate Array (FPGA). The circuit is fast, compact and low power, can recognize faces in real time and
be embedded in a larger image-processing and computer vision system operating locally on an IR camera. The
algorithm uses Local Binary Patterns (LBP) to perform feature extraction on each IR image. First, each pixel
in the image is represented as an LBP pattern that encodes the similarity between the pixel and its neighbors.
Uniform LBP codes are then used to reduce the number of patterns to 59 while preserving more than 90% of the
information contained in the original LBP representation. Then, the image is divided into 64 non-overlapping
regions, and each region is represented as a 59-bin histogram of patterns. Finally, the algorithm concatenates all
64 regions to create a 3,776-bin spatially enhanced histogram. We reduce the dimensionality of this histogram
using Linear Discriminant Analysis (LDA), which improves clustering and enables us to store an entire database
of 53 subjects on-chip. During classification, the circuit applies LBP and LDA to each incoming IR image in real
time, and compares the resulting feature vector to each pattern stored in the local database using the Manhattan
distance. We implemented the circuit on a Xilinx Artix-7 XC7A100T FPGA and tested it with the UCHThermalFace
database, which consists of 28 81 x 150-pixel images of 53 subjects in indoor and outdoor conditions.
The circuit achieves a 98.6% hit ratio, trained with 16 images and tested with 12 images of each subject in the
database. Using a 100 MHz clock, the circuit classifies 8,230 images per second, and consumes only 309mW.
