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.. vim: set fileencoding=utf-8 :
.. @author: Tiago de Freitas Pereira <tiago.pereira@idiap.ch>
.. @date: Mon Oct 19 11:10:18 CEST 2015
.. _bob.db.pola_thermal:
=============================
Polarimetric Thermal Database
=============================
Collected by USA Army, the Polarimetric Thermal Database contains basically VIS and Thermal face images.
Follow bellow the description of the imager used to capture this device.
The **polarimetric** LWIR imager used to collect this database was developed by Polaris Sensor Technologies.
The imager is based on the division-of-time spinning achromatic retarder (SAR) design that uses a spinning phase-retarder mounted in series with a linear wire-grid polarizer.
This system, also referred to as a polarimeter, has a spectral response range of 7.5-11.1, using a Stirling-cooled mercury telluride focal plane array with pixel array dimensions of 640×480.
A Fourier modulation technique is applied to the pixel readout, followed by a series expansion and inversion to compute the Stokes images.
Data were recorded at 60 frames per second (fps) for this database, using a wide FOV of 10.6°×7.9°. Prior to collecting data for each subject, a two-point non-uniformity correction (NUC) was performed using a Mikron blackbody at 20°C and 40°C, which covers the range of typical facial temperatures (30°C-35°C).
Data was recorded on a laptop using custom vendor software.
An array of four Basler Scout series cameras was used to collect the corresponding **visible spectrum imagery**.
Two of the cameras are monochrome (model # scA640-70gm), with pixel array dimensions of 659×494.
The other two cameras are color (model # scA640-70gc), with pixel array dimensions of 658×494.
The dataset contains 60 subjects in total.
For **VIS** images (considered only the 87 pixels interpupil distance) there are 4 samples per subject with neutral expression (called baseline condition **B**) and 12 samples per subject varying the facial expression (called expression **E**).
Such variability was introduced by asking the subject to count orally.
In total there are 960 images for this modality.
For the **thermal** images there are 4 types of thermal imagery based on the Stokes parameters (:math:`S_0`, :math:`S_1`, :math:`S_2` and :math:`S_3`) commonly used to represent the polarization state.
The thermal imagery is the following
- :math:`S_0`: The conventional thermal image
- :math:`S_1`
- :math:`S_2`
- DoLP: The degree-of-linear-polarization (DoLP) describes the portion of an electromagnetic wave that is linearly polarized, as defined :math:`\frac{sqrt(S_{1}^{2} + S_{2}^{2})}{S_0}`.
Since :math:`S_3` is very small and usually taken to be zero, the authors of the database decided not to provide this part of the data.
The same facial expression variability introduced in **VIS** is introduced for **Thermal** images.
The distance between the subject and the camera is the last source of variability introduced in the thermal images.
There are 3 ranges: R1 (2.5m), R2 (5m) and R3 (7.5m).
In total there are 11,520 images for this modality and for each subject they are split as the following:
+----------------+----------+----------+----------+
| Imagery/Range | R1 (B/E) | R2 (B/E) | R3 (B/E) |
+================+==========+==========+==========+
| :math:`S_0` | 16 (8/8) | 16 (8/8) | 16 (8/8) |
+----------------+----------+----------+----------+
| :math:`S_1` | 16 (8/8) | 16 (8/8) | 16 (8/8) |
+----------------+----------+----------+----------+
| :math:`S_2` | 16 (8/8) | 16 (8/8) | 16 (8/8) |
+----------------+----------+----------+----------+
| DoLP | 16 (8/8) | 16 (8/8) | 16 (8/8) |
+----------------+----------+----------+----------+
Documentation
-------------
.. toctree::
:maxdepth: 2
guide