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Tools for radiometric calibration of consumer RGB(D) cameras

// repository documentation

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Consumer-grade color cameras suffer from significant optical nonlinearities,
often referred to as vignetting effects. For example, in Asus Xtion Pro Live
cameras the pixels in the corners are two times darker than those in the center
of the image. The vignetting effects in Intel RealSense cameras are less severe,
but are still noticeable, as can be seen below:

![Vignetting responses](https://raw.githubusercontent.com/taketwo/radical/master/doc/vignetting-responses.png "Vignetting responses")

Luckily, it is possible to calibrate the camera and remove the effects from the
images:

This repository contains a collection of apps to calibrate radiometric and
vignetting responses of a camera and a runtime library that you can link into
your project to load calibration files and radiometrically rectify the images
delivered by the camera.

Table of contents
-----------------

* [Requirements](#requirements)
* [Installation](#installation)
* [Calibration](#calibration)
    * [Radiometric response](doc/calibrate-radiometric-response.md)
    * [Vignetting response](doc/calibrate-vignetting-response.md)
* [Library usage](#library-usage)
* [Citing](#citing)
* [License](#license)

Requirements
------------

You need a compiler that supports C++11.

### Runtime library:

* OpenCV (2 or 3)

### Calibration apps:

* OpenCV (2 or 3)
  * Boost
  * OpenNI2 (optional, only if you want to calibrate an Asus Xtion camera)
  * librealsense (optional, only if you want to calibrate a RealSense camera)
  * Pylon SDK (optional, only if you want to calibrate a Pylon camera)
  * Ceres (optional, needed for radiometric calibration with Debevec method and
    for vignetting calibration with polynomial vignetting model)

Installation
------------

1. Clone this repository.

2. Configure the project. By default, both runtime library and calibration apps
   will be built. If only the runtime library is needed, then configure as
   follows:

```bash
   cmake .. -DBUILD_APPS=OFF
   ```

Note that if you want to enable support for Debevec camera response function
   calibration and fitting of polynomial vignetting model in the calibration
   app, you need to tell CMake where Ceres is installed:

```bash
   cmake .. -DCeres_DIR=<CERES_INSTALL_PATH>/share/Ceres
   ```

3. Install the project with `make install`.

Calibration
-----------

In order to radiometrically rectify images (e.g. invert the non-linear camera
response function and correct the vignetting effects), one needs to calibrate
the camera. Refer to the instructions below:

* [Calibrate radiometric response](doc/calibrate-radiometric-response.md)
* [Calibrate vignetting response](doc/calibrate-vignetting-response.md)

Library usage
-------------

In your *CMakeLists.txt* find the library as follows:

```cmake
   find_package(radical CONFIG REQUIRED)
   ```

And link it to your target:

```cmake
   target_link_libraries(your_target radical)
   ```

When configuring your project provide the path where *radical* was installed:

```bash
   cmake .. -Dradical_DIR=<RADICAL_INSTALL_PATH>/lib/cmake/radical
   ```

In you app include the headers:

```cpp
   #include <radical/radiometric_response.h>
   #include <radical/vignetting_response.h>
   ```

Load calibration files:

```cpp
   radical::RadiometricResponse rr("calibration-file-path.crf");
   radical::VignettingResponse vr("calibration-file-path.vgn");
   ```

Undo vignetting effects in frames coming from the camera:

```cpp
   cv::Mat frame;                 // color image from the camera
   cv::Mat irradiance, radiance;  // temporary storage
   cv::Mat frame_corrected;       // output image with vignette removed
   rr.inverseMap(frame, irradiance);
   vr.remove(irradiance, radiance);
   rr.directMap(radiance, frame_corrected);
   ```

Citing
------

If you use this in the academic context, please cite the following paper:

> **Calibration and Correction of Vignetting Effects with an Application to 3D
Mapping**, *S. V. Alexandrov, J. Prankl, M. Zillich, M. Vincze*, IROS'16

Licence
-------

MIT

radical

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