1. Sirius by CS


Sirius by CS-SI

A fast resampling software with simple to plugin library.

Overview • Docker App • How To Build • How To Use • Acknowledgement

CS

As of today, and to our knowledge, there is no complete open source resampling tool for satellite imagery based on frequency resampling. Numerous softwares, some being open source, can be found to resample (most of the time upsample) data. Most of them offers various interpolators (GIMP, Pandore, Getreuer, OTB), some being very fast but rather innacurate (nearest neighbors, bilinear) and some offering high quality results (more often than not based on a Lancsoz convolutional kernel) but being very time consuming. Then only a few provides ways to deal efficiently with large amount of data (OTB) or proposes a fast and accurate sinus cardinal interpolator implemented as frequencial zero padding (Getreuer). None of those however allows one to resample satellite images in frequency domain with a floating upscaling or downscaling factor.

It could be argued that the OTB remains the best solution for the purpose of resampling satellite images. However, and though there exists ways to filter satellite images in frequency domain with the OTB, it is not possible to resample such an image in frequency domain.

Sirius then aims at filling this void offering a fast and simple to plug-in resampling C++ library that is taking advantage of the Fourier Transform.

1.2. Docker App

Sirius is delivered inside a docker container. Assuming one has previously installed docker, then Sirius can be launched using the following commands :

# pull image from the registry
docker pull ldumas/sirius_dockerfile:sirius
# then run sirius
docker run ldumas/sirius_dockerfile:sirius [OPTION...] input-image output-image

# if no arguments are set then sirius is launched without any argument and its help is displayed
# see below for the list of sirius args

# note that using docker volume might be a good solution to give the container access to input-image
# and to give host access to the output-image :
docker run -v /home/user/outdir/:/outdir -v /home/user/input_images:/input ldumas/sirius_dockerfile:sirius /input/input-image.tif /outdir/output-image.tif -r 1:2

1.3. How to Build

Sirius is using CMake to build its libraries and executables.

1.3.1. Requirements

  • C++14 compiler (GCC >= 5)
  • CMake >=3.2
  • GDAL development kit, >=2
  • FFTW development kit, >=3
  • Doxygen if documentation option is enabled

1.3.3. Options

  • CMAKE_BUILD_TYPE: Debug, Release, RelWithDebInfo or MinSizeRel
  • CMAKE_INSTALL_PREFIX: directory path where the built artifacts (include directory, library, docs) will be gathered using install target
  • SIRIUS_VERSION: set Sirius library version (default is 0.0.0)
  • SIRIUS_REVISION_COMMIT: set Sirius library revision commit (default is sirius-no-revision-commit)
  • ENABLE_CACHE_OPTIMIZATION: set to ON to build with cache optimization for FFTW and Filter
  • ENABLE_GSL_CONTRACTS: set to ON to build with GSL contracts (e.g. bounds checking). This option should be OFF on release mode.
  • ENABLE_LOGS: set to ON if you want to build Sirius with the logs
  • ENABLE_UNIT_TESTS: set to ON if you want to build the unit tests
  • ENABLE_DOCUMENTATION: set to ON if you want to build the documentation

Sirius version can be extracted from git describe and revision commit from git rev-parse HEAD.

1.3.4. Example

# CWD is Sirius root directory
GIT_COMMIT=$(git rev-parse HEAD)
GIT_DESCRIBE=$(git describe 2> /dev/null)
if [ "x${GIT_DESCRIBE}" = "x" ]; then
    GIT_DESCRIBE="0.0.0"
fi

mkdir .build
cd .build
cmake .. -DCMAKE_BUILD_TYPE=Release \
         -DCMAKE_INSTALL_PREFIX=/tmp/sirius \
         -DSIRIUS_VERSION=${GIT_DESCRIBE} \
         -DSIRIUS_REVISION_COMMIT=${GIT_COMMIT} \
         -DENABLE_CACHE_OPTIMIZATION=ON \
         -DENABLE_GSL_CONTRACTS=OFF \
         -DENABLE_LOGS=ON \
         -DENABLE_UNIT_TESTS=OFF \
         -DENABLE_DOCUMENTATION=ON
cmake --build . --target sirius
cmake --build . --target doc
cmake --build . --target install

See also .travis/create_cmake_project.sh

1.4. How to use

1.4.1. Host requirements

1.4.2. Sirius standalone tool

Sirius is shipped as a standalone tool that offers filtering and resampling features.

$ ./sirius -h
Sirius X.Y.Z (...)
Standalone tool to resample and filter images in the frequency domain

Usage:
  ./sirius [OPTION...] input-image output-image

  -h, --help           Show help
  -v, --verbosity arg  Set verbosity level
                       (trace,debug,info,warn,err,critical,off) (default: info)

 resampling options:
  -r, --resampling-ratio arg    Resampling ratio as input:output, allowed
                                format: I (equivalent to I:1), I:O (default: 1:1)
      --no-image-decomposition  Do not decompose the input image (default:
                                periodic plus smooth image decomposition)
      --upsample-periodization  Force periodization as upsampling algorithm
                                (default algorithm if a filter is provided). A
                                filter is required to use this algorithm
      --upsample-zero-padding   Force zero padding as upsampling algorithm
                                (default algorithm if no filter is provided)

 filter options:
      --filter arg           Path to the filter image to apply to the source
                             or resampled image
      --filter-normalize     Normalize filter coefficients (default is no
                             normalization)
      --zero-pad-real-edges  Force zero padding strategy on real input edges
                             (default: mirror padding)
      --hot-point-x arg      Hot point x coordinate (considered centered if
                             no value is provided)
      --hot-point-y arg      Hot point y coordinate (considered centered if
                             no value is provided)

 streaming options:
      --stream                  Enable stream mode
      --block-width arg         Initial width of a stream block (default:
                                256)
      --block-height arg        Initial height of a stream block (default:
                                256)
      --no-block-resizing       Disable block resizing optimization
      --parallel-workers [=arg(=1)]
                                Parallel workers used to compute resampling
                                (8 max) (default: 1)

1.4.2.1. Processing mode options

1.4.2.1.1. Regular mode

Regular mode (default mode) will put the whole image in memory and then processed it. This mode should only be used on small image.

The following command line will zoom in the image /path/to/input-file.tif by 4/3 with the periodic plus smooth image decomposition, apply the filter /path/to/filter-image-4-3.tif to the zoomed image and write the result into /path/to/output-file.tif.

./sirius -r 4:3 \
         --filter /path/to/filter-image-4-3.tif \
         /path/to/input-file.tif /path/to/output-file.tif
1.4.2.1.2. Stream mode

Stream mode is activated with the option --stream. It will cut the image into multiple blocks of small size (default block size is 256x256). Each block will be processed separately and result blocks will be aggregated to generate the output image. This mode must be used on large image.

Stream mode can be run in mono-threaded context (--parallel-workers=1) or in multi-threaded context (--parallel-workers=N where N is the requested number of threads which will compute the resampling).

./sirius -r 4:3 \
         --stream --parallel-workers=4 \
         --filter /path/to/filter-image-4-3.tif \
         /path/to/input-file.tif /path/to/output-file.tif

It is possible to customize block size with the options --block-witdh=XXX and --block-height=YYY.

Default behavior tries to optimize given block size so that the processed block (block size + filter margins) width and height are dyadic. You can disable this optimization with the option --no-block-resizing.

When dealing with real zoom, block width and height are computed so that they comply with the zoom ratio.

1.4.2.2. Resampling options

Resampling ratio is specified with the option -r. Expected format ratios are:

  • -r INPUT_RESOLUTION where INPUT_RESOLUTION is a positive integer (e.g. -r 2).
  • -r INPUT_RESOLUTION:OUTPUT_RESOLUTION where INPUT_RESOLUTION and OUTPUT_RESOLUTION are positive integers (e.g. -r 2:1).

Sirius can use two image decomposition algorithms:

  • Periodic plus Smooth (default behavior) is splitting the input image into a periodic part and a smooth image part.
  • None (--no-image-decomposition) is using raw image data without any processing.

Sirius can use two upsampling strategies:

  • Periodization: default behavior if a filter is provided.
  • Zero padding: default algorithm if no filter is provided.

Upsampling strategies can be forced with the following options:

  • --upsampling-zero-padding
  • --upsampling-periodization

Force periodization upsampling without providing a filter will result in an error.

More details on algorithms in the Theoretical Basis documentation.

1.4.2.3. Filter options

A filter image path can be specified with the option --filter. This filter will be applied:

  • on the resampled image if the image is upsampled.
  • on the source image if the image is downsampled.

Default behavior will pad real input edges with a mirroring of the edges. --zero-pad-real-edges will change this strategy and zero pad real input edges.

It is assumed that the filter is already normalized. If not, the option --filter-normalize will normize it before any processing.

Finally, it is possible to give a filter which has an uncentered hot point by specifying its coordinates thanks to --hot-point-x and --hot-point-y options. In this case sirius will center the filter’s hot point before any processing.

More details on filters in the Theoretical Basis documentation.

1.4.2.4. Examples

1.4.2.4.1. Zoom in

The following command line will zoom in input/lena.jpg by 2 using periodic plus smooth image decomposition and zero padding upsampling.

./sirius -r 2:1 \
         --upsample-zero-padding \
         input/lena.jpg output/lena_z2.jpg

The following command line will zoom in input/lena.jpg by 2 using periodic plus smooth image decomposition, periodization upsampling and filter for upsampling 2.

./sirius -r 2 \
         input/lena.jpg output/lena_z2.jpg

The following command line will zoom in input/sentinel2_20m.tif by 2 using stream mode and 8 workers, periodic plus smooth image decomposition, periodization upsampling and filter for upsampling 2.

./sirius --stream --parallel-workers=8 \
         -r 2 \
         --filter filters/ZOOM_2.tif \
         input/sentinel2_20m.tif output/sentinel2_20m_z2.tif
1.4.2.4.2. Zoom out

The following command line will zoom out input/lena.jpg by 1/2 using periodic plus smooth image decomposition and filter for downsampling 1/2.

./sirius -r 1:2 \
         --filter filters/ZOOM_1_2.tif \
         input/lena.jpg output/lena_z2.jpg

The following command line will zoom out input/disparity.png by 1/2 using periodic plus smooth image decomposition and filter for downsampling 1/2.

./sirius -r 1:2 \
         --filter filters/ZOOM_1_2.tif \
         input/disparity.png output/disparity_z1_2.jpg

The following command line will zoom out input/sentinel2_10m.tif by 1/2 using using stream mode and 8 workers, periodic plus smooth image decomposition and filter for downsampling 1/2.

./sirius --stream --parallel-workers=8 \
         -r 1:2 \
         --filter filters/ZOOM_1_2.tif \
         input/sentinel2_10m.tif output/sentinel2_10m_z1_2.tif

1.4.3. Sirius library API

Sirius is designed to be easy to use.

The main interface to compute a frequency resampling is IFrequencyResampler and it only requires an image, a zoom ratio and an optional filter.

IFrequencyResampler objects are instantiated by the FrequencyResamplerFactory.

1.4.3.1. Example without filter

#include "sirius/filter.h"
#include "sirius/frequency_resampler_factory.h"
#include "sirius/image.h"
#include "sirius/types.h"

// create an image
sirius::Image image = {...};

// configure the zoom ratio
sirius::ZoomRatio zoom_ratio = sirius::ZoomRatio::Create(7, 5);

// compose a frequency resampler from sirius::ImageDecompositionPolicies and
//     sirius::FrequencyZoomStrategies enums
sirius::IFrequencyResampler::UPtr freq_resampler =
      sirius::FrequencyResamplerFactory::Create(
            sirius::ImageDecompositionPolicies::kPeriodicSmooth,
            sirius::FrequencyZoomStrategies::kZeroPadding);

// compute the resampled image
sirius::Image resampled_image = freq_resampler->Compute(
      zoom_ratio, image, {}, {});

1.4.3.2. Example with filter

#include "sirius/filter.h"
#include "sirius/frequency_resampler_factory.h"
#include "sirius/image.h"
#include "sirius/types.h"

// create an image
sirius::Image image = {...};

// configure the zoom ratio
sirius::ZoomRatio zoom_ratio = sirius::ZoomRatio::Create(7, 5);

// create a filter from an image file
sirius::Filter filter = sirius::Filter::Create("/path/to/filter/image_7_5.tif",
                                               zoom_ratio);

// compose a frequency resampler from sirius::ImageDecompositionPolicies and
//     sirius::FrequencyZoomStrategies enums
sirius::IFrequencyResampler::UPtr freq_resampler =
      sirius::FrequencyResamplerFactory::Create(
            sirius::ImageDecompositionPolicies::kPeriodicSmooth,
            sirius::FrequencyZoomStrategies::kPeriodization);

// compute the resampled image
sirius::Image resampled_image = freq_resampler->Compute(
      zoom_ratio, image, filter.padding(), filter);

1.4.3.3. Thread safety

Compute a resampled image with Sirius is thread safe so it is possible to use the same IFrequencyResampler object in a multi-threaded context.

Process an image with a Filter object is also thread safe so you can reuse the same filter in a multi-threaded context.

1.5. Unit tests

Running tests requires data features (input image, filters) which are available here.

You need to execute the tests in the root directory of those data features. Expected directory tree is:

ROOT_DATA_FEATURES/input
                  /filters
                  /output

frequency_resampler_tests and functional_tests will create output images in the directory ROOT_DATA_FEATURES/output

1.6. Acknowledgement

Sirius developers would like to thank: