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Advanced Image Processing Techniques for Maximum Efficiency

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Learn about traditional vs. generic image processing, benefits of standard template library, and implementing versatile algorithms with multidimensional locators. Discover the power of generic programming in C++ for high-performance, portable image processing applications.

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Advanced Image Processing Techniques for Maximum Efficiency

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  1. www.ngi-central.org

  2. Traditional Image Processing • Data Structures • Images, Palettes, Histograms, Profiles, etc. • Formanydatatypes (8bit, 16 bit, float, etc.) • Algorithms • Dependent on Data Structures • Dependent on datatypes • Combinatorial Explosion -> unmanageable • Toimplementonenewalgorithm, it must bewrittenmanytimes – foreach type www.ngi-central.org

  3. Generic Image Processing • GenericProgrammingcomestotherescue • Threekey design techniques • Iteratorsdecoupledatastructures and algorithms • Functorsallowtoexchangepartsofcomputation • Genericalgorithms in termsofabstractiterators and functors • Enablingtechnologyofcompilersisthetemplate<> mechanism www.ngi-central.org

  4. Standard Template Library • STL is an implementationofgenericprogrammingconcepts • STL isavailablewith all compilerssinceitispartofthe C++ standard • STL isaround 10 yearsold and consideredmature • Educational material tolearngenericprogramming in generaland STL in particularisavailable www.ngi-central.org

  5. Example: RGB to Gray • Using STL style programming structRGBValue { unsignedcharred, green, blue; }; structRGBToGray { unsignedcharoperator()(constRGBValue& rgb) const { return 0.3*rgb.red + 0.59*rgb.green + 0.11*rgb.blue; } }; vector<RGBValue> rgb; vector<unsignedchar> gray; ... transform(rgb.begin(), rgb.end(), gray.begin(), RGBToGray()); www.ngi-central.org

  6. New:worksfor all types! Betterexample • Templated on thedatatype • <template class T> • struct RGBValue { • T red, green, blue; • }; • <template class T> • struct RGBToGray { • T operator()(const RGBValue<T>& rgb) const { • return 0.3*rgb.red + 0.59*rgb.green + 0.11*rgb.blue; • } • }; • vector<RGBValue<float> > rgb; • vector<float> gray; • ... • transform(rgb.begin(), rgb.end(), gray.begin(), RGBToGray<float>()); www.ngi-central.org

  7. STL leavesthingstodesire • STL isdesignedtoworkwith 1D data • Images areinherentlytwo(multi)dimensional • Somealgorithms do not needthedimensionality • Use STL in thiscase • Somealgorithmsneedthedimensionality • Cannotuse STL, needsomething different www.ngi-central.org

  8. Multidimensional Locators • A locatoris a multidimensional iterator • Logical extensionto an iterator Move theiterator ++it; --it; it+=100; it-=50; Move thelocator ++it.x; --it.y; it.x+=100; it.y-=50; www.ngi-central.org

  9. Algorithms change as well • // STL implementation • template<class IT, class F> • IT transform(IT First, IT Last, IT Dest, F Func) • { • for (; First != Last; ++First, ++Dest) • *Dest = Func(*First); • return (Dest); • } • // 2D implementation • template<class IT, class F> • IT transform(IT First, IT Last, IT Dest, F Func) • { • for (; First.y != Last.y; ++First.y, ++Dest.y) • for (; First.x != Last.x; ++First.x, ++Dest.x) • *Dest = Func(*First); • return (Dest); • } www.ngi-central.org

  10. What do wegain? • An algorithmliketransformreplacesmanyfunctions in traditional programming style • Itcan do this, becauseitistemplated on thefunction • We still needtoprogramthefunctionality, but decoupledfromnavigation • Itsavesustorewritetheloopsmanytimes • Bonus: thefunctionobjectscanbereused in completely different algorithmsas well • Itcan do this, becauseitistemplated on thedatatype (byiteratorindirection) • Itsavesustorewritethecompletethingforeachdatatype • The gainistremendous (time, functionality, flexibility) www.ngi-central.org

  11. NGI - Goals • Image Processing • Image -> Image • Image Analysis • Image -> Numbers • Generic Library • C++ • Templates • Source code • Independence of type • High Performance • nopenaltyforgenericcode • Portability • clean sourcecodefor easy portability www.ngi-central.org

  12. Directory Structure • Code (include/) • Third partycode (toolkits/) • Documentation (book/, reference/, presentations/) • Sample code (samples/) and sample images (images/) • Automated tests (tests/) www.ngi-central.org

  13. NGI - Tests • Unit Tests • Features of a class/functionaretested in isolation • Regression Tests • Outcomeof a functionistestedforregressions • Image/Text comparisons (now == previous) • Benchmarks • Measured in clocks per pixel www.ngi-central.org

  14. NGI - Documentation • User Documentation • NGI Book • Reference Documentation • BuiltwithDoxygenfromsourcecode (HTML) • Alwaysup-to-date www.ngi-central.org

  15. Third Party Code • Mandatory • boost (www.boost.org) • Optional • FreeImage (freeimage.sourceforge.net) • Cairo (www.cairographics.org) www.ngi-central.org

  16. NGI – Build System • CMakeisusedasbuildengine • modular • selectcompiler(VS2005, VS2008, VS2010, Intel) • runtests • builddocumentation • Currentlysettingup a continuousbuildmachinewithvariousvirtualbuildenvironments www.ngi-central.org

  17. Sample Code • Manycodesamples • Consolesamples • MFC samples • .NET samples • Tests are also samples • UsingBoost.Test • Unit tests, benchmarks, regressiontests www.ngi-central.org

  18. NGI – Guidelines • Header onlylibrary • Source code • Heavy useoftemplates • Concentration on coreissues • usingother Open Source librarieswhereapplicable • Boost, FreeImage, Cairo, Qt www.ngi-central.org

  19. NGI – Concepts • Buffer • storesdata • handlesallocation and deallocation • canuseexternalbuffers • View • levelofindirection • light, just a pointer and a fewpitches • all accessesthroughviews • can handle foreigndatabuffers • viewmanipulations • sub-views (moving_view.exe) • rotatedviews (dimension_swap_view.exe) • reversescanningdirections (reverse_view.exe) • subsampling (subsampling_view.exe) www.ngi-central.org

  20. NGI – FunctionalityOverview (1) • Basic functionsusedeverywhereelse • Interpolation • linear, spline • Geometry • point, line_segment, ray, line, triangle, quadrilateral, rectangle, polygon, circle, ellipse • widgetsfor all geometricelements • Other examples • Base64, ZIP/GZIP Compression/Decompression, Fixed point, Matrix solver, solvingquadratic and cubicequations, etc. www.ngi-central.org

  21. NGI – FunctionalityOverview (2) • STL likefunctions • copy, count, equal, find, ... • Image Processing functions • Point, Filters, Morphology, ... • Image Analysis functions • Blob, Pattern match, OCR/OCV, ... • Display Engine • Images, Palettes, Curves, Widgets, Geometry, ... • Framegrabber/Camerainterface www.ngi-central.org

  22. NGI – STL LikeFunctions • accumulate • copy • count • equal • fill • find • generate • inner_product • max_element • min_element • replace • transform www.ngi-central.org

  23. NGI – Image Processing Functions (1) • Point functions (point_operations.exe, profile.exe) • Filter and morphologicalfunctions (neighborhood_operations.exe) • 1D, 2D, 3D • Separable • Fast box filters – independentofkernelsize • Manypredefinedkernels, usercaneasilyadd • Framing (framing.exe) • Erode, Dilate, Open, Close, Gradient • Gray and binarybehavior www.ngi-central.org

  24. NGI – Image Processing Functions (2) • Binning (binning.exe) • binningmethodselectable/userwritable • Geometric Transformation (resample.exe) • affine / polar • choiceofresampling filter (nearestneighbor, box, triangle, quadratic, cubic, bspline, sinc, kaiser, lanczos) • Autofocus • based on variance, gradient www.ngi-central.org

  25. NGI – Image Processing Functions (3) • Color Processing • Color models (color_transform.exe) • RGB, CMY(K), HLS, HSI, Lab, Lchab, Luv, Lchuv • Color twist (color_twist.exe) • Bayer demosaic • StatisticFunctions • min, max, average, variance, percentiles • CameraCalibration www.ngi-central.org

  26. NGI – Image Analysis Functions (1) • Blob analysis • Thresholding via Otsu‘smethod • 2D, 3D Labelling • Fläche/Volumen • Chain Code (inner, outer), perimeter • Moments • binary, gray • ordinary, central, Hu, Flusser www.ngi-central.org

  27. NGI – Image Analysis Functions (2) • Pattern matching and searching (search.exe) • grayorcolor • usingpyramidforacceleration • OCR/OCV • train a characterset • read/verifytext www.ngi-central.org

  28. NGI - Acceleration • Writtenfor Multi-Core • UsesOpenMP • Most functionsscalenicely, canbeseenwiththebenchmarks • Working on SIMD acceleration • Vector Processing (128 bytechunks) • 16 Pixels at a time • First forpointfunctions • These twomethodsare orthogonal www.ngi-central.org

  29. NGI – Display Engine (1) • Display Engine • Direct2D, GDI Plus, OpenGL, Cairo • Alpha channel support (blit.exe) • Images (file_access.exe) • Palettes (palette.exe, false_color.exe) • Curves (histogram.exe) www.ngi-central.org

  30. NGI – Display Engine (2) • Widgets (scale.exe) • Hierarchicalwidgetcomposition(widget_box.exe) • Callbacksfor smart interaction(horizontal_cursor.exe) www.ngi-central.org

  31. NGI – Framegrabber/Camera • Grabbingintoringbuffer • asynchronous on different thread • live/snapshot • pre-trigger/post-trigger • Gen<i>cam support planned www.ngi-central.org

  32. More Information www.ngi-central.org ngi-central.blogspot.com peter@ngi-central.org www.ngi-central.org

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