[ VIGRA Homepage | Class Index | Function Index | File Index | Main Page ]

| Functors to Transform Images |
--- | --- | ---

## Classes

class | BrightnessContrastFunctor
| Adjust brightness and contrast of an image. More...
class | Threshold
| Threshold an image. More...
class | VectorNormFunctor
| A functor for computing the vector norm. More...
class | VectorNormSqFunctor
| A functor for computing the squared vector norm. More...

## Functions

template<class Multiplier, class DestValueType> LinearIntensityTransform< DestValueType, Multiplier > | linearIntensityTransform (Multiplier scale, DestValueType offset)
| Apply a linear transform to the source pixel values.
template<class SrcValueType, class DestValueType> LinearIntensityTransform< DestValueType, typename NumericTraits< DestValueType >::RealPromote > | linearRangeMapping (SrcValueType src_min, SrcValueType src_max, DestValueType dest_min, DestValueType dest_max)
| Map a source intensity range linearly to a destination range.

## Detailed Description

Note that the unary functors of the STL can also be used in connection with transformImage().

## Function Documentation

LinearIntensityTransform<DestValueType, Multiplier> linearIntensityTransform (...)

Apply a linear transform to the source pixel values.

Factory function for a functor that linearly transforms the source pixel values. The functor applies the transform '`destvalue = scale * (srcvalue + offset)`' to every pixel. This can, for example, be used to transform images into the visible range 0...255 or to invert an image.

If you leave out the second parameter / offset, you will get an optimized version of the functor which only scales by the given factor, however you have to make the template parameter (pixel type) explicit then.

Traits defined:

`FunctorTraits::isUnaryFunctor` is true (`VigraTrueType`)``

Declaration:

        namespace vigra {
            template <class Multiplier, class DestValueType>
            LinearIntensityTransform<DestValueType, Multiplier>
            linearIntensityTransform(Multiplier scale, DestValueType offset);

            template <class DestValueType, class Multiplier>
            ScalarIntensityTransform<DestValueType, Multiplier>
            linearIntensityTransform(Multiplier scale);
        }

Usage:

#include "vigra/transformimage.hxx"
Namespace: vigra

        vigra::IImage src(width, height);
        vigra::BImage dest(width, height);
        ...
        vigra::FindMinMax<IImage::PixelType> minmax;   // functor to find range

        vigra::inspectImage(srcImageRange(src), minmax); // find original range

        // transform to range 0...255
        vigra::transformImage(srcImageRange(src), destImage(dest),
                              linearIntensityTransform(
                                255.0 / (minmax.max - minmax.min), // scaling
                              - minmax.min));                    // offset

The one-parameter version can be used like this:

        // scale from 0..255 to 0..1.0
        FImage dest(src.size());

        vigra::transformImage(srcImageRange(src), destImage(dest),
                              linearIntensityTransform<float>(1.0 / 255));

Required Interface:

The source and destination value types must be models of LinearSpace in both cases.

LinearIntensityTransform<DestValueType, typename NumericTraits<DestValueType>::RealPromote> linearRangeMapping (...)

Map a source intensity range linearly to a destination range.

Factory function for a functor that linearly transforms the source pixel values. The functor applies the transform '`destvalue = scale * (srcvalue + offset)`' to every pixel, where `scale = (dest_max - dest_min) / (src_max - src_min)` and `offset = dest_min / scale - src_min`. As a result, the pixel values `src_max`, `src_min` in the source image are mapped onto `dest_max`, `dest_min` respectively. This works for scalar as well as vector pixel types.

Declaration:

        namespace vigra {
            template <class SrcValueType, class DestValueType>
            LinearIntensityTransform<DestValueType, typename NumericTraits<DestValueType>::RealPromote>
            linearRangeMapping(SrcValueType src_min, SrcValueType src_max,
                               DestValueType dest_min, DestValueType dest_max );
        }

Usage:

#include "vigra/transformimage.hxx"
Namespace: vigra

        vigra::IImage src(width, height);
        vigra::BImage dest(width, height);
        ...
        vigra::FindMinMax<IImage::PixelType> minmax;   // functor to find range

        vigra::inspectImage(srcImageRange(src), minmax); // find original range

        // transform to range 0...255
        vigra::transformImage(srcImageRange(src), destImage(dest),
                              linearRangeTransform(
                                minmax.min, minmax.max,               // src range
                                (unsigned char)0, (unsigned char)255) // dest range
                              );

Required Interface:

The source and destination value types must be models of LinearSpace in both cases.

© Ullrich Köthe (koethe@informatik.uni-hamburg.de) Cognitive Systems Group, University of Hamburg, Germany | html generated using doxygen and Python VIGRA 1.4.0 (21 Dec 2005)