equ_histo_image_rectequ_histo_image_rectEquHistoImageRectEquHistoImageRectequ_histo_image_rect (Operator)
Name
equ_histo_image_rectequ_histo_image_rectEquHistoImageRectEquHistoImageRectequ_histo_image_rect — Histogram linearization within a rectangluar mask.
Signature
Herror equ_histo_image_rect(const Hobject Image, Hobject* ImageEquHisto, const char* Mode, const Hlong MaskWidth, const Hlong MaskHeight, double MaxContrast)
Herror T_equ_histo_image_rect(const Hobject Image, Hobject* ImageEquHisto, const Htuple Mode, const Htuple MaskWidth, const Htuple MaskHeight, const Htuple MaxContrast)
void EquHistoImageRect(const HObject& Image, HObject* ImageEquHisto, const HTuple& Mode, const HTuple& MaskWidth, const HTuple& MaskHeight, const HTuple& MaxContrast)
HImage HImage::EquHistoImageRect(const HString& Mode, Hlong MaskWidth, Hlong MaskHeight, const HTuple& MaxContrast) const
HImage HImage::EquHistoImageRect(const HString& Mode, Hlong MaskWidth, Hlong MaskHeight, double MaxContrast) const
HImage HImage::EquHistoImageRect(const char* Mode, Hlong MaskWidth, Hlong MaskHeight, double MaxContrast) const
HImage HImage::EquHistoImageRect(const wchar_t* Mode, Hlong MaskWidth, Hlong MaskHeight, double MaxContrast) const
(Windows only)
static void HOperatorSet.EquHistoImageRect(HObject image, out HObject imageEquHisto, HTuple mode, HTuple maskWidth, HTuple maskHeight, HTuple maxContrast)
HImage HImage.EquHistoImageRect(string mode, int maskWidth, int maskHeight, HTuple maxContrast)
HImage HImage.EquHistoImageRect(string mode, int maskWidth, int maskHeight, double maxContrast)
Description
The operator equ_histo_image_rectequ_histo_image_rectEquHistoImageRectEquHistoImageRectEquHistoImageRectequ_histo_image_rect enhances the contrast.
Similar to equ_histo_imageequ_histo_imageEquHistoImageEquHistoImageEquHistoImageequ_histo_image, it applies a transformation to linearize
the cumulative histogram. However, instead of using the histogram of the
whole image, only the local neighborhood of each pixel is considered to
compute the transformation. The size of this rectangular neighborhood region
can be set by MaskWidthMaskWidthMaskWidthMaskWidthmaskWidthmask_width and MaskHeightMaskHeightMaskHeightMaskHeightmaskHeightmask_height.
The local contrast maximization improves the visibility of low-contrast
structures, but also amplifies noise. The parameter MaxContrastMaxContrastMaxContrastMaxContrastmaxContrastmax_contrast can
be used to limit the maximum contrast in a local neighborhood, which
effectively reduces the amplification of noise. Therefore, the method is also
known as Contrast-Limited Adaptive Histogram Equalization (CLAHE).
The parameter ModeModeModeModemodemode determines the processing mode.
In the 'accurate'"accurate""accurate""accurate""accurate""accurate" mode, the transformation is computed for each
pixel as described above.
In the 'fast'"fast""fast""fast""fast""fast" mode, the transformation is computed only for a subset
of all pixels and interpolated between those points.
Due to the interpolation, the results of both modes can differ significantly.
Attention
The operator equ_histo_image_rectequ_histo_image_rectEquHistoImageRectEquHistoImageRectEquHistoImageRectequ_histo_image_rect primarily serves for
optical processing of images for a human viewer. For example, the
contrast spreading can lead to a detection of fictitious edges.
Note that filter operators may return unexpected results if
an image with a reduced domain is used as input. Please refer to the
chapter Filters.
Execution Information
- Multithreading type: reentrant (runs in parallel with non-exclusive operators).
- Multithreading scope: global (may be called from any thread).
- Automatically parallelized on tuple level.
- Automatically parallelized on channel level.
- Automatically parallelized on domain level.
Parameters
ImageImageImageImageimageimage (input_object) (multichannel-)image(-array) → objectHImageHObjectHImageHobject (byte)
Image to be enhanced.
ImageEquHistoImageEquHistoImageEquHistoImageEquHistoimageEquHistoimage_equ_histo (output_object) (multichannel-)image(-array) → objectHImageHObjectHImageHobject * (byte)
Image with linearized gray values.
ModeModeModeModemodemode (input_control) string → HTuplestrHTupleHtuple (string) (string) (HString) (char*)
Processing mode.
Default value:
'accurate'
"accurate"
"accurate"
"accurate"
"accurate"
"accurate"
Suggested values: 'accurate'"accurate""accurate""accurate""accurate""accurate", 'fast'"fast""fast""fast""fast""fast"
MaskWidthMaskWidthMaskWidthMaskWidthmaskWidthmask_width (input_control) extent.x → HTupleintHTupleHtuple (integer) (int / long) (Hlong) (Hlong)
Width of the filter mask.
Default value: 51
Suggested values: 31, 51, 101, 151
Typical range of values: 1
≤
MaskWidth
MaskWidth
MaskWidth
MaskWidth
maskWidth
mask_width
Minimum increment: 2
Restriction: MaskWidth <= width(Image)
MaskHeightMaskHeightMaskHeightMaskHeightmaskHeightmask_height (input_control) extent.y → HTupleintHTupleHtuple (integer) (int / long) (Hlong) (Hlong)
Height of the filter mask.
Default value: 51
Suggested values: 31, 51, 101, 151
Typical range of values: 1
≤
MaskHeight
MaskHeight
MaskHeight
MaskHeight
maskHeight
mask_height
Minimum increment: 2
Restriction: MaskHeight <= height(Image)
MaxContrastMaxContrastMaxContrastMaxContrastmaxContrastmax_contrast (input_control) real → HTupleUnion[float, int]HTupleHtuple (real / integer) (double / int / long) (double / Hlong) (double / Hlong)
Maximum contrast.
Default value: 0.01
Suggested values: 0, 0.01, 0.02, 0.05, 0.1, 0.5, 1
Typical range of values: 0
≤
MaxContrast
MaxContrast
MaxContrast
MaxContrast
maxContrast
max_contrast
≤
1
Restriction: 0 <= MaxContrast <= 1
Complexity
In ModeModeModeModemodemode='accurate'"accurate""accurate""accurate""accurate""accurate", equ_histo_image_rectequ_histo_image_rectEquHistoImageRectEquHistoImageRectEquHistoImageRectequ_histo_image_rect uses an
algorithm with constant complexity per pixel, i.e., the runtime only depends
on the size of the input image and not on the mask size.
In ModeModeModeModemodemode='fast'"fast""fast""fast""fast""fast", the number of histograms to be computed
depends on the mask size. Hence, the runtime increases with smaller mask
sizes and decreases with larger mask sizes.
Possible Successors
disp_imagedisp_imageDispImageDispImageDispImagedisp_image
Alternatives
equ_histo_imageequ_histo_imageEquHistoImageEquHistoImageEquHistoImageequ_histo_image,
scale_imagescale_imageScaleImageScaleImageScaleImagescale_image,
scale_image_maxscale_image_maxScaleImageMaxScaleImageMaxScaleImageMaxscale_image_max,
illuminateilluminateIlluminateIlluminateIlluminateilluminate
See also
equ_histo_imageequ_histo_imageEquHistoImageEquHistoImageEquHistoImageequ_histo_image,
scale_imagescale_imageScaleImageScaleImageScaleImagescale_image
References
S. Pizer et al.: “Adaptive Histogram Equalization and Its Variations”.
Computer Vision, Graphics, and Image Processing 39, pp. 355-368, 1987.
Module
Foundation