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CreatePerspectiveMap_Path

Header:	AVL.h
Namespace:	avl
Module:	Calibration

Creates a perspective transform map from planes defined by paths.

Applications: Data preprocessing for fast perspective correction. The result is used by RemapImage.

Syntax

void avl::CreatePerspectiveMap_Path
(
	const avl::ImageFormat& inImageFormat,
	atl::Optional<const avl::Region&> inRoi,
	const avl::Path& inImagePath,
	atl::Optional<const avl::Path&> inTargetPath,
	atl::Optional<const avl::Size&> inNewSize,
	const avl::InterpolationMethod::Type inInterpolationMethod,
	avl::SpatialMap& outSpatialMap,
	avl::Matrix& outTransformMatrix
)

Parameters

Name	Type	Default	Description
inImageFormat	const ImageFormat&
inRoi	Optional<const Region&>	NIL	Range of pixels to be processed
inImagePath	const Path&		Plane defined by a closed path made of 4 points
inTargetPath	Optional<const Path&>	NIL	Target plane. If NIL then image corners are used starting from (0,0) (Width, 0) (Width, Height), (0, Height)
inNewSize	Optional<const Size&>	NIL	New image size after remapping
inInterpolationMethod	const InterpolationMethod::Type		Interpolation method used in extraction of image pixel values
outSpatialMap	SpatialMap&		Calculated spatial map
outTransformMatrix	Matrix&		Used transform matrix

Description

This operation computes a SpatialMap which can be later used for removing a perspective distortion from an image.

The operation maps the input path (inImagePath) into the target path (inTargetPath). If the inTargetPath input is set to Auto this path will be made from the corner points of the input image. Both paths must be closed and must be made of four points.

The input inNewSize allows rescaling of the output image.

The inImageFormat format is necessary for preparation of a spatial map.

The outTransformMatrix output allows verifying the found transformation.

Examples

Image before and after the perspective transform created by CreatePerspectiveMap_Path.

Remarks

This filter is a good choice for local perspective distortion removal - such as "unwrapping" boxes, as is depicted by the example above. Applications concerned with observing real-world flat surfaces (such as observing conveyor belts) should use methods that are more accurate. Please refer to: Machine Vision Guide - Camera Calibration and World Coordinates

Notice that both inImagePath path and inTargetPath must be made of four points. This filter creates point to point transform so the changing points order in paths may yield an unexpected result.

The best way to understand the relation between inImagePath and inTargetPath is to present the first of them on the input image and the second on the background of remapped image.

The image before remapping on the left (with inImagePath) and the image after on the right (with inTargetPath).

Errors

List of possible exceptions:

Error type	Description
DomainError	inImagePath input must contain a closed path created from 4 points in CreatePerspectiveMap_Path.
DomainError	inTargetPath input must contain a closed path created from 4 points in CreatePerspectiveMap_Path.