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CreatePerspectiveMap_Path

Creates a perspective transform map from planes defined by paths.

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

Syntax

C++
C#

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.