Main Content

reduce

Reduce density of points in ROI

所有的页面崩溃

Syntax

reduce(ROI)
减少(ROI,公差)

Description

example

reduce(ROI)reduces the number of points that define the region-of-interestROI. The ROI object stores the point array in thePositionproperty.reducereplaces the original value of thePositionproperty with the reduced value.

Thereducemethod calls thereducepolyfunction which uses the Ramer–Douglas–Peucker line simplification algorithm. This algorithm removes points along a straight line and leaves only knickpoints (points where the line curves).

example

reduce(ROI,tolerance)reduces the number of points that define theROI, wheretolerancespecifies the sensitivity of the reduction. Specify thetolerancevalue in the range[0,1].

Examples

collapse all

打开生活的脚本

Read an image into the workspace.

I = imread('cameraman.tif');

Display the image.

imshow(I);

Draw aFreehandROI on the image.

roi = drawfreehand;

View the number of points in thePositionproperty after completing the shape.

disp(['Original Size of Position property: 'mat2str(size(roi.Position))]);
Original Size of Position property: [272 2]

Use thereduceobject function to reduce the number of points required to define the shape.

reduce(roi)

View the reduced number of points in thePositionproperty.

disp(['Reduced Size of Position property: 'mat2str(size(roi.Position))]);
Reduced Size of Position property: [100 2]
打开生活的脚本

Read an image into the workspace.

I = imread('cameraman.tif');

Display the image.

imshow(I);

Draw aPolylineROI on the image.

roi = drawpolyline;

View the number of points in thePositionproperty after completing the shape.

disp(['Original Size of Position property: 'mat2str(size(roi.Position))]);
Original Size of Position property: [12 2]

Use thereduceobject function to reduce the number of points required to define the shape.

reduce(roi)

View the reduced number of points in thePositionproperty.

disp(['First try at reducing the number of points: 'mat2str(size(roi.Position))]);
First try at reducing the number of points: [12 2]

Note that the number of points is not changed. To improve the result, change the Tolerance parameter. By default, tolerance is set to .01. Increase the value and try it again.

reduce(roi,0.3)

View the size of thePositionproperty again. Changing the tolerance resulted in a reduction.

disp(['Reduction after resetting tolerance parameter: 'mat2str(size(roi.Position))]);
Reduction after resetting tolerance parameter: [4 2]

Input Arguments

collapse all

ROI object, specified as one of the following ROI objects:AssistedFreehand,Freehand,Polygon, andPolyline.

Sensitivity of reduction, specified as a number in the range [0, 1]. Increasing the tolerance increases the number of points removed. A tolerance value of0reduces a minimum number of points. A tolerance value of1results in the maximum reduction in points, leaving only the end points of the line.

Algorithms

The Ramer–Douglas–Peucker line simplification algorithm recursively subdivides a shape looking to replace a run of points with a straight line. The algorithm checks that no point in the run deviates from the straight line by more than the value specified bytolerance.

版本历史

Introduced in R2019b

See Also

||||

Topics