ROI-Based Processing

Define and operate on regions of interest (ROI)

A region of interest (ROI) is a portion of an image that you want to filter or operate on in some way. You can represent an ROI as a binary mask image. In the mask image, pixels that belong to the ROI are set to 1 and pixels outside the ROI are set to 0. The toolbox offers several options to specify ROIs and create binary masks.

The toolbox supports a set of objects that you can use to create ROIs of many shapes, such circles, ellipses, polygons, rectangles, and hand-drawn shapes. After you create the objects, you can modify their shape, position, appearance, and behavior. For more information about the ROI shapes, see Create ROI Shapes.

Functions

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Represent ROIs as Geometric Shapes

`AssistedFreehand`	Assisted freehand region of interest
`Circle`	Circular region of interest
`Crosshair`	Crosshair region of interest
`Cuboid`	Cuboidal region of interest
`Ellipse`	Elliptical region of interest
`Freehand`	Freehand region of interest
`Line`	Line region of interest
`Point`	Point region of interest
`Polygon`	Polygonal region of interest
`Polyline`	Polyline region of interest
`Rectangle`	Rectangular region of interest

Create ROI Shapes

`drawassisted`	Create customizable freehand ROI with assistance from object edges
`drawcircle`	Create customizable circular ROI
`drawcrosshair`	Create customizable crosshair ROI
`drawcuboid`	Create customizable cuboidal ROI
`drawellipse`	Create customizable elliptical ROI
`drawfreehand`	Create customizable freehand ROI
`drawline`	Create customizable linear ROI
`drawpoint`	Create customizable point ROI
`drawpolygon`	Create customizable polygonal ROI
`drawpolyline`	Create customizable polyline ROI
`drawrectangle`	Create customizable rectangular ROI

Customize ROI Shapes

`draw`	Begin drawing ROI interactively
`reduce`	Reduce density of points in ROI
`beginDrawingFromPoint`	Begin drawing ROI from specified point
`inROI`	Query if points are located in ROI
`bringToFront`	Bring ROI to front of Axes stacking order
`wait`	Block MATLAB command line until ROI operation is finished

Create Mask from ROI

`createMask`	Create binary mask image from ROI
`roipoly`	Specify polygonal region of interest (ROI)
`poly2mask`	Convert region of interest (ROI) polygon to region mask

Filter Image Using ROI

`regionfill`	Fill specified regions in image using inward interpolation
`inpaintCoherent`	Restore specific image regions using coherence transport based image inpainting
`inpaintExemplar`	Restore specific image regions using exemplar-based image inpainting
`roicolor`	Select region of interest (ROI) based on color
`roifilt2`	Filter region of interest (ROI) in image
`reducepoly`	Reduce density of points in ROI using Ramer–Douglas–Peucker algorithm

Topics

Specify ROIs

Specify ROI as Binary Mask
You can create a binary mask by selecting pixels based on intensity values or position, or by using binary segmentation techniques.
Create ROI Shapes
ROI objects represent ROIs as geometric and hand-drawn shapes.
Create Binary Mask Using an ROI Function
This example shows to create a binary mask using one of the ROI creation functions, such as drawcircle, with the mask creation function createMask.
Classify Pixels That Are Partially Enclosed by ROI
Learn how many Image Processing Toolbox™ functions classify pixels that are only partially within the boundaries of a region of interest.

Filter ROIs

Overview of ROI Filtering
To filter a region of interest (ROI), first define a mask to separate the ROI from the background, then apply the filter to the ROI only.
Sharpen Region of Interest in an Image
This example shows how to use masked filtering to increase the sharpness of a specific region of interest.
Apply Custom Filter to Region of Interest in Image
This example shows how to define your own function and mask to filter a region of interest.
Fill Region of Interest in an Image
The process of filling a region of interest involves replacing all pixels in the region by interpolating inward from the boundary of the region.

Create Interactive ROIs Using Events and Callback Functions

Subsample or Simplify a Freehand ROI
This example shows how to subsample or reduce the number of points in a Freehand ROI object.
Rotate Image Interactively Using Rectangle ROI
This example shows how to rotate an image by using a Rectangle ROI with a callback function that calls imrotate when you move the ROI.
Use Polyline to Create Angle Measurement Tool
This example shows how to create an interactive tool that displays the angle between three vertices in a polyline ROI.
Measure Distances in an Image
This example shows how to use line ROIs to measure distances in an image.
Use Wait Function After Drawing ROI
This example shows how to define a custom wait function that blocks the MATLAB® command line until you finish positioning a rectangle.

Featured Examples

Use Freehand ROIs to Refine Segmentation Masks

Refine a logical segmentation mask by converting it into a Freehand ROI object. In this method, you take advantage of the interactive reshaping capability of the Freehand ROI object to make a better fit of the edge of the segmentation mask to the shape of the image region that you want to segment.

Open Live Script

Create Image Comparison Tool Using ROIs

Use the new ROI functions to create an interactive image comparison tool. When working with images, we often need to assess visually the impact a function has on an image. Some effects are clearly distinguishable, like an edge filter. But some impacts are more subtle and need closer inspection.

Open Script

Create Freehand ROI Editing Tool

Create a simple tool to edit the shape of a freehand ROI using another ROI object. By default, Freehand ROI objects include waypoints that you can click and drag to adjust the shape of the ROI. You can also add waypoints interactively to any part of the boundary.

Open Script

Interactive Image Inpainting Using Exemplar Matching

Interactively select image regions and inpaint the selected regions by using the exemplar based-matching method. Interactive inpainting allows you to select a region multiple times and perform inpainting iteratively to achieve the desired results.

Open Live Script