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. The toolbox supports a set of ROI objects that you can use to create ROIs of many shapes, such circles, ellipses, polygons, rectangles, and hand-drawn shapes. After creation, you can use ROI object properties to customize their appearance and functioning. In addition, the ROI objects support object functions and events that you can use to implement interactive behavior. For example, using events, your application can execute custom code whenever the ROI changes position. As a convenience, the toolbox includes a parallel set of convenience functions for ROI creation. For example, to create a rectangular ROI, you can use images.roi.Rectangle or the corresponding convenience function drawrectangle. For more information about ROIs, see ROI Creation Overview.

A common use of an ROI is to create 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. To create a mask, use the createMask object functions supported by most of the ROI objects. You can also create a mask without requiring an image using the poly2mask function.

Starting in R2018b, a new set of ROI objects replaced the previous set of ROI objects. The new objects provide better performance and more functional capabilities, such as face color transparency. With the new objects, you can also receive notification of interactions with the object, such as clicks or movement, using events. Although there are no plans to remove the old ROI objects at this time, switch to the new ROIs to take advantage of the additional capabilities and flexibility. For more information on migrating to the new ROIs, see ROI Migration.

Functions

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ROI Objects

`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
`draw`	Begin drawing ROI interactively

ROI Creation Convenience Functions

`drawassisted`	Create freehand ROI on image with assistance from image 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

ROI Object Customization

`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

Mask Creation

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

ROI Filtering

`regionfill`	Fill in 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

Create ROIs

ROI Creation Overview

You can create ROI objects that represent ROIs of various shapes, including circles, ellipses, polygons, lines, polylines, rectangles, and hand-drawn shapes.

ROI Migration

Starting in R2018b, a new set of ROI objects replaced the previous set of ROI objects.

Filter ROIs and Create Masks

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.

Create a Binary Mask

A binary mask classifies image pixels as belonging to either the region of interest or the background.

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.

Use Polyline to Create An Angle Measurement Tool

This example shows the steps need to create a three-point measurement tool using 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 capbility 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 the, inpaint the selected region by using 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