drawcrosshair

Create customizable crosshair ROI

Syntax

roi = drawcrosshair

roi = drawcrosshair(ax)

roi = drawcrosshair(___,Name,Value)

Description

The drawcrosshair function creates a Crosshair object that specifies the position of a crosshair region of interest (ROI). You can create the ROI interactively by drawing the ROI over an image using the mouse, or programmatically by using name-value arguments. You can also specify the initial appearance and behavior of the ROI.

After you create the ROI, you can use object properties, object functions, and event notifications to customize the shape, position, appearance, and behavior of the ROI. For more information about using these capabilities, see Tips.

roi = drawcrosshair creates a Crosshair object and enables interactive drawing of the ROI on the current axes. The crosshair ROI is made up of two perpendicular lines that are the full width and height of the axes.

To draw the ROI, move the cursor over the axes and click. For more information about using the ROI, including keyboard shortcuts and context menu options, see Tips.

roi = drawcrosshair(ax) begins interactive placement of an ROI in the axes specified by ax.

roi = drawcrosshair(___,Name,Value) customizes the appearance and behavior of the ROI using one or more name-value pairs. Unspecified name-value pairs are set to the default value.

Examples

Create Crosshair ROI and Modify ROI Properties

This example shows how to create a crosshair ROI both interactively and programmatically.

Create Crosshair ROI

Read an image into the workspace and display it.

figure;
imshow('pears.png')

Create a crosshair ROI on the image using the drawcrosshair function interactively. Move the cursor over the image anywhere and click to draw the ROI. Click on the ROI Center (the point where the horizontal line crosses the vertical line) to move the ROI on the image.

h = drawcrosshair();

Create Crosshair ROI Programmatically

Read an image into the workspace and display it.

figure;
imshow('pears.png')

Create a crosshair ROI on the image using the drawcrosshair function. Use Name/Value pair arguments to specify the initial position of the ROI.

h = drawcrosshair('Position',[100 100]);

Modify Crosshair ROI Appearance Using Properties

Read an image into the workspace and display it.

figure;
imshow('pears.png')

Create a crosshair ROI on the image using the drawcrosshair function. Use Name/Value pair arguments to specify the initial position of the ROI.

h = drawcrosshair('Position',[100 100]);

Use properties of the Crosshair object to change the lines in the ROI to be striped. The drawcrosshair function returns a Crosshair object that supports many properties. Use the StripeColor property to specify the stripe color.

h.StripeColor = 'green';

Display Value of Pixel Specified By Crosshair ROI

Read an image into the workspace and display it.

img = imread('coins.png');
hAx = gca;
imObj = imshow(img,'Parent',hAx);
imObj.Parent.Visible = 'on';

Create a crosshair ROI.

h = drawcrosshair('Parent',hAx,'Position',[50 50],'LineWidth',1,'Color','y');

Use the addlistener object function to receive notification when the ROI moves. Specify the callback function to execute when the event occurs. When you move the crosshair ROI, the code displays the position of the crosshair in the title and displays the pixel value at the location in the ROI label.

addlistener(h,'MovingROI',@(src,data)displayInfo(src,data,hAx,img));

This is the callback function that displays the value of the pixel specified by the crosshair ROI.

function displayInfo(src,data,hAx,img)
pos = ceil(data.CurrentPosition);
pixval = img(pos(2),pos(1));
src.Label = mat2str(pixval);
title(mat2str(pos));
end

Input Arguments

ax — Parent of ROI

gca (default) | Axes object | UIAxes object

Parent of ROI, specified as an Axes object or a UIAxes object. For information about using an ROI in a UIAxes, including important limitations, see Using ROIs in Apps Created with App Designer.

Name-Value Arguments

Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Before R2021a, use commas to separate each name and value, and enclose Name in quotes.

Example: 'Color','y' creates a yellow colored Crosshair object

Color — ROI color

[0 0.4470 0.7410] (default) | RGB triplet | color name | short color name

ROI color, specified as an RGB triplet, a color name, or a short color name.

You can specify any color using an RGB triplet. An RGB triplet is a 3-element row vector whose elements specify the intensities of the red, green, and blue components of the color. The intensities must be in the range [0,1].

You can specify some common colors by name as a string scalar or character vector. This table lists the named color options and the equivalent RGB triplets.

Color Name	Short Name	RGB Triplet	Appearance
'red'	'r'	[1 0 0]
'green'	'g'	[0 1 0]
'blue'	'b'	[0 0 1]
'cyan'	'c'	[0 1 1]
'magenta'	'm'	[1 0 1]
'yellow'	'y'	[1 1 0]
'black'	'k'	[0 0 0]
'white'	'w'	[1 1 1]

Here are the RGB triplets for the default colors that MATLAB^® uses in many types of plots.

RGB Triplet	Appearance
[0 0.4470 0.7410]
[0.8500 0.3250 0.0980]
[0.9290 0.6940 0.1250]
[0.4940 0.1840 0.5560]
[0.4660 0.6740 0.1880]
[0.3010 0.7450 0.9330]
[0.6350 0.0780 0.1840]

Example: 'Color','r'

Example: 'Color','green'

Example: 'Color',[0 0.4470 0.7410]

ContextMenu — Context menu

ContextMenu object

Context menu that displays when you right-click the ROI, specified as a ContextMenu object. You can create a custom context menu by using the uicontextmenu function and then configuring context menu properties.

Deletable — Context menu provides option to delete the ROI

true or 1 (default) | false or 0

Context menu provides an option to delete the ROI, specified as a numeric or logical 1 (true) or 0 (false). When the value is true, you can delete the ROI interactively using the context menu. When the value is false, the context menu option to delete the ROI is disabled.

In both cases, you can delete the ROI outside of the context menu by using the delete function.

DrawingArea — Area of axes in which you can interactively place ROI

'auto' (default) | 'unlimited' | [x,y,w,h]

Area of the axes in which you can interactively place the ROI, specified as one of the values in this table.

Value	Description
'auto'	The drawing area is the current axes limits (default).
'unlimited'	The drawing area has no boundary and ROIs can be drawn or dragged to extend beyond the axes limits.
[x,y,w,h]	The drawing area is restricted to a rectangular region beginning at (x,y), and extending to width w and height h.

HandleVisibility — Visibility of ROI handle in Children property of parent

'on' (default) | 'off' | 'callback'

Visibility of the ROI handle in the Children property of the parent, specified as one of the values in this table.

Value	Description
'on'	The object handle is always visible (default).
'off'	The object handle is hidden at all times.
'callback'	The object handle is visible from within callbacks or functions invoked by callbacks, but not from within functions invoked from the command line.

InteractionsAllowed — Interactivity of ROI

'all' (default) | 'none'

Interactivity of the ROI, specified as one of the values in this table.

Value	Description
'all'	The ROI is fully interactable.
'none'	The ROI is not interactable, and no drag points are visible.

Label — ROI label

'' (default) | character vector | string scalar

ROI label, specified as a character vector or string scalar. By default, the ROI has no label ('').

LabelAlpha — Transparency of text background

1 (default) | number in the range [0, 1]

Transparency of the text background, specified as a number in the range [0, 1]. When set to 1, the text background is completely opaque. When set to 0, the text background is completely transparent.

LabelTextColor — Label text color

'black' (default) | RGB triplet | color name | short color name

Label text color, specified as an RGB triplet, a color name, or a short color name.

You can specify any color using an RGB triplet. An RGB triplet is a 3-element row vector whose elements specify the intensities of the red, green, and blue components of the color. The intensities must be in the range [0,1].

You can specify some common colors by name as a string scalar or character vector. This table lists the named color options and the equivalent RGB triplets.

Color Name	Short Name	RGB Triplet	Appearance
'red'	'r'	[1 0 0]
'green'	'g'	[0 1 0]
'blue'	'b'	[0 0 1]
'cyan'	'c'	[0 1 1]
'magenta'	'm'	[1 0 1]
'yellow'	'y'	[1 1 0]
'black'	'k'	[0 0 0]
'white'	'w'	[1 1 1]

Here are the RGB triplets for the default colors that MATLAB uses in many types of plots.

RGB Triplet	Appearance
[0 0.4470 0.7410]
[0.8500 0.3250 0.0980]
[0.9290 0.6940 0.1250]
[0.4940 0.1840 0.5560]
[0.4660 0.6740 0.1880]
[0.3010 0.7450 0.9330]
[0.6350 0.0780 0.1840]

Example: 'LabelTextColor','r'

Example: 'LabelTextColor','green'

Example: 'LabelTextColor',[0 0.4470 0.7410]

LabelVisible — Label visibility

'on' (default) | 'off' | 'hover'

Label visibility, specified as one of these values.

Value	Description
'on'	Label is visible when the ROI is visible.
'hover'	Label is visible only when the mouse is hovering over the ROI.
'off'	Label is not visible.

LineWidth — Width of ROI border

positive number

Width of the ROI border, specified as a positive number in points. The default value is three times the number of points per screen pixel, such that the border is three pixels wide.

Parent — ROI parent

Axes object | UIAxes object

ROI parent, specified as an Axes or UIAxes object. For information about using an ROI in a UIAxes, including important limitations, see Using ROIs in Apps Created with App Designer.

Position — Position of ROI

1-by-2 numeric vector

Position of the ROI, specified as a 1-by-2 numeric vector of the form [x y]. The values x and y specify coordinates where the horizontal line crosses the vertical line in the crosshair ROI.

Selected — Selection state of ROI

false or 0 (default) | true or 1

Selection state of the ROI, specified as a numeric or logical 0 (false) or 1 (true).

SelectedColor — Color of ROI when selected

'none' (default) | RGB triplet | color name | short color name

Color of the ROI when selected, specified as an RGB triplet, a color name, a short color name, or 'none'. If you specify 'none', then the value of Color defines the color of the ROI for all states, selected or not.

You can specify any color using an RGB triplet. An RGB triplet is a 3-element row vector whose elements specify the intensities of the red, green, and blue components of the color. The intensities must be in the range [0,1].

You can specify some common colors by name as a string scalar or character vector. This table lists the named color options and the equivalent RGB triplets.

Color Name	Short Name	RGB Triplet	Appearance
'red'	'r'	[1 0 0]
'green'	'g'	[0 1 0]
'blue'	'b'	[0 0 1]
'cyan'	'c'	[0 1 1]
'magenta'	'm'	[1 0 1]
'yellow'	'y'	[1 1 0]
'black'	'k'	[0 0 0]
'white'	'w'	[1 1 1]

Here are the RGB triplets for the default colors that MATLAB uses in many types of plots.

RGB Triplet	Appearance
[0 0.4470 0.7410]
[0.8500 0.3250 0.0980]
[0.9290 0.6940 0.1250]
[0.4940 0.1840 0.5560]
[0.4660 0.6740 0.1880]
[0.3010 0.7450 0.9330]
[0.6350 0.0780 0.1840]

Example: 'SelectedColor','r'

Example: 'SelectedColor','green'

Example: 'SelectedColor',[0 0.4470 0.7410]

StripeColor — Color of ROI stripe

'none' (default) | RGB triplet | color name | short color name

Color of the ROI stripe, specified as an RGB triplet, a color name, a short color name, or 'none'. If you specify 'none', then the ROI edge is a solid color specified by Color. Otherwise, the edge of the ROI is striped, with colors alternating between the colors specified by Color and StripeColor.

You can specify any color using an RGB triplet. An RGB triplet is a 3-element row vector whose elements specify the intensities of the red, green, and blue components of the color. The intensities must be in the range [0,1].

You can specify some common colors by name as a string scalar or character vector. This table lists the named color options and the equivalent RGB triplets.

Color Name	Short Name	RGB Triplet	Appearance
'red'	'r'	[1 0 0]
'green'	'g'	[0 1 0]
'blue'	'b'	[0 0 1]
'cyan'	'c'	[0 1 1]
'magenta'	'm'	[1 0 1]
'yellow'	'y'	[1 1 0]
'black'	'k'	[0 0 0]
'white'	'w'	[1 1 1]

Here are the RGB triplets for the default colors that MATLAB uses in many types of plots.

RGB Triplet	Appearance
[0 0.4470 0.7410]
[0.8500 0.3250 0.0980]
[0.9290 0.6940 0.1250]
[0.4940 0.1840 0.5560]
[0.4660 0.6740 0.1880]
[0.3010 0.7450 0.9330]
[0.6350 0.0780 0.1840]

Example: 'StripeColor','r'

Example: 'StripeColor','green'

Example: 'StripeColor',[0 0.4470 0.7410]

Tag — Tag to associate with ROI

'' (default) | character vector | string scalar

Tag to associate with the ROI, specified as a character vector or string scalar. Use the tag value to find the ROI object in a hierarchy of objects using the findobj function.

UserData — Data to associate with ROI

any MATLAB data

Data to associate with the ROI, specified as any MATLAB data. For example, you can specify a scalar, vector, matrix, cell array, string, character array, table, or structure. The drawcrosshair object does not use this data.

Visible — ROI visibility

'on' (default) | 'off' | on/off logical value

ROI visibility, specified as 'on' or 'off', or as a numeric or logical 1 (true) or 0 (false). A value of 'on' is equivalent to true, and 'off' is equivalent to false. The value is stored as an on/off logical value of type OnOffSwitchState.

Value	Description
'on'	Display the ROI.
'off'	Hide the ROI without deleting it. You still can access the properties of an invisible ROI.

Output Arguments

roi — Crosshair ROI

Crosshair object

Crosshair ROI, returned as a Crosshair object.

Tips

• This table describes how to perform common tasks with a crosshair ROI.

  Task	Description
  Cancel the drawing operation.	Start drawing the ROI and press Esc before releasing the mouse. The function returns a valid ROI object with an empty Position property.
  Move the ROI.	Position the pointer over the ROI. The pointer changes to a fleur shape. Click and drag to move the ROI.
  Delete the ROI.	Position the pointer over the ROI and right-click to view its context menu. Select Delete Crosshair from the menu. You can also delete the ROI using the delete function.

• The drawcrosshair function creates a Crosshair object. After you create the object, you can modify the position, appearance, and behavior of the ROI by using these object capabilities.

  Capability	Support
  Object properties	ROI objects have properties that specify their shape, position, appearance, and behavior. After you create the ROI object, change properties using dot notation. For example, to change the color of the roi to yellow, set its Color property: roi.Color = 'yellow'
  Object functions	ROI objects have object functions that operate on the ROIs. For example, if you want to pause the MATLAB command line after creating an ROI, use the wait function.
  Event notifications	ROI objects can notify your code when certain events occur, such as when the ROI is clicked or when the ROI is being moved. To receive event notifications, set up listeners. When the ROI notifies your application through the listener, it returns data specific to the event. For example, with the ROIMoved event, the ROI object returns its previous position and its current position. You can specify a callback function that executes when an event occurs.

  For an example of using event listeners with the Crosshair object, see Display Value of Pixel Specified By Crosshair ROI.

Version History

Introduced in R2019b

R2020a: UIContextMenu name-value argument is not recommended

Not recommended starting in R2020a

Starting in R2020a, using the UIContextMenu name-value argument to assign a context menu to an ROI object is not recommended. Use the ContextMenu name-value argument instead. The values are the same.

There are no plans to remove support for the UIContextMenu name-value argument at this time.