Crosshair

Crosshair region of interest

Description

A Crosshair object specifies the position of a crosshair region-of-interest (ROI). You can customize the appearance and interactive behavior of the ROI.

For more information about using this ROI, including keyboard shortcuts, see Tips.

Creation

There are two ways to create a Crosshair object. For more information, see Create ROI Shapes.

• Use the drawcrosshair function. Use this function when you want to create the ROI and set the appearance in a single command. You can specify the position of the ROI interactively by drawing the ROI over an image using the mouse, or programmatically by using name-value arguments.

• Use the images.roi.Crosshair function described here. Use this function when you want to specify the appearance and behavior of the ROI before you specify the position of the ROI. After creating the object, you can specify the position interactively by using the draw function or programmatically by modifying properties of the object.

Syntax

roi = images.roi.Crosshair

roi = images.roi.Crosshair(ax)

roi = images.roi.Crosshair(___,PropertyName=Value)

Description

roi = images.roi.Crosshair creates a Crosshair object with default properties.

roi = images.roi.Crosshair(ax) creates the ROI in the axes specified by ax.

roi = images.roi.Crosshair(___,PropertyName=Value) sets properties of the ROI using one or more name-value arguments.

Example: images.roi.Crosshair(Color="y") creates a yellow colored Crosshair object.

Input Arguments

ax — Parent of ROI

gca (default) | Axes object | UIAxes object

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

Properties

Shape and Position

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 the x- and y-coordinates of the location where the horizontal line crosses the vertical line in the crosshair ROI. This value changes automatically when you draw or move the ROI.

Color and Styling

Color — ROI color

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

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

For a custom color, specify an RGB triplet or a hexadecimal color code.

• An RGB triplet is a three-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], for example, [0.4 0.6 0.7].

• A hexadecimal color code is a string scalar or character vector that starts with a hash symbol (#) followed by three or six hexadecimal digits, which can range from 0 to F. The values are not case sensitive. Therefore, the color codes "#FF8800", "#ff8800", "#F80", and "#f80" are equivalent.

Alternatively, you can specify some common colors by name. This table lists the named color options, the equivalent RGB triplets, and the hexadecimal color codes.

Color Name	Short Name	RGB Triplet	Hexadecimal Color Code	Appearance
"red"	"r"	[1 0 0]	"#FF0000"
"green"	"g"	[0 1 0]	"#00FF00"
"blue"	"b"	[0 0 1]	"#0000FF"
"cyan"	"c"	[0 1 1]	"#00FFFF"
"magenta"	"m"	[1 0 1]	"#FF00FF"
"yellow"	"y"	[1 1 0]	"#FFFF00"
"black"	"k"	[0 0 0]	"#000000"
"white"	"w"	[1 1 1]	"#FFFFFF"

This table lists the default color palettes for plots in the light and dark themes.

Palette	Palette Colors
"gem" — Light theme default Before R2025a: Most plots use these colors by default.
"glow" — Dark theme default

You can get the RGB triplets and hexadecimal color codes for these palettes using the orderedcolors and rgb2hex functions. For example, get the RGB triplets for the "gem" palette and convert them to hexadecimal color codes.

RGB = orderedcolors("gem");
H = rgb2hex(RGB);

Before R2023b: Get the RGB triplets using RGB = get(groot,"FactoryAxesColorOrder").

Example: Color="r"

Example: Color="green"

Example: Color=[0 0.4470 0.7410]

Example: Color="#00FFFF"

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.

SelectedColor — Color of ROI when selected

"none" (default) | RGB triplet | hexadecimal color code | color name | short color name

Color of the ROI when selected, specified as an RGB triplet, a hexadecimal color code, 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.

For a custom color, specify an RGB triplet or a hexadecimal color code.

• An RGB triplet is a three-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], for example, [0.4 0.6 0.7].

• A hexadecimal color code is a string scalar or character vector that starts with a hash symbol (#) followed by three or six hexadecimal digits, which can range from 0 to F. The values are not case sensitive. Therefore, the color codes "#FF8800", "#ff8800", "#F80", and "#f80" are equivalent.

Alternatively, you can specify some common colors by name. This table lists the named color options, the equivalent RGB triplets, and the hexadecimal color codes.

Color Name	Short Name	RGB Triplet	Hexadecimal Color Code	Appearance
"red"	"r"	[1 0 0]	"#FF0000"
"green"	"g"	[0 1 0]	"#00FF00"
"blue"	"b"	[0 0 1]	"#0000FF"
"cyan"	"c"	[0 1 1]	"#00FFFF"
"magenta"	"m"	[1 0 1]	"#FF00FF"
"yellow"	"y"	[1 1 0]	"#FFFF00"
"black"	"k"	[0 0 0]	"#000000"
"white"	"w"	[1 1 1]	"#FFFFFF"

This table lists the default color palettes for plots in the light and dark themes.

Palette	Palette Colors
"gem" — Light theme default Before R2025a: Most plots use these colors by default.
"glow" — Dark theme default

You can get the RGB triplets and hexadecimal color codes for these palettes using the orderedcolors and rgb2hex functions. For example, get the RGB triplets for the "gem" palette and convert them to hexadecimal color codes.

RGB = orderedcolors("gem");
H = rgb2hex(RGB);

Before R2023b: Get the RGB triplets using RGB = get(groot,"FactoryAxesColorOrder").

Example: SelectedColor="r"

Example: SelectedColor="green"

Example: SelectedColor=[0 0.4470 0.7410]

Example: SelectedColor="#00FFFF"

StripeColor — Color of ROI stripe

"none" (default) | RGB triplet | hexadecimal color code | color name | short color name

Color of the ROI stripe, specified as an RGB triplet, a hexadecimal color code, 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.

For a custom color, specify an RGB triplet or a hexadecimal color code.

• An RGB triplet is a three-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], for example, [0.4 0.6 0.7].

• A hexadecimal color code is a string scalar or character vector that starts with a hash symbol (#) followed by three or six hexadecimal digits, which can range from 0 to F. The values are not case sensitive. Therefore, the color codes "#FF8800", "#ff8800", "#F80", and "#f80" are equivalent.

Alternatively, you can specify some common colors by name. This table lists the named color options, the equivalent RGB triplets, and the hexadecimal color codes.

Color Name	Short Name	RGB Triplet	Hexadecimal Color Code	Appearance
"red"	"r"	[1 0 0]	"#FF0000"
"green"	"g"	[0 1 0]	"#00FF00"
"blue"	"b"	[0 0 1]	"#0000FF"
"cyan"	"c"	[0 1 1]	"#00FFFF"
"magenta"	"m"	[1 0 1]	"#FF00FF"
"yellow"	"y"	[1 1 0]	"#FFFF00"
"black"	"k"	[0 0 0]	"#000000"
"white"	"w"	[1 1 1]	"#FFFFFF"

This table lists the default color palettes for plots in the light and dark themes.

Palette	Palette Colors
"gem" — Light theme default Before R2025a: Most plots use these colors by default.
"glow" — Dark theme default

You can get the RGB triplets and hexadecimal color codes for these palettes using the orderedcolors and rgb2hex functions. For example, get the RGB triplets for the "gem" palette and convert them to hexadecimal color codes.

RGB = orderedcolors("gem");
H = rgb2hex(RGB);

Before R2023b: Get the RGB triplets using RGB = get(groot,"FactoryAxesColorOrder").

Example: StripeColor="r"

Example: StripeColor="green"

Example: StripeColor=[0 0.4470 0.7410]

Example: StripeColor="#00FFFF"

Visible — ROI visibility

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

ROI visibility, specified as "on" or "off", or as a numeric or logical 0 (false) or 1 (true). 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 can still access the properties of an invisible ROI.

Labels

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 | hexadecimal color code | color name | short color name

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

For a custom color, specify an RGB triplet or a hexadecimal color code.

• An RGB triplet is a three-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], for example, [0.4 0.6 0.7].

• A hexadecimal color code is a string scalar or character vector that starts with a hash symbol (#) followed by three or six hexadecimal digits, which can range from 0 to F. The values are not case sensitive. Therefore, the color codes "#FF8800", "#ff8800", "#F80", and "#f80" are equivalent.

Alternatively, you can specify some common colors by name. This table lists the named color options, the equivalent RGB triplets, and the hexadecimal color codes.

Color Name	Short Name	RGB Triplet	Hexadecimal Color Code	Appearance
"red"	"r"	[1 0 0]	"#FF0000"
"green"	"g"	[0 1 0]	"#00FF00"
"blue"	"b"	[0 0 1]	"#0000FF"
"cyan"	"c"	[0 1 1]	"#00FFFF"
"magenta"	"m"	[1 0 1]	"#FF00FF"
"yellow"	"y"	[1 1 0]	"#FFFF00"
"black"	"k"	[0 0 0]	"#000000"
"white"	"w"	[1 1 1]	"#FFFFFF"

This table lists the default color palettes for plots in the light and dark themes.

Palette	Palette Colors
"gem" — Light theme default Before R2025a: Most plots use these colors by default.
"glow" — Dark theme default

You can get the RGB triplets and hexadecimal color codes for these palettes using the orderedcolors and rgb2hex functions. For example, get the RGB triplets for the "gem" palette and convert them to hexadecimal color codes.

RGB = orderedcolors("gem");
H = rgb2hex(RGB);

Before R2023b: Get the RGB triplets using RGB = get(groot,"FactoryAxesColorOrder").

Example: LabelTextColor="r"

Example: LabelTextColor="green"

Example: LabelTextColor=[0 0.4470 0.7410]

Example: LabelTextColor="#00FFFF"

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.

Interactivity

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.

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.

Selected — Selection state of ROI

false, 0, or "off" (default) | true, 1, or "on"

Selection state of the ROI, specified as "off" or "on", or as a numeric or logical 0 (false) or 1 (true). A value of "off" is equivalent to false, and "on" is equivalent to true.

You can also set this property interactively. For example, clicking on the ROI selects the ROI and sets this property to true. Similarly, pressing the Ctrl key and clicking the ROI deselects the ROI and sets the value of this property to false.

Parent/Child

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.

Parent — ROI parent

Axes object | UIAxes object

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

Identifiers

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 Crosshair object does not use this data.

Object Functions

addlistener	Create event listener bound to event source
beginDrawingFromPoint	Begin drawing ROI from specified point
bringToFront	Bring ROI to front of Axes stacking order
draw	Begin drawing ROI interactively
wait	Block MATLAB command line until ROI operation is finished

Examples

Create Crosshair ROI

Read an image into the workspace and display it.

I = imread('baby.jpg');
figure;
imshow(I)

Place a crosshair ROI on the image programmatically. When you specify the position of the ROI, you must specify the axes.

h = images.roi.Crosshair(gca,'Position',[100,100]);

Create Crosshair Tool to Check Pixel Values

Read an image into the workspace.

img = imread("coins.png");

Display the image in a figure.

figure
hAx = gca;
imObj = imshow(img,Parent=hAx);
imObj.Parent.Visible = "on";

Create a crosshair ROI associated with the image. The crosshair does not have a position yet and therefore does not display on the image.

h = images.roi.Crosshair(Parent=hAx,LineWidth=1,Color="y");

Set up a listener to get notification when the ROI moves over the image. Because the code displays the value of the pixel under the crosshair, you must pass the image as an argument to the listener.

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

Begin drawing the ROI interactively. After you place the crosshair, you can then drag the crosshair to a new position. The title of the figure updates with the value of the pixel under the center of the crosshair.

draw(h)

This figure shows a sample appearance of the image with title during interactive movement of the crosshair ROI.

Define the displayInfo function called by the listener when a MovingROI event occurs.

function displayInfo(~,data,hAx,img)
    pos = ceil(data.CurrentPosition);
    title(hAx,"Pixel Value: "+num2str(img(pos(2),pos(1))))
end

More About

Events

To receive notification from the ROI when certain events happen, set up listeners for these events. You can specify a callback function that executes when one of these events occurs. When the ROI notifies your application through the listener, it returns data specific to the event. Look at the event class for the specific event to see what is returned.

For an example of using event listeners, see Create Crosshair Tool to Check Pixel Values.

Event Name	Trigger	Event Data	Event Attributes
DeletingROI	ROI is about to be interactively deleted.	event.EventData	NotifyAccess: private ListenAccess: public
DrawingStarted	ROI is about to be interactively drawn.	event.EventData	NotifyAccess: private ListenAccess: public
DrawingFinished	ROI has been interactively drawn.	event.EventData	NotifyAccess: private ListenAccess: public
MovingROI	ROI shape or location is being interactively changed.	images.roi.ROIMovingEventData	NotifyAccess: private ListenAccess: public
ROIMoved	ROI shape or location has been interactively changed.	images.roi.ROIMovingEventData	NotifyAccess: private ListenAccess: public
ROIClicked	ROI has been clicked.	images.roi.ROIClickedEventData	NotifyAccess: private ListenAccess: public

Tips

• To draw the ROI interactively using the draw or drawcrosshair function, position the cursor over the image and click the mouse to draw the ROI.

• The ROI supports the following interactivity, including keyboard shortcuts.

  Task	Description
  Cancel drawing operation.	Press Esc. The function returns a valid ROI object with an empty Position property.
  Move the ROI.	Position the cursor over the center of the crosshair ROI (where the two lines cross) and click and drag the crosshair. Another way to move the crosshair ROI is to position the cursor anywhere on one of the two lines and click. The other line in the crosshair jumps to the new crosshair center position.
  Delete the ROI.	Position the cursor over the ROI, right-click, and then choose Delete Crosshair from the context menu. You can also delete the ROI programmatically by using the delete function.

• For information about using an ROI in an app created with App Designer, see Using ROIs in Apps Created with App Designer.

Version History

Introduced in R2019b

R2026a: Specify colors using hexadecimal color codes

You can now specify colors, such as the Color, LabelTextColor, SelectedColor, and StripeColor properties, using hexadecimal color codes.

R2020a: UIContextMenu property is not recommended

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

There are no plans to remove support for the UIContextMenu property at this time.