Point
R2026bDescription
A Point object labels interactive points in a
Viewer object. The properties of the object control the appearance and
behavior of the point annotation.
Interactive viewer-based ROIs enable you to draw, edit, and
measure regions of interest on images and volumes displayed using imageshow
and volshow. Interactive ROIs support dragging, resizing, event callbacks,
and measurement labels. Use interactive viewer-based ROIs to manually annotate an image, build
annotation workflows in apps, or respond to user interactions with ROI shapes. For a comparison
of interactive viewer-based ROIs with other ROIs, see Choose Approach to Annotate ROIs in Images.
Creation
You can create a Point object in these ways. For more information, see
Create Interactive Viewer-Based ROIs.
Interactively draw a point in a
Viewerobject. From the viewer toolbar, select the draw annotations icon
, then select the draw point icon
. Click to place the point.To export the point to the workspace as a
Pointobject, right-click the point and select Export annotation to workspace.Use the
uidrawfunction to interactively draw the ROI in a specified viewer and create the ROI object.Use the
images.ui.graphics.roi.Pointfunction described here. After you create the ROI, you can display it by adding the object to theAnnotationsproperty of aViewerobject.
Description
p = images.ui.graphics.roi.Point creates a Point
object with default property values. Use p to query and modify
properties of the Point object after you create it.
p = images.ui.graphics.roi.Point(Name=Value)
Example:
images.ui.graphics.roi.Point(Position=[35 3 1012]) creates a point
annotation at the xyz-coordinates (35, 3, 1012).
Properties
Shape and Position
Position of the ROI, specified as a 2-element numeric vector of the form
[x y] or a 3-element numeric vector of the form [x y
z]. If you specify this values as a 2-element vector, the object sets the
z-coordinate of the point to 1. The object
always stores this property value as a 3-element vector.
Color and Styling
ROI color, specified as an RGB triplet, a hexadecimal color code, a color name, or a short color name.
These are the RGB triplets for the default colors used in 2-D and 3-D
Viewer scenes.
| RGB Triplet | Appearance | Default Use |
|---|---|---|
[0 0.5610 1] |
| This is the default color when creating an ROI in a 2-D
Viewer object from the toolbar or by using the
uidraw function. |
[0.8660 0.3290 0] |
| This is the default color when creating an ROI in a 3-D
Viewer object from the toolbar or by using
uidraw. This color is also the default when you
create an ROI in any Viewer object by using an object
constructor function such as
images.ui.graphics.roi.Circle. |
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 from0toF. 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 |
|---|---|
Before R2025a: Most plots use these colors by 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);Example: Color="r"
Example: Color="green"
Example: Color=[0 0.4470 0.7410]
Example: Color="#00FFFF"
ROI visibility, specified as "on" or "off", or as
. 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. |
ROI label, specified as a string scalar or character vector. By default, the label
shows the position of the point with no units. If the parent Viewer
has a nondefault value for the SpatialUnits property, such as
"mm", then the label includes the specified units.
To display a custom label, specify the label to display as a string scalar or
character vector. To display no label, specify the Label value as
"".
Interactivity
Interactivity of the ROI, specified as one of the values in this table.
| Value | Description |
|---|---|
"all" | You can fully interact with the ROI and translate (move) the ROI. |
"none" | You cannot interact with the ROI. No drag points are visible. |
"translate" | You can translate the ROI within the drawing area. |
"click" | You can click the ROI, but you cannot translate the ROI interactively.
After you click the ROI, the parent Viewer broadcasts the
AnnotationMoved event.
|
Identifiers
Tag to associate with the ROI, specified as a character vector or string scalar. This property has no effect on the display, and the viewer does not use this property. You can use this property to track annotations for app building.
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. This property has no effect on the display, and the viewer does not use this property. You can use this property to append metadata to the ROI for app building.
Object Functions
createMask | Create binary mask image from ROI |
Examples
Display an image in a Viewer object. The viewer v is the parent of the image object created by imageshow.
img = imageshow("pears.png");
v = img.Parent;Create a point ROI on the image, using the Position property to specify the position of the ROI.
position = [445 210]; p = images.ui.graphics.roi.Point(Position=position);
Display the ROI by adding it to the Annotations property of the Viewer object.
v.Annotations = [v.Annotations; p];
Create a new viewer window by displaying a 10-by-10-by-10 cube.
V = ones(10,10,10); vol = volshow(V);
Get a handle to the viewer window that contains the volume.
viewer = vol.Parent;
Create a point annotation object with default property values.
point1 = images.ui.graphics.roi.Point
point1 =
Point with properties:
Label: [0×0 string]
Color: [0.8500 0.3250 0.0980]
Position: [0 0 0]
Tag: ""
UserData: []
Create a point annotation with a custom position and label.
point2 = images.ui.graphics.roi.Point(Position=[1 10 10],Label="Point 2")point2 =
Point with properties:
Label: "Point 2"
Color: [0.8500 0.3250 0.0980]
Position: [1 10 10]
Tag: ""
UserData: []
Add the annotations to the viewer.
viewer.Annotations = [point1 point2];
To append spatial units to coordinate labels, update the SpatialUnits property of the viewer. By default, annotation labels do not display a unit.
viewer.SpatialUnits = "mm";
Tips
The
Pointobject supports these forms of interactivity.Behavior Interaction Add annotation From the viewer toolbar, select the draw annotations icon
, then select the draw point icon
. Click to place the point.Move annotation Drag the vertex of the annotation, not the label. Edit annotation label Right-click the vertex of the annotation, not the label. From the context menu, select Edit label. When the label text highlights, type new text for the label. To finish editing, click outside the label. Remove annotation Right-click the vertex of the annotation, not the label. From the context menu, select Remove annotation. Select Remove all annotations to remove all annotations in the viewer. When placing annotations, consider zooming in or, for 3-D viewers, snapping to an orthogonal view for greater spatial accuracy. Zoom in using the scroll wheel, or by selecting the zoom icon
from the viewer toolbar. Snap to an orthogonal view by
clicking the orientation axes labels in the lower-left corner of the viewer.
