Learn more about Video and Image Processing Blockset

Draw Markers - Draw markers by embedding predefined shapes on output image

Library

Text & Graphics

Description

The Draw Markers block can draw multiple circles, x-marks, plus signs, stars, or squares on images by overwriting pixel values. Overwriting the pixel values embeds the shapes.

This block uses Bresenham's circle drawing algorithm to draw circles and Bresenham's line drawing algorithm to draw all other markers.

Port	Input/Output	Supported Data Types	Complex Values Supported
Image	M-by-N matrix of intensity values or an M-by-N-by-P color values where P is the number of color planes	Double-precision floating point Single-precision floating point Fixed point Boolean 8-, 16-, and 32-bit signed integer 8-, 16-, and 32-bit unsigned integer	No
R, G, B	Scalar, vector, or matrix that represents one plane of the input RGB video stream. Inputs to the R, G, and B ports must have the same dimensions and data type.	Same as Image port	No
Pts	2-by-N matrix of row and column pairs, where N is the total number of markers and each row and column pair defines the center of a marker.	Double-precision floating point Single-precision floating point 8-, 16-, and 32-bit signed integer 8-, 16-, and 32-bit unsigned integer If the input to the Image port is an integer, fixed point, or boolean data type, the input to the Pts port must also be an integer data type.	No
ROI	Four-element vector of integers that define a rectangular area in which to draw the markers. The first two elements represent the zero-based row and column coordinates of the upper-left corner of the area. The second two elements represent the height and width of the area.	Double-precision floating point Single-precision floating point 8-, 16-, and 32-bit signed integer 8-, 16-, and 32-bit unsigned integer	No
Clr	P-element vector or P-by-N matrix where P is the number of color planes	Same as Image port	No
Output	Scalar, vector, or matrix of pixel values that contain the marker(s)	Same as Image port	No

The output signal is the same size and data type as the inputs to the Image, R, G, and B ports.

Use the Marker shape parameter to specify one of the following types of markers:

Circle
X-mark
Plus
Star
Square

Use the Marker size parameter to define the size of the marker, in pixels. Enter a scalar value, M, that defines a (2M+1)-by-(2M+1) pixel square into which the marker fits. M must be greater than or equal to 1.

If, for the Marker shape parameter, you select:

Circle, X-mark, or Star

and you then select the,

Use antialiasing check box

the block performs a smoothing algorithm. The Draw Markers block uses an algorithm similar to the poly2mask function to determine which subpixels to draw.

Use the Draw markers in parameter to define one of the following types of areas in which to draw the markers.

Entire image, enables you to draw markers in the entire image.
Specify region of interest via port, the ROI port appears on the block. Enter a four-element vector of integer values, [r c height width], where r and c are the row and column coordinates of the upper-left corner of the area, and height and width represent the height (in rows) and width (in columns) of the area. If you specify values that are outside the image, the block clips the values to the image boundaries.

Use the Image signal parameter to specify one of the following ways to input and output a color video signal.

One multidimensional signal, the block accepts an M-by-N-by-P color video signal, where P is the number of color planes, at one port.
Separate color signals, additional ports appear on the block. Each port accepts one M-by-N plane of an RGB video stream.

Selecting Marker Fill and Border Colors

You can set the marker fill or border color via the input port or via the input dialog. Use the color input or color parameter to determine the appearance of the rectangle(s), line(s), polygon(s), or circle(s).

Fill Color

If you select the Filled check box, the Fill color source, Fill color and Opacity factor (between 0 and 1) parameters appear in the dialog box. Use the Fill color source parameter to specify either Input port or Specify via dialog for the color source. If Specify via dialog is selected, you can specify either Black, White, or User-specified value for the Fill color parameter for the shading inside the shape. The Color value(s) parameter is applicable when the User-specified value is selected. Use the Opacity factor (between 0 and 1) parameter to specify the opacity of the shading inside the shape, where 0 is transparent and 1 is opaque.

Border Color

If the Filled check box is not selected, the Border color source, and Border color parameters are available. Use the Border color source parameter to specify either Input port or Specify via dialog for the color source. If Specify via dialog is selected, you can specify either Black, White, or User-specified value for the Border color parameter. If the color is user specified, the Color value(s) parameter is used to enter the color.

Color Values

The following table describes what to enter for the Color Value(s) parameter based on the block input and the number of markers you are drawing. This parameter is applicable when User-specified value is selected for the border color source.

Block Input	Color Value(s) for Drawing One Marker or Multiple Markers with the Same Color	Color Value(s) for Drawing Multiple Markers with Unique Color
Intensity image	Scalar intensity value	R-element vector where R is the number of markers
Color image	P-element vector where P is the number of color planes	P-by-R matrix where P is the number of color planes and R is the number of markers

For each value in the parameter, enter a number between the minimum and maximum values that can be represented by the data type of the input image. If you enter a value outside this range, the block produces an error message.

Opacity Factor

The following table describes what to enter for the Opacity factor(s) (between 0 and 1) parameter based on the block input and the number of markers you are drawing. This parameter is applicable when the Filled check box is selected.

Opacity Factor value for Drawing One Marker or Multiple Markers with the Same Color	Oopacity Factor value for Drawing Multiple Marker with Unique Color
Scalar intensity value	R-element vector where R is the number of markers

Dialog Box

The Draw Markers dialog box appears as shown in the following figure.

Marker shape: Specify the type of marker(s) to draw. Your choices are Circle, X-mark, Plus, Star, or Square.
Marker size: Enter a scalar value that represents the size of the marker, in pixels.
Filled: Select this check box to fill the marker with an intensity value or a color. This parameter is visible if, for the Marker shape parameter, you choose Circle or Square.
Fill color source: Specify source for fill color value to either Specify via dialog or Input port. This parameter is visible if you select the Filled check box.
Fill color: If you select Black, the marker is black. If you select White, the marker is white. If you select User-specified value, the Color value(s) parameter appears in the dialog box. This parameter is visible if you select the Filled check box.
Border color source: Specify source for the border color value to either Specify via dialog or Input port. Border color options are visible when the fill shapes options are not selected. This parameter is visible if you select the Filled check box.
Border color: Specify the appearance of the shape's border. If you select Black, the border is black. If you select White, the border is white. If you select User-specified value, the Color value(s) parameter appears in the dialog box. This parameter is visible if you clear the Fill shapes check box.
Color value(s): Specify an intensity or color value for the marker's border or fill. This parameter is visible if, for the Border color or Fill color parameter, you select User-specified value. Tunable.
Opacity factor (between 0 and 1): Specify the opacity of the shading inside the marker, where 0 is transparent and 1 is opaque. This parameter is visible if you select the Filled check box. This parameter is tunable.
Draw markers in: Define the area in which to draw the markers. If you select Entire image, you can draw markers in the entire image. If you select Specify region of interest via port, the ROI port appears on the block. Enter a four-element vector, [r c height width], where r and c are the row and column coordinates of the upper-left corner of the area, and height and width represent the height (in rows) and width (in columns) of the area.
Use antialiasing: Perform a smoothing algorithm on the marker. This parameter is visible if, for the Marker shape parameter, you select Circle, X-mark, or Star.
Image signal: Specify how to input and output a color video signal. If you select One multidimensional signal, the block accepts an M-by-N-by-P color video signal, where P is the number of color planes, at one port. If you select Separate color signals, additional ports appear on the block. Each port accepts one M-by-N plane of an RGB video stream.

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