Learn more about Video and Image Processing Blockset

Draw Shapes - Draw rectangles, lines, polygons, or circles on images

Library

Text & Graphics

Description

The Draw Shapes block draws multiple rectangles, lines, polygons, or circles on images by overwriting pixel values. As a result, the shapes are embedded on the output image.

This block uses Bresenham's line drawing algorithm to draw lines, polygons, and rectangles. It uses Bresenham's circle drawing algorithm to draw circles.

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	Use integer values to define zero-based shape coordinates. If you enter noninteger values, the block rounds them to the nearest integer. For more information about how to specify shape coordinates for different shapes, see Defining Shapes to Draw.	Double-precision floating point (only supported if the input to the I or R, G, and B ports is floating point) Single-precision floating point (only supported if the input to the I or R, G, and B ports is floating point) 8-, 16-, and 32-bit signed integer 8-, 16-, and 32-bit unsigned integer	No
ROI	4-element vector of integers that defines a rectangular area in which to draw the shapes. 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 shape(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 Shape parameter to specify one of the following types type of shape(s) to draw.

Rectangles
Lines
Polygons
Circles

Use the Draw shapes in parameter to define one of the following types of area in which to draw the shapes.

Entire image, enables you to draw shapes 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, for the Shape parameter, you select:

Lines, Polygons, or Circles

and you then select the,

Use antialiasing check box,

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

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 Shape Fill and Border Colors

You can set the shape 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 Fill shapes 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.

Note If you are generating code and you select the Fill shapes check box, the word length of the block input(s) cannot exceed 16 bits.

Border Color

If the Fill shapes 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 shapes you are drawing.

Block Input	Color Value(s) for Drawing One Shape or Multiple Shapes with the Same Color	Color Value(s) for Drawing Multiple Shapes with Unique Color
Intensity image	Scalar intensity value	R-element vector where R is the number of shapes
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 shapes

For each value in the Color Value(s) 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 shapes you are drawing. This parameter is applicable when the Filled check box is selected.

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

Defining Shapes to Draw

This section explains how to use the Shape parameter and the Pts port to draw the following shapes:

Drawing Rectangles

The Draw Shapes block lets you draw one or more rectangles. Set the Shape parameter to Rectangles, and then follow the instructions in the table to specify the input to the Pts port to obtain the desired number of rectangles.

Shape Input to the Pts Port Drawn Shape

Single Rectangle

Shape	Input to the Pts Port	Drawn Shape
Single Rectangle	Four-element row or column vector `[r c height width]` where `r` and `c` are the zero-based row and column coordinates of the upper-left corner of the rectangle. `height` and `width` are the height, in pixels, and width, in pixels, of the rectangle. Here, `height` and `width` must be greater than 0.
N Rectangles	4-by-N matrix where each column of the matrix corresponds to a different rectangle and is of the same form as the vector for a single rectangle.

Four-element row or column vector
[r c height width] where

r and c are the zero-based row and column coordinates of the upper-left corner of the rectangle.
height and width are the height, in pixels, and width, in pixels, of the rectangle. Here, height and width must be greater than 0.

N Rectangles

4-by-N matrix

where each column of the matrix corresponds to a different rectangle and is of the same form as the vector for a single rectangle.

For an example of how to use the Draw Shapes block to draw a rectangle, see Tracking an Object Using Correlation.

Drawing Lines and Polylines

The Draw Shapes block lets you draw either a single line, or one or more polylines, where each polyline is a series of connected line segments. Set the Shape parameter to Lines, and then follow the instructions in the table to specify the input to the Pts port to obtain the desired shape.

Shape	Input to the Pts Port	Drawn Shape
Single Line	Four-element row or column vector `[r1 c1 r2 c2]` where `r1` and `c1` are the row and column coordinates of the beginning of the line. `r2` and `c2` are the row and column coordinates of the end of the line.
N Lines	4-by-N matrix where each column of the matrix corresponds to a different line and is of the same form as the vector for a single line.
Single Polyline with L-1 Segments	Vector of size 2L`[r1 c1 r2 c2 ... rL cL]` where `r1` and `c1` are the row and column coordinates of the beginning of the first line segment. `r2` and `c2` are the row and column coordinates of the end of the first line segment and the beginning of the second line segment `rL` and `cL` are the row and column coordinates of the end of the L-1^th line segment. The block produces an error message if the number of rows is less than two or is not a multiple of two.
N Polylines with the largest number of line segments in any line being L-1	2L-by-N matrix where each column of the matrix corresponds to a different polyline and is of the same form as the vector for a single polyline. If some polylines are shorter than others, repeat the ending coordinates to fill the polyline matrix. The block produces an error message if the number of rows is less than two or is not a multiple of two.

If you select the Use antialiasing check box, the block applies an edge smoothing algorithm.

For examples of how to use the Draw Shapes block to draw a line, see Finding Lines in Images and Measuring an Angle Between Lines.

Drawing Polygons

The Draw Shapes block lets you draw one or more polygons. Set the Shape parameter to Polygons, and then follow the instructions in the table to specify the input to the Pts port to obtain the desired number of polygons.

Shape Input to the Pts Port Drawn Shape

Single Polygon with L line segments

Shape	Input to the Pts Port	Drawn Shape
Single Polygon with L line segments	Row or column vector of size 2L `[r1 c1 r2 c2 ... rL cL]` where `r1` and `c1` are the row and column coordinates of the beginning of the first line segment. `r2` and `c2` are the row and column coordinates of the end of the first line segment and the beginning of the second line segment `rL` and `cL` are the row and column coordinates of the end of the L-1^th line segment and the beginning of the L^th line segment. The block connects `[r1 c1]` to `[rL cL]` to complete the polygon. The block produces an error if the number of rows is negative or not a multiple of two.
N Polygons with the largest number of line segments in any line being L	2L-by-N matrix where each column of the matrix corresponds to a different polygon and is of the same form as the vector for a single polygon. If some polygons are shorter than others, repeat the ending coordinates to fill the polygon matrix. The block produces an error message if the number of rows is less than two or is not a multiple of two.

Row or column vector of size 2L [r1 c1 r2 c2 ... rL cL] where

r1 and c1 are the row and column coordinates of the beginning of the first line segment.
r2 and c2 are the row and column coordinates of the end of the first line segment and the beginning of the second line segment
rL and cL are the row and column coordinates of the end of the L-1^th line segment and the beginning of the L^th line segment.

The block connects [r1 c1] to [rL cL] to complete the polygon. The block produces an error if the number of rows is negative or not a multiple of two.

N Polygons with the largest number of line segments in any line being L

2L-by-N matrix

where each column of the matrix corresponds to a different polygon and is of the same form as the vector for a single polygon. If some polygons are shorter than others, repeat the ending coordinates to fill the polygon matrix.

The block produces an error message if the number of rows is less than two or is not a multiple of two.

Drawing Circles

The Draw Shapes block lets you draw one or more circles. Set the Shape parameter to Circles, and then follow the instructions in the table to specify the input to the Pts port to obtain the desired number of circles.

Shape Input to the Pts Port Drawn Shape

Single Circle

Shape	Input to the Pts Port	Drawn Shape
Single Circle	Three-element row or column vector `[r c radius]` where `r` and `c` are the row and column coordinates of the center of the circle. `radius` is the radius of the circle, which must be greater than 0.
N Circles	3-by-N matrix where each column of the matrix corresponds to a different circle and is of the same form as the vector for a single circle.

Three-element row or column vector
[r c radius] where

r and c are the row and column coordinates of the center of the circle.
radius is the radius of the circle, which must be greater than 0.

N Circles

3-by-N matrix

where each column of the matrix corresponds to a different circle and is of the same form as the vector for a single circle.

Dialog Box

Shape: Specify the type of shape(s) to draw. Your choices are Rectangles, Lines, Polygons, or Circles.
Fill shapes: Fill the shape with an intensity value or a color.
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 Fill shapes check box.
Fill color: 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 select the Fill shapes 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 Fill shapes 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 shape's border or fill. This parameter is visible if, for the Border color or Fill color parameter, you select User-specified value. This parameter is tunable.
Opacity factor (between 0 and 1): Specify the opacity of the shading inside the shape, where 0 is transparent and 1 is opaque. This parameter is visible if you select the Fill shapes check box.
Draw shapes in: Define the area in which to draw the shapes. If you select Entire image, you can draw shapes 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 line, polygon, or circle. This parameter is visible if, for the Shape parameter, you select Lines, Polygons, or Circles.
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.

Draw Markers	Video and Image Processing Blockset software
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Draw Shapes - Draw rectangles, lines, polygons, or circles on images

Library

Description

Selecting Shape Fill and Border Colors

Fill Color

Border Color

Color Values

Opacity Factor

Defining Shapes to Draw

Drawing Rectangles

Drawing Lines and Polylines

Drawing Polygons

Drawing Circles

Dialog Box

See Also

Related Products & Applications