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 video signal 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 I 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	Four-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
Output	Scalar, vector, or matrix of pixel values that contain the shape(s)	Same as I 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 the type of shape(s) to draw. Your choices are Rectangles, Lines, Polygons, or Circles.

If you clear the Fill shapes check box, the Border value parameter appears in the dialog box. Use this parameter determine the appearance of the rectangle(s), line(s), polygon(s), or circle(s). If you select Black, the border is black. If you select White, the border is white. If you select User-specified value, the Value(s) parameter appears in the dialog box. The following table describes what to enter for the Value(s) parameter based on the block input and the number of shapes you are drawing.

Block Input	Drawing One Shape	Drawing Multiple Shapes
Intensity image	Value(s) = Scalar intensity value	Value(s) = R-element vector where R is the number of shapes
Color image	Value(s) = P-element vector where P is the number of color planes	Value(s) = P-by-R matrix where P is the number of color planes and R is the number of shapes

For each value in the 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.

If you select the Fill shapes check box, the Fill value and Opacity factor (between 0 and 1) parameters appear in the dialog box. Use the Fill value parameter to specify the shading inside the shape. If you select Black, the shape is black. If you select White, the shape is white. If you select User-specified value, the Value(s) parameter appears in the dialog box. For a description of this parameter, see the preceding table. 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.

Use the Draw shapes in parameter to 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 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.

Use the Image signal parameter to 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.

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. See [1].

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.

If you select the Use antialiasing check box, the block applies an edge smoothing algorithm. See [1].

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.

If you select the Use antialiasing check box, the block applies an edge smoothing algorithm that is described next. First, the block calculates the distance from a point on the circle to the nearest pixel.

Then, it uses the following equations to calculate the intensity at pixels i and j:

In the previous equations, factor is the value you entered for the Opacity factor parameter. If you did not enter an opacity factor, the block sets it to 1. is the value you entered for the Border intensity parameter.

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 value: Specify the intensity of the shading inside the shape. This parameter is visible if you select the Fill shapes check box.
Border value: 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 Value(s) parameter appears in the dialog box. This parameter is visible if you clear the Fill shapes check box.
Value(s): Specify an intensity or color value for the shape's border or fill. This parameter is visible if, for the Border value or Fill value parameter, you select User-specified value. Tunable when Use antialiasing is turned off.
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.

References

[1] Gupta, S. and R.F. Sproull, "Filtering Edges for Gray-Scale Displays", Computer Graphics, Vol. 15, No. 3, August 1981.

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

Library

Description

Defining Shapes to Draw

Drawing Rectangles

Drawing Lines and Polylines

Drawing Polygons

Drawing Circles

Dialog Box

References

See Also