Read Image

Extract image from ROS 2 Image message

Since R2021b

• 

Libraries:
ROS Toolbox / ROS 2

Description

The Read Image block extracts an image from a ROS 2 sensor_msgs/Image or sensor_msgs/CompressedImage message. You can select the message parameters of a topic active on a live ROS 2 network, or specify the message parameters separately. The ROS 2 messages are specified as a nonvirtual bus. Use the Subscribe block output to receive a message from a ROS 2 network and input the message to the Read Image block.

Note

When reading ROS 2 image messages from the network, the Data property of the message can exceed the maximum array length set in Simulink^®. Follow the steps below to increase the maximum array length for all message types in the model:

1. Enable ROS options by selecting the Robot Operating System (ROS) app under the Apps tab and configure the ROS network parameters appropriately.

2. From the Prepare section under Simulation tab, select ROS Toolbox > Variable Size Messages.

3. Uncheck Use default limits for this message type and then in the Maximum length column, increase the length based on the number of pixels in the image.

Examples

Read ROS 2 Image Messages in Simulink® and Perform Registration using Feature Matching

Read ROS 2 sensor_msgs/Image messages in Simulink and perform image registration using feature matching.

• Open Live Script

Ports

Input

Msg — ROS 2 sensor_msgs/Image or sensor_msgs/CompressedImage message

nonvirtual bus

ROS 2 sensor_msgs/Image or sensor_msgs/CompressedImage message, specified as a nonvirtual bus. You can use the Subscribe block to get a message from an active ROS 2 network.

Data Types: bus

Output

Image — Extracted image signal

M-by-N-by-3 matrix | M-by-N matrix

Extracted image signal from a ROS 2 message, returned as an M-by-N-by-3 matrix for color images, and an M-by-N matrix for grayscale images. The matrix contains the pixel data from the Data property of the ROS 2 message.

Data Types: single | double | int8 | int16 | int32 | uint8 | uint16

AlphaChannel — Alpha channel for image

M-by-N matrix

Alpha channel for image, returned as an M-by-N matrix. This matrix is the same height and width as the image output. Each element has a value in the range [0,1] that indicates the opacity of the corresponding pixel, with a value of 0 being completely transparent.

Note

For CompressedImage messages, the alpha channel returns all zeros if the Show Alpha output port is enabled.

Dependencies

Enable Show Alpha output port parameter.

Data Types: single | double | int8 | int16 | int32 | uint8 | uint16

ErrorCode — Error code for image conversion

scalar

Error code for image conversion, returned as a scalar. The error code values are:

• 0 — Successfully converted the image message.

• 1 — Incorrect image encoding. Check that the incoming message encoding matches the Image Encoding parameter.

• 2 — The dimensions of the image message exceed the limits specified in the Maximum Image Size parameter.

• 3 — The Data field of the image message was truncated. See Manage Array Sizes for ROS Messages in Simulink to increase the maximum length of the array.

• 4 — Image decompression failed.

Data Types: uint8

Parameters

Maximum image size — Maximum image size

[2000 2000] (default) | two-element vector

Maximum image size, specified as a two-element [height width] vector.

Select Configure using ROS 2... to set this parameter automatically using an active topic on a ROS 2 network. You must be connected to the ROS 2 network.

Image encoding — Image encoding

rgb8 (default) | rgba8 | ...

Image encoding for the input ImageMsg. Select the encoding type that matches the Encoding property of the message. For more information about encoding types, see rosReadImage.

Show Alpha output port — AlphaChannel port toggle

off (default) | on

Toggle alpha channel output port on or off, if the selected encoding type supports alpha channels.

Dependencies

To enable this parameter, set the Image Encoding parameter to an encoding type that supports alpha channels.

Show ErrorCode output port — Toggle ErrorCode port

on (default) | off

Toggle the ErrorCode port on or off, to monitor errors.

Output variable-size signals — Variable-size signal output toggle

off (default) | on

Toggle whether to output a variable-size signal. Use variable-sized signals only if you expect the image size to change over time. For more information about variable-size signals, see Variable-Size Signal Basics (Simulink).

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using Simulink® Coder™.

Usage notes and limitations:

• Code generation and deployment of models involving sensor_msgs/CompressedImage message workflows requires a valid version of OpenCV and cv_bridge packages to be installed.

  For code generation and deployment of models involving sensor_msgs/Image message workflows, installation of OpenCV and cv_bridge are not required.

• Local host deployment is not supported for models involving sensor_msgs/CompressedImage message workflows.

Version History

Introduced in R2021b