readImage

Convert ROS image data into MATLAB image

Syntax

img = readImage(msg)

[img,alpha] = readImage(msg)

Description

img = readImage(msg) converts the raw image data in the message object, msg, into an image matrix, img. You can call readImage using either 'sensor_msgs/Image' or 'sensor_msgs/CompressedImage' messages.

ROS image message data is stored in a format that is not compatible with further image processing in MATLAB^®. Based on the specified encoding, this function converts the data into an appropriate MATLAB image and returns it in img.

[img,alpha] = readImage(msg) returns the alpha channel of the image in alpha. If the image does not have an alpha channel, then alpha is empty.

Examples

Read ROS Image Data

Load sample ROS messages including a ROS image message, img.

exampleHelperROSLoadMessages

Read the ROS image message as a MATLAB® image.

image = readImage(img);

Display the image.

imshow(image)

Input Arguments

msg — ROS image message

Image object handle | CompressedImage object handle

'sensor_msgs/Image' or 'sensor_msgs/CompressedImage' ROS image message, specified as an Image or Compressed Image object handle.

Output Arguments

img — Image

grayscale image matrix | RGB image matrix | m-by-n-by-3 array

Image, returned as a matrix representing a grayscale or RGB image or as an m-by-n-by-3 array, depending on the sensor image.

alpha — Alpha channel

uint8 grayscale image

Alpha channel, returned as a uint8 grayscale image. If no alpha channel exists, alpha is empty.

Note

For CompressedImage messages, you cannot output an Alpha channel.

Tips

ROS image messages can have different encodings. The encodings supported for images are different for 'sensor_msgs/Image' and 'sensor_msgs/CompressedImage' message types. Fewer compressed images are supported. The following encodings for raw images of size M-by-N are supported using the 'sensor_msgs/Image' message type ('sensor_msgs/CompressedImage' support is in bold):

• rgb8, rgba8, bgr8, bgra8: img is an rgb image of size M-by-N-by-3. The alpha channel is returned in alpha. Each value in the outputs is represented as a uint8.

• rgb16, rgba16, bgr16, and bgra16: img is an RGB image of size M-by-N-by-3. The alpha channel is returned in alpha. Each value in the output is represented as a uint16.

• mono8 images are returned as grayscale images of size M-by-N-by-1. Each pixel value is represented as a uint8.

• mono16 images are returned as grayscale images of size M-by-N-by-1. Each pixel value is represented as a uint16.

• 32fcX images are returned as floating-point images of size M-by-N-by-D, where D is 1, 2, 3, or 4. Each pixel value is represented as a single.

• 64fcX images are returned as floating-point images of size M-by-N-by-D, where D is 1, 2, 3, or 4. Each pixel value is represented as a double.

• 8ucX images are returned as matrices of size M-by-N-by-D, where D is 1, 2, 3, or 4. Each pixel value is represented as a uint8.

• 8scX images are returned as matrices of size M-by-N-by-D, where D is 1, 2, 3, or 4. Each pixel value is represented as a int8.

• 16ucX images are returned as matrices of size M-by-N-by-D, where D is 1, 2, 3, or 4. Each pixel value is represented as a int16.

• 16scX images are returned as matrices of size M-by-N-by-D, where D is 1, 2, 3, or 4. Each pixel value is represented as a int16.

• 32scX images are returned as matrices of size M-by-N-by-D, where D is 1, 2, 3, or 4. Each pixel value is represented as a int32.

• bayer_X images are returned as either Bayer matrices of size M-by-N-by-1, or as a converted image of size M-by-N-by-3 (Image Processing Toolbox™ is required).

The following encoding for raw images of size M-by-N is supported using the 'sensor_msgs/CompressedImage' message type:

• rgb8, rgba8, bgr8, and bgra8: img is an rgb image of size M-by-N-by-3. The alpha channel is returned in alpha. Each output value is represented as a uint8.