## repository: https://code.ros.org/svn/ros-pkg

<<PackageHeader(compressed_image_transport)>>

<<TOC(3)>>

== Overview ==
`compressed_image_transport` is a plugin package for [[image_transport]]. It enables any node using `image_transport` classes to publish and subscribe to compressed image topics. Compression format (JPEG or PNG) and quality can be changed on the fly.

'''''Before reading this page, make sure you understand the [[image_transport]] package'''''

== Tutorials ==
See [[image_transport/Tutorials]] for general instruction on using `image_transport`. `compressed_image_transport` is featured in the `image_transport` tutorial [[image_transport/Tutorials/ExaminingImagePublisherSubscriber|Examining the Simple Image Publisher and Subscriber]].

== ROS API ==

{{{
#!clearsilver CS/NodeAPI
name = Publisher plugin
desc =
pub {
  0.name = <base_topic>/compressed
  0.type = sensor_msgs/CompressedImage
  0.desc = Compressed transport subtopic.
}
}}}

{{{{#!wiki version cturtle_and_older
{{{
#!clearsilver CS/NodeAPI
param {
group.0 {
  name=Searchable parameters
  desc=The plugin searches up the parameter tree starting from the `<base_topic>` namespace. For example, with topic `/image`, you could set parameter `/compressed_image_transport_jpeg_quality` to a global default, then override it for the specific topic by setting `/image/compressed_image_transport_jpeg_quality`.
  0.name = <base_topic>/compressed_image_transport_format
  0.type = string
  0.default = jpeg
  0.desc = Compression format to use, "jpeg" or "png".
  1.name = <base_topic>/compressed_image_transport_jpeg_quality
  1.type = int
  1.default = 80
  1.desc = JPEG quality percentile, in the range [1, 100]. Lower values trade image quality for space savings.
  2.name = <base_topic>/compressed_image_transport_png_level
  2.type = int
  2.default = 9
  2.desc = PNG compression level, in the range [1, 9]. Higher values trade computation time for space savings.
}
}
}}}

}}}}

{{{#!wiki version diamondback_and_newer
<<Include(compressed_image_transport/diamondback_params)>>
}}}

{{{
#!clearsilver CS/NodeAPI
name = Subscriber plugin
desc =
sub {
  0.name = <base_topic>/compressed
  0.type = sensor_msgs/CompressedImage
  0.desc = Compressed transport subtopic.
}
}}}

== Publishing compressed images directly ==
Some cameras (particularly webcams) output their image data already in JPEG format. When writing a driver for such a camera, a quick and dirty approach is to simply copy the JPEG data into a <<MsgLink(sensor_msgs/CompressedImage)>> message and publish it on a topic of the form `image_raw/compressed`. Then any ROS node using [[image_transport]] can subscribe to `image_raw` with transport `compressed`, just as if `image_transport` were used on the publisher side. Of course, the other transport topics (including `image_raw` itself) will not be available.

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