Have the semantics of ImageData coming from a depth camera changed between Gazebo7 and Gazebo8?

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We use a plugin to grab both the depth and image data from a depth sensor. However upon upgrading to Gazebo8 the code we were using to show the image information coming from the DepthCamera is now just blank gray all pixels at a value of about 128. Has something changed in the semantics DepthCamera->ImageData() in the change from Gazebo7 to Gazebo8?

I've tried changing the sensor type in the sdf from "depth" to "camera" leaving the rest of the settings the same and the image capture works. Not sure if this constitutes a bug or if I missed some errata.