Thanks, Cedric. 
--Nick 

On Dec 6, 2010, at 8:26 AM, Cedric Pradalier wrote:

> Hi Nick,
> 
> As far as I know, the publish operation for image transport are in a "if 
> (numSubscriber() > 0) { ... publish ...} " block.
> If there is no subscriber, the serialisation code should  not be  called 
> at all, so the cost should be very close to 3.
> 
> On 12/06/10 17:19, Nicholas Butko wrote:
>> Does anyone familiar with the details of roscpp or imae_transport know, specifically in the context of no subscribers, (a) how much overhead is there to publish something? and (b) does that overhead scale with the size of the message?
>> 
>> Specifically I am interested in the case of images. Consider three cases:
>> 
>> 1) a node publishes an image, and it is shown in image_view
>> 2) a node publishes an image, but it is not shown in image_view or anywhere else
>> 3) a node does not publish an image
>> 
>> Clearly there will be a lot more computation associated with (1) than (3), but what about (2) -- is it closer to (1) or (3) or somewhere close to the middle?
>> 
>> --Nick
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>> 
> 
> -- 
> Dr. Cedric Pradalier
> http://www.asl.ethz.ch/people/cedricp
> 
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