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Streaming JPEG images via USB to a PDA

My assignment is to display JPEG images streamed to a PDA via USB at 10 frames per second or more.  Since Lab View does not provide a means of decoding JPEG data resident in memory (only files can be opened), I developed a DLL to decode the JPEG data.  The decoding of a 320x240 image takes <100 milliseconds.  Displaying that image by Draw Flattened Pixmap & "picture" requires ~400 milliseconds (?!?).  If a larger image is sent, the display time increases even though only 320x240 pixels are actually displayed.  I've attached a screenshot of the block diagram.
  • Is there an alternative to Draw Flattened Pixmap and "picture" that would be more efficient?
  • Why does Draw Flattened Pixmap require the removal of the padding byte in 32 bit aligned 24 bit image data?
  • Is there a way to scroll through the image if it is larger than the display?
  • Is there a way to hide & redisplay controls (server address, port, run, stop, exit, etc)?
  • Can the Windows banner be removed from the display?
  • Can the Windows keyboard icon be removed from the display?
  • Can you suggest any other optimization?

Thanks for your time,


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Hi Dan,
There is not an alternative to Draw Flattened Pixmap on the PDA.  The only VIs available are those on the Functions Palette.  I am not sure why it requires the removal of the padding byte in 32 bit aligned 24 bit image data, that is something that I would need to ask a developer. 
To scroll through your image, you would need to use the Horizontal Scrollbar Visible or Vertical Scrollbar Visible property nodes.  These property nodes are unsupported by PDA.  To see a list of what property nodes are supported, please see this help file.  I would also suggest going to our Product Suggestion Center and creating a suggestion.
To hide and redisplay controls, you can use a property node for the control and turn the visibility on and off.  When you create a property node for a control, select "visible".  You can then set this to either true or false.
Finally, the Windows keyboard and the Windows banner cannot be removed from display.  I hope that I was able to answer your questions, please be aware that there are many limitations with the Windows Mobile operating system.  Let me know if there is anything else I can do to help, thanks Dan.
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Thanks for the response, Meghan.

I modified the DLL file to output only the 3 bytes of RGB data, and removed the array decimation / interleave.  This cut the display time by 65%, displaying 5 frames per second (almost acceptable, and may be the best that can be done).  I presume the high cost of decimate / interleave is due to memory allocation and copies.

Draw Flattened Pixmap on the PC can accept the 32 bit representation w/o a problem.

I will create a suggestion for scrollbars on PDA images.  The off-screen portions of the image should be available, as Draw Flattened Pixmap and "picture" take proportionally increasing time to process with larger images.

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