Picture-refreshing frequency issue

Question

Hello,
I got this problem: I display 3 different pictures in a sequence. Whole sequence last 1 second (0,3333 per picture) and is repeated continuously. While doing this, I've got some displaying issues - some white flahes occours on the pictures. This is easily visible, as pictures have black background. Those flashes appear as white stripes or fields oriented horizontally in different part of picture. I think this is some refreshing issue, but I'm not sure about it and don't know how to check it. I did not succeed at making print screen of those flashes, which I think confirm this is some displaying issue. I want to know what You guys think about it, if can it be solved, is this my hardware issue or some kind of LabVIEW limitation. I've checked it on 3 different displays (my laptop screen, my PC LCD screen, projector) with 50-60Hz refresh frequency and results were the same. I've tried with different picture resolutions and I think these flashes are more common in bigger pictures.
I attach all VI I use to display those images and some reference pictures for You to check if You too got this issue.
Few words about how this VIs work:
There are 2 VIs - controling one and displaying one. I need it this way as I want to have pictures displayed on second monitor while being able to adjust them from front panel on 1st monitor. So there is this Displaying VI which only displays images, and Controling VI which sets all parameters. To get it work, You need to open Displaying VI and make it run. Then You open either ControlingPredefine or ControlingGenerated, set:
Interval value (time between changing pictures, 333 is my case),
VI path (this should be path of Displaying VI)
monitor (0 - main screen, 1 - second screen if You have. I made it this way as I've been checking it with different monitor configurations (laptop only vs laptop + projector))
and run it. When set correctly Displaying Vi should be fullscreened on monitor set in monitor control and display 3 pictures in Interval
There are 2 Controling VIs:
Predefined works on existing jpg pictures chosen from hard drive (there are 3 additional path controls which need to be set before running)
Generated generates pictures in the real time, you can chose between 2 figures (circle/square) and set 3 sizes (each for each picture in sequence)
Stop button from Controling Vi stops both VIs (Controling and Displaying).
I attach 2 sets of pictures (small and big) made in paint.
My LabVIEW version is 2011
Solved!
Go to Solution.
Attachments:
VIs.zip ‏64 KB
Pictures.zip ‏22 KB

Answer 1

Chudy,
I looked at the ControlingGenerated VI and do not see the flashes.  I did add the Run VI node and similar changes.  I tried it with your original Displaying VI and with one I modified to include a delay.  When I set both delays to zero or very small values, it appears that the two images can get out of sync.  I suspect that this is due to the screen update rate by the OS and not specifically something in the VI.
It really does not make any sense to update faster than the OS will write to the screens.  The excess data will be ignored.
Similarly, you should separate the communications with the serial port from the screen updates.  Look at the Producer/Consumer Design Patterns which come with LV.  Read the serial port in a parallel loop which is dedicated to just that task. Typically queues are used to pass data from one loop to the other.
Here is a version I modified to use a queue and to call Displaying as a subVI rather than via an Invoke node.  Notice that the Displaying VI no longer uses the Loop Terminator and that the timing is set by the Dequeue wait.  The Displaying loop will run the same number of times and at the same average rate as the main loop.
Lynn
Attachments:
ControlingGeneratedBeta.23.vi ‏20 KB
Displaying.23.vi ‏27 KB