DLP4500: Hi, I think I have scanning lines interfering with my patterns and I don't know how to get rid of them.

Hello Emilie,

To clarify do you only see these artifacts if you have too short of a pattern period? If you look at table 8 in the DLPC350 datasheet you can see the fastest supported frame rates.

Could you also please confirm the version of the SDK and version of the DLPC350 firmware you are using?

Thanks,
Kyle

Hello,

Thank you very much for the fast reply.

Sorry for the confusion, the artefacts happen whatever the frequency of the sine patterns (this does not seem to be linked from what I have observed) and seem to only depend on the pattern exposure time (when I said high frequency I meant low pattern exposure time). The width of the lines seem to increase when pattern exposure increase also.

According to table 8 of DLPC350 datasheet I should be capable of reaching 120Hz (around 83'000 us pattern exposure) which seem way below my 'cutting' frequency of 1.8Hz (corresponding to the 540'000us pattern exposure time I have to use to get proper snapshots) I would like to at least be able to reach 60Hz ideally...

I am using DLPR350PROM_v4.0 version of firmware and I don't use SDK I do everything via the GUI only.

Thank you in advance for your support, Emilie

Hello Emilie,

These lines appear to coming from the camera capture side. What kind of camera are you using, the bars appearing seems to coming from rolling shutter camera, and also by the way is the camera hardware triggered? Either way - camera triggering projector or projector triggering camera. 

Please verify if the camera is able to synchronize and capture for bigger exposure times. 

If you still see issue, could you also do one more experiment, rotate the projector by 90-degree and run the same experiment, now see if the bars appear differently...

Regards,

Sanjeev

Hello,

I am using Fastcam MC2.1 (10K) from Photron that records from 50fps to 10'000fps, global shutter.

The artefacts can be seen naked eyes and the picture previously uploaded is from my phone ( iPhone 7) but they also are visible on the recordings of the synchronized camera.

I am using an external pulse (4.5V) as external trigger (Trigger IN) that is simultaneously transmitted to the light and to the camera (BNC) and it correctly synchronizes according to my tests.

Rotating the projector did not change anything.

Could you please tell me where I can find the projector scanning speed ? Thank you.

Thank you very much for your help, Emilie

Hi Emilie,

For projector speed, depending on the pattern sequence mode - Pattern Sequence or Pattern Sequence [ variable exposure]

You can look at these parameters, the projector speed will be accordingly.

Regarding your trigger setup, I recommend trigger between camera and projector not independently via another common source.

You can do the following two arrangements 

1. External Pulse -> (trigger in) LightCrafter 4500 (trigger out) -> (trigger input) Camera

2. External Pulse -> (trigger in) Camera (trigger out) -> (trigger input) Projector

Also you mentioned the camera can do 50fps to 10000fps, for example when you set projector exposure at ~0.5 seconds, are you also setting the camera exposure time to (~0.5 seconds ) at min 50fps (the camera integrate only 20ms worth data). So may be we are missing something here??

I think camera exposure setting is not matching to the projector exposure and you end-up reading partial data only due to the smaller exposure time.

By the way does 8.3ms exposure works with the camera? In the camera in external trigger mode, the exposure time can be set to around the projector exposure time...

Hope this helps.

Regards,

Sanjeev 

Regards,

Sanjeev

Dear Sanjeev,

I have the same settings as you in the gui...

So here is samples of what I get using minimum rate i can have: 50fps. I do not try to image at 2Hz I obviously cannot and this is why I want to be able to reach at least 50fps... But at least from the eye and phone camera point of view,it seems that around this frequency the lines are not visible anymore. So the 50fps synchronized camera also sees the some wierd lines...And Interestingly when I only use 2 patterns alternatively (but I need to use more) the lines do not appear and I can verfy that my synchronization works correctly. ( but as proposed I am  also working on finding a way to connect them directly for the triggering but according to the pictures the synchronization seem to work)

Here are camera view examples taken with the exact same settings: 

When using only 1 pattern (50fps / 20ms) everything works fine....

When using 2 patterns (50fps / 20ms) everything works fine also...

But then when i try to add one more patterns, then more than 2 patterns, the strange lines appear. And it is not even a periodic phenomenon.

Thank you very much for your time, Emilie