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Stable image without camera trigger in pattern mode

Lukas Klodt
Prodigy 20 points

Hi,

i am using LighCrafter for an adaptive lighting system and have some problems with image fluctuation.

I want to display a static 8-bit image.

I started with static image mode but then i noticed the S-shaped gamma correction curve,

so now i'm using pattern mode to display a single image with the following parameters:

Bit Depth: 8
Number of Patterns: 1
Include Inverted Patterns: no
Trigger Type: auto

Trigger Delay: 0
Exposure Time: 0 (read out value: 8333)
Trigger Period: 0 (read out value: 8568)

1. Using a camera exposure unequal to the trigger period gives a strong fluctuation in my image brightness (as expected due to the pulse width modulation to display gray value)

2. If i set my camera exposure close to the trigger period value, i get a more or less constant image if i capture it at a random point in time, but i think it's not optimal, because i'm not synchronized with the projector. Even if i use multiples of the trigger period (e.g. ~102 ms) i notice a slow pulsation (with a few seconds cycle time) in brightness if i watch the images as video (10fps). My guess is that it's because of the time between switching of the patterns (even if its only 1 pattern).

So here are my questions: What happens between patterns if i only have 1 pattern? What is the state of the mirrors inbetween?

Do i still have a delay to rotate buffers or anything like that?

And is there any easy way to get a stable image (repeated image captures) without camera trigger?

If there is a way to set exposure time and trigger period to the same value (for 1 pattern), that would probably solve my problem.

(btw. i use the C sample code to communicate with my lightcrafter, firmware version 1.1)

Help is appreciated.

  • 0
    TI__Genius 9935 points

    Lukas,

    Welcome to the DLP & MEMS E2E forum.

    The meaning of "static" is that the image is not changing frame to frame. There really is no such thing as a static image on the DMD. The mirrors are being set and reset for every frame - at whatever rate this is set to happen.

    The LightCrafter values must be set, then you can read them out to make sure that you have properly set them.

    As you state, the variations in the image which you are seeing on your camera are due to the unsynchronized rate between the camera shutter and the LCr display frame rate. That is why the LCr provides both output and input triggers for synchronizing cameras with the LCr. Each multi-bit (8 bit, for example) image actually consists of a number of subframes which occur much faster than the "frame" rate. It is very difficult (impossible) to avoid the "beat" frequency between the camera and the LCr patterns without using the trigger to synchronize the LCr and camera.

  • 0 in reply to Pascal DLP
    Prodigy 20 points

    Thanks for the quick response.

    I guess that means i have to use the trigger signals after all if i want better results or maybe try to use lower bit-count images with even longer exposure times.

  • 0 in reply to Lukas Klodt
    Prodigy 20 points

    Ya, for this image questions, maybe you have to trigger signals with on other choice.