"Scanlines" seen on camera when projecting images via HDMI to DLP9000? Advice on how to fix?

Hi Henry,

Can you provide more details about what exposures you are testing at? It sounds like the Lightcrafter 9000 doesn't have enough time to load an image to the device before the next one comes in.

Any further/specific details you can provide will help us diagnose your issue.

Thanks,
Paul

Hi Paul,

Thanks for getting back to me! 

By 'exposure times,' I'm assuming you're referring to the USB camera I'm using to image the DLP - I first noticed flickering at the camera's 100 millisecond exposure setting, and decreasing the exposure to around 0.1 milliseconds clearly shows the scanlines 'moving' across the surface of the image. 

The thing is, we aren't loading a succession of images: at this stage we are only displaying one image, and the feed we see in the video is supposed to be static image. Technically, nothing about the DMD should be changing since we're only displaying a single image at this point. 

Further details on setup that I think might be salient are (some repeated from my initial post): 

• Windows 10 computer with an HDMI connection directly to the DLP.
• Visual Studio 2012 is the program being used to display images on the DLP. 
• We are uploading a single image (right now a plain circle).
• Using the camera at an exposure setting of ~ 0.100 ms shows scanlines 'traveling' across the image. 
• Please use this link to view a recording of the phenomenon as we see it on our screen: 
  

Henry,

Thanks for the video. A couple more questions:
1. Is the camera global or rolling shutter?
2. What image are you displaying with the projector?
3. What is your projector exposure time?

I suspect that what you are seeing is an artifact from a rolling shutter camera. DLP is a time-multiplexing technology and we rely on the eye to correctly integrate all the bit planes for a proper image. With a rolling shutter camera, you can run into a situation where the camera is catching different bit planes being displayed as the image is captured, causing effects like the one you're seeing.

See if you can put your camera into a global shutter mode. That will solve the problem.

-Paul

And to further elaborate on my global shutter comment, you'll need a way to sync the camera to the beginning of the image frame and set the exposure long enough so that all the bit-planes are captured.

Paul

Hi Paul,

To answer your questions: 

1. Is the camera global or rolling shutter?

I got on the phone with Amscope's tech support; the MU035 is a USB2.0 camera that employs what they call an Electronic Rolling Shutter. It doesn't seem to have an option to switch to a global shutter, unfortunately. 

2. What image are you displaying with the projector?

As can be seen from the video in my previous post, I'm projecting a blank circle. Our working image format is monochrome BMP, so 'active' areas are 'white' and 'inactive' areas are 'black.' When feeding the image to the DLP via the computer, we're giving it a 2560x1600 monochromatic BMP with a white circle in the middle. We're not displaying multiple images either; this blank circle is a single 'frame', so perhaps my knowledge is lacking but I'm not entirely sure that there are 'multiple' bit planes to integrate for the camera. 

3. What is your projector exposure time?

I'm not entirely sure what you mean by 'projector', my apologies. In this case, we're not using the DLP in a projector unit like we'd see in a theater - we have a homebrew setup where as the DLP scrolls through a series of images, we shine line continuously until the image stack is done and then we turn the light off. 

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The odd thing about this whole thing is that when we use the software the DLP came with to load images to it (using Pattern-on-the-Fly Mode), any images we see on the DLP are fine, with none of these scanline artifacts.

However, when we connect to the DLP with our HDMI cable and attempt to use it like a second display, then we get these scrolling scanline artifacts. 

Henry,

Sorry for my imprecise language - when I say projector, I simply mean the DMD chip. Just to confirm - you're using a Lightcrafter 9000, correct?

(3) By exposure time here, I'm interested in what your pattern settings are.

It looks to me like you're seeing some sort of blanking or syncing artifact from the HDMI video input. Let me do a little digging and get back to you on what this might be.

Paul

Hi Henry,

Please do the following:

* Adjust the secondary monitor output settings so that the refresh rate is as low as possible. Does the issue go away?
* In HDMI video mode, reduce the frame rate as low as possible with monitor adjustments.
* In video streaming mode, make sure the source output matches the DMD resolution and display your pattern as a 1-bit pattern to keep the refresh rate low.

The lines you're seeing are from the rolling shutter behavior refreshing on the incoming HDMI video frames.

Let me know if any of the above adjustments help.

Thanks,
Paul