LED Flicker and Video

One of my activities more common activities during the Christmas season is designing lighting for my church using a variety of fixtures they have acquired overtime. While the majority of their LED product is of good quality they do have some off brand lights that flicker on video. This is a common problem with cheaper LEDs built with lower quality components. So here's and explination of why and a work around for recorded video only.

The video flicker comes from the way that the individual colored diodes are dimmed to color mix or for intensity. In order to dim an LED it is turned on and off rapidly maintaining its nominal operating voltage when in the on state. This helps preserve color integrity and relative brightness throughout the cycle no matter how long the LED is actually on. The process is known as pulse width modulation or PWM. For a look at this see the picture on the right. More often than not, this process happens more rapidly than the eye is able to perceive however sometimes camera's are able to pick this up due to their frame rate and shutter speeds. This process becomes more noticeable as the LED is "dimmed" (turned on less frequently in the waveform) such as when the fixture is at a low level or if certain colors are mixed. While the LED product may work well for live events without video there is no way to fix the problem when using video and the flicker is going to happen any time a camera is used. The best way around this is to buy "camera friendly" products that have a high PWM frequency or rely on other methods of dimming.

After doing some research I was able to find a solution that works decently for RECORDED video. I'm almost positive that this can not be employed on live video. Any ways here are the steps:

Open the video in an editing software that allows you to manipulate tracks (Final Cut, Adobe Primeier, Sony Vegas, etc.)

Copy the video track with the offending LEDs from the main track to a secondary one on top of the main

Delete the audio from the secondary track

Offset the secondary video by a frame or two

Set the opacity of the second track to ~50-60%

After messing around with the opacity and frame offset of the second track you end up with something masking the LED flicker. The video ends up turning out fairly decent but judge for yourself:

Mounting an SD Card as a Standard Hard Drive

In my previous post I mentioned that one of the limitations of the windows tablets I had come across is the small amount of available storage. The simplest way around this is to add an SD card. Unfortunately, windows will not allow you to install programs to an SD card and some programs will not use it as storage. A way around this is to mount the SD card as a virtual hard drive. Here are a list of steps to get this done. This method works with Windows 7 on (upgrading my tablet to Windows 10 broke the logic so I can confirm it for Windows 10):

  • Ensure the card is formated as NTFS (Computer> Right Click on SD Card> Format)
    • You may want to wipe the data even if the card is properly formated
  • Open Disk Management Utility by searching for "diskmgmt" from the search bar
  • In the Disk Management window right click on the left side and select "Change Drive Letters and Path..."
    • Click "Remove"
      • This will cause it to no longer appear in the computer menu
    • Click "Add"
      • Under "Mount in Following Empty NTFS folder" type "C:\Media Container" (Or whatever you'd like just be sure to remember it for later)
    • Click "OK"
  • Return to the main Disk Management Windo
    • Click Actions> Create VHD menu
      • Click browse and specify the location of the SD card (C:\Media Container)
      • Save a the file as "Media Store" (Again can be your choice)
      • Set the size to match the SD card
      • Select the VHDX option
      • Select the Dynamically Expanding option
      • Click "OK"
    • Right click on the left side of the new disk and select "Initialize Disk"
      • Use the GPT option
    • After it completes right click on the right side and select "New Simple Volume"
      • Click through with all defaults
    • Save and exit out

In order to make this a permanent fix there are a few more steps that need to be taken.

  • Create a . txt file in "C:\Media Container"
    • Add the following to the file
select vdisk file = "C:\Media Container\ MediaStore.vhdx"

attach vdisk

assign letter = D
  • Launch the Task Scheduler by searching for it in the start men
    • Click Create Task
    • Name Task "Mount SD" or something along those lines
    • Change the account to "SYSTEM"
    • Goto Triggers Tab
      • Click "New.."
      • Set begin task to "At Startup"
      • Click "OK"
    • Goto Action Tab
      • Click "New"
      • Set Action to "Start Program"
      • Under Program/script add "diskpart"
      • Add arguments "/s "C:\Media Container\Mount Script.txt""
      • Click "OK"
    • Click "OK" and exit out

After rebooting your computer you should see a "D" drive that was formerly an SD card. Now you should be able to use it as a normal hard drive.

The information from this post originally came from the Superuser Forums but has been expanded and simplified to make it easier to follow.

Windows 8 Tablet for Lighting Work

One of the most important tools a lighting programmer can have these days is solid personal computer. As a matter of personal preference, I lean more towards using windows computers over a Mac due to the wider range of software choses and ability to customize. One of the recent trends that caught my eye was the small convertible netbook/ tablet. They tend to be on the inexpensive side and seem like a good field computer that I don't care too much about getting damaged. So I decided to buy an Asus Transformer T100TA that keeps showing up on deal website such as Woot.com for about $200. While it doesn't replace my main laptop it still offers me some additional flexibility in how I can do things. It weighs next to nothing, even with the keyboard attached, and has all day battery life (~ 10hrs) allowing to go anywhere. It has more functionality than my iPad as well and has even come with me to several gigs when I just didn't need my full laptop but actually wanted to get some work done. In fact this post is being written on it!

Here's a quick look at the specs:

  • Full Windows 8.1 upgraded to Windows 10 (fixed with Classic Shell)
  • Intel Atom Z3775 Quad Core @ 1.46ghz
  • 2 Gigs of Ram
  • 64GB internal storage
  • 10.1 Inch Touch Screen (1368x768)
  • MicroSD Slot (Capable of reading 128GB cards, see this post on how to make this more useful)
  • Micro USB 2.0 (Charging and OTG)
  • Micro HDMI
  • USB 3.0 on Keyboard
  • 2.4lbs w/keyboard

Looking at the specs its not an overly powerful machine but it has enough horse power to get things done.  The biggest advantage is the full version of Windows, meaning you can run just about any software on it as long as it doesn't need a ton of processing power/RAM, unlike other tablet options. The hard drive space a somewhat of a limit but there are ways to work around this. In my next post I'll give you the steps I used to get the OS to think an SD is a regular hard drive and install programs such as Drop Box to it allowing you to greatly expand the SD cards utility. When used with USB Ethernet adapter you can join wired networks and use programs like remote desktop to access other network computers or other show critical functions you may not want on WiFi. 

Here's the list of lighting type programs I've tried and some of the results:

  • Magic Q- Works great, outputs fine over the USB dongle, the touch screen is nice too. I actually ended up running a small show off it in a pinch.
  • EOS Offline- Runs as expected, able to connect to a console as a client, haven't tried outputting via Nomad
  • Grandma 2 OnPC- Runs but needs a wired connection via USB> Ethernet
  • Reaper- Works fine for audio, video not so much

All of this comes together to create something that is worth considering if you want a utility computer or are a Mac user looking to get into Windows for certain applications with a very reasonable price tag.