UltraChrome Best Practices

High-quality chroma keying with a natural look is fully-achievable with the UltraChrome 2 keying system. However, as with any chroma key system, careful attention should be paid to the chroma key environment.

Keep the following in mind when working with a chroma key:

  • The set should be evenly-lit, with a reasonable level of brightness, too bright or too dark will compromise the ability to produce a great result. High brightness generates high levels of reflected color background (Spill) into the foreground subject. When the camera output is viewed on a waveform monitor, the background set level should read between 50-75% of the overall image level. The foreground subject(s) should be separately lit.
  • Adjust camera shading using appropriate charts, ensuring that grey scale, lens flare, gamma, and white/black balance correctly set. If using the AC-H200-UCHR camera, it is recommended it be set in HDR mode - HLG1200. This mode is compatible with standard (non-HDR) signals and the wider dynamic range allows greater image separation in lower-light regions. Also, the camera should be set at its minimum gain to ensure the lowest noise levels, and detail levels should be kept at minimum to avoid sharp edge transitions.
  • Real elements, presenters, and props should not contain colors similar to the background. Clothing or props with high reflectivity should also be avoided to minimize color spill (colored light reflected from set onto foreground subject).

Masking

The switcher has a mask available for every key channel (including chroma keys), plus an additional mask available to each chroma key channel. Chroma keys can use static box masks or dynamic masks from an external source. Dynamic masks are fed from virtual set systems (such as Ross Voyager) and follow camera moves through camera-tracking data provided by robotic systems.

From the Mask Setupmenu, press Utility Bus Mask and select the input source that has the mask you want to apply.

The Four Chroma Key Commandments

  1. A Great Chroma Key is Made from a Great Original Source — Before attempting to set up the chroma keyer, make sure lighting, background, and talent all look great on the camera; and that camera Gain and Detail have been reduced to a necessary minimum.
  2. No Chroma Key is Ever the Same, Start Fresh with Init — Every set has its own lighting conditions, camera and lens setups, CK wall-quality, consistency of paint, foreground talent clothing, colors, and skin tones. The UltraChrome automatic initialization (Init) does not require color pickers or hue controls; once the general color vector has been selected, it will analyze the entire frame and determine the exact chroma vector and angle of the color background to be removed.
  3. Init, Try, Re-Init and Try Again — The fine-tuning required to get a great result is often minimal and frequently hinges on the adjustment of a single parameter. Changing the value of the wrong parameter can make it impossible to then make corrections with other controls. When learning the nuances of this chroma key, re-Init after making a change that does not achieve the desired result and then try another. Also, all chroma key parameters are saved in the memory system, so you can save a setup and then start over if necessary.
  4. No Last Minute Changes — Once the chroma set, lighting, and cameras are tuned for best performance - don’t change anything! On a normal set, it is common to make last minute tweaks and changes to lighting, iris settings, and even talent/wardrobe. When chroma keying, these changes will require the key to be reset and adjusted - which is fine if you have the time. Avoid change if you can, especially at the last minute, it can substantially lower operator blood pressure.