Published on Monday, 01 June 2015

Achtel TrueBlue Filter Records Truer Blues for RED Dragon & RED Epic

The new Achtel TrueBlue optical filter significantly improves the separation of blue colours from unintended red contamination appearing in images shot on the RED digital cinema cameras. The filter was developed by Pawel Achtel MSc, an ACS award winning cinematographer, to reduce the magenta tones in blue colours recorded through the RED cameras’s sensors.

Achtel-RED Dragon NATIVE Achtel-RED Dragon WITH TRUEBLUE
Left: Native quantum efficiency graph for the RED Dragon sensor. Right: The Dragon's quantum efficiency graph with the TrueBlue filter applied.

Distinct from the IR contamination that the sensors may also reveal due to response to IR wavelengths above 700 nm range, these colour phenomena are within the visible spectrum, in particular the blue range from 400 nm to 500 nm wavelength. RED MX and Dragon sensors suffer from notable ‘colour blindness’ in this range, recording magenta-grey instead of reproducing blue.
Achtel-TrueBlue Spectral Response

In an unmodified camera, the problem is visible in bluescreen footage, skies, under water and anywhere where cool colours need to be preserved. The reason is that the red photo-sites on the camera sensor are also sensitive to blue light, as can been seen in the quantum efficiency graphs shown here, measured under controlled conditions at the Achtel laboratory. This contamination gives rise to blues and cool colours affected by magenta, which cannot be removed in post-processing or through colour grading. By fitting Achtel’s TrueBlue filter to the RED camera itself, the problem can be avoided.

Achtel-TrueBlue filter

The TrueBlue filter is supplied as a kit including an optical low pass filter caddy, and is available for RED Epic and RED Dragon digital cinema cameras. It can be installed and removed, as required.

Achtel’s partner Mojo Media Solutions will be showing TrueBlue during the SMPTE15 exhibition to be held in Sydney from 14 to 17 July, including sample footage shot with and without the TrueBlue filter.