Comparing different ACES Input Device Transforms (IDTs) for the RED Scarlet-X Camera

Abstract

The RED film cameras are important for professional film productions. Therefore, the Academy of Motion Picture Arts and Science (AMPAS) inserted to their new Input Device Transforms (IDTs) in ACES 1.0.3 among others a couple of conversions from RED color spaces. These transforms are intended to establish a linear relationship of the recorded pixel color to the original light of the scene. To achieve this goal the IDTs are applied to the different RED color spaces, which are provided by the camera manufacturer. This results in a linearization of the recorded image colors. Following this concept the conversion should render comparable results for each color space with an acceptable deviation from the original light of the scene. In color science color space conversions need a documentation of the three main components of the individual color spaces: primaries, whitepoint and transfer function. For the RED colorspaces in question these parameters are only available for the REDWideGamutRGB color space, whereas the other color spaces are not documented. For this reason the behavior of the color conversion can only be tested, but not calculated. The goal of this paper is to compare the results of the color conversions of the main RED color spaces: REDWideGamutRGB, REDcolor4 and REDdragoncolor2. Additionally a conversion to the for television usage important color space REC2020 (ITU-R BT.2020) is added. The test setup contains a GretagMacbeth ColorChecker, which is recorded by a RED Scarlet-X camera and a mobile spectrometer (rgbphotonics Qmini). The latter captures the spectral distribution of the individual ColorChecker patches under the same lighting conditions. To compare the results, the recordings of both devices were converted to the CIE xy-chromaticity diagram using The Foundry Nuke11X. Additionally a comparison to reference data provided by the ACES document TB- 2014-004 is included. Finally it is reviewed if the ACES IDT concept is working for the RED Scarlet-X camera.