3, 4 Since digital camera sensors do not naturally adapt in this manner, incorrect white balance (WB) will arise when the WP of the scene illumination differs from the reference white of the output-referred color space used to encode the output image produced by the camera. Although the various adaptation mechanisms employed by the HVS are complex and not fully understood, it is thought that the HVS naturally uses a chromatic adaptation mechanism to adjust its perception of the scene illumination WP to achieve color constancy under varying lighting conditions. The second issue that must be addressed is the perception of the scene illumination WP. 2.4, along with an illustration of how T _ should be normalized in practice. The characterization methodology for determining the optimum T _ is described in Sec.
Significantly, this means that the optimum T _ depends upon the nature of the scene illuminant, 1, 2 including its white point (WP). The relationship can be optimized for a given illuminant by minimizing the color error. In general, camera raw spaces are not colorimetric, so the above conversion is approximate. The connections with the color conversion methods of the DCRaw open-source raw converter and the Adobe digital negative converter are also examined, along with the nature of the Adobe color and forward matrices.Įq. Several advantages of the approach used by traditional digital cameras are discussed.
The strategy used by internal image-processing engines of traditional digital cameras is shown to be based upon color rotation matrices accompanied by raw channel multipliers, in contrast to the approach used by smartphones and commercial raw converters, which is typically based upon characterization matrices accompanied by conventional CATs. Various color conversion strategies that are used in practice are subsequently derived and examined. In this article, the nature of a typical camera raw space is investigated, including its gamut and reference white. Color conversion matrices and chromatic adaptation transforms (CATs) are of central importance when converting a scene captured by a digital camera in the camera raw space into a color image suitable for display using an output-referred color space.
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