Optimal raw RGB determination for color calibration
AssigneeSony Corporation
InventorsXiaoling Wang, Farhan Baqai, Takami Mizukura, Naoya Kato
Life of this patent
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Abstract
Improving color calibration, and similar operations, by generating an optimal raw RGB color chart, in the raw RGB domain, for an imaging device with a given type of image sensor, such as for a digital still camera. Calibration is performed in response to a constraint which takes into account the spectral sensitivity of the image sensor used on the camera as well as spectral reflectance and spectral radiance of multiple illuminants. Calibration is performed using the raw RGB color chart which is illuminant independent and image sensor specific and which can match the calibration performance of known calibration standards, such as Macbeth 24.
Claims20
An apparatus for generating an optimal raw RGB illumination independent color chart for use with an image sensor, comprising:
- a computer configured for performing image processing;
- and
- programming executable on said computer for performing steps comprising:
- representing spectral sensitivity for a specific type of image sensor;
- deriving a constraint to match calibration performance between a desired optimal raw RGB color chart and a desired color standard under multiple illuminants for a specific type of image sensor;
- applying orthogonal non-negative matrix factorization (ONMF) with the constraint;
- and
- generating an optimal raw RGB color chart for use when collecting an optimal raw RGB data set when performing illuminant independent, image sensor specific color calibration operations.
An apparatus for performing color calibration of a specific type of image sensor within a camera device, comprising:
- a computer configured for performing image processing;
- and
- programming executable on said computer for performing steps comprising:
- generating an optimal raw RGB color chart in response to representing spectral sensitivity for a specific type of image sensor with a constraint derived to match calibration performance with a desired color standard under multiple illuminants, and applying orthogonal non-negative matrix factorization (ONMF) with the constraint,
- performing a white balance under a plurality of different illuminants and initializing an adjustment matrix, determining a first response in an XYZ color space and transforming it to a first response in an L*a*b* color space,
- determining a second response in an XYZ color space under a plurality of different illuminants and transforming it to a second response in the L*a*b* color space, and
- modifying said adjustment matrix to minimize error between said first response in the L*a*b* color space and said second response in the L*a*b* color space.
A method of generating an optimal raw RGB color chart for use in color calibration using a specific type of image sensor for a camera device being calibrated, comprising:
- representing spectral sensitivity for a specific type of image sensor;
- deriving a constraint to match calibration performance between a desired optimal raw RGB chart and a standard under multiple illuminants for the specific type of image sensor for the camera device;
- applying orthogonal non-negative matrix factorization (ONMF) with the constraint;
- and
- generating an optimal raw RGB color chart for use in performing illuminant independent, image sensor specific, color calibration.
Dependencies are inferred from the claim text.