Spectral synthesis for image capture device processing
A substantially rectangular spectral representation is synthesized, which is adapted to produce image capture device sensor outputs if applied to an image capture device. The synthesized substantially rectangular spectral representation can be utilized in generating output color values of an output color space from image capture device sensor outputs, where the image capture device sensor outputs correspond to an image captured by an image capture device. The generated output color values correspond to colors perceived by the human visual system for the same image as that captured by the image capture device. Image capture device gamut is also determined.
1. A spectral synthesis module to generate color output signals in response to image capture device sensor outputs, the spectral synthesis module comprising:
a linearization module to receive first, second, and third camera-processed device sensor outputs and generate first, second, and third linearized camera color values;
a camera-color temperature module to receive the first, second, and third linearized camera color values and generate estimated first, second, and third raw color values;
a processing module to divide the estimated second and third raw color values by a first scale factor (Σ) to generate first and second scaled color values (p,q), wherein the first scale factor is generated by adding together the estimated first, second, and third raw color values;
a wavelength determination module to determine a first transition wavelength λ ↑ and a second transition wavelength λ ↓ a rectangular spectra representation, wherein the first transition wavelength corresponds to a transition from zero to a first value and the second transition wavelengths corresponds to a transition from the first value to zero;
a mapping module to map the first and second scaled color values based on the first and second transition wavelengths, a transition scaling factor that extends the rectangular spectra representation for a general spectral representation of light, and a parameter that represents a low value for the rectangular spectra representation to determine a first set of color output values;
a multiplier module to multiply the first set of color output signals with the first scale factor to output a second set of color output values; and
an output module to output color output signals based on the color output values.
2. The spectral synthesis module of claim 1 , wherein the linearization module comprises one or more 1-D LUTs.
3. The spectral synthesis module of claim 2 , wherein the one or more of the 1-D LUTs comprises a function to map input values to inverse logarithmic output values.
4. The spectral synthesis module of claim 1 , wherein the camera-color temperature module comprises applying a 3 × 3 camera color-dependent matrix to the first, second, and third linearized camera color values to generate the estimated first, second, and third raw color values.
5. The spectral synthesis module of claim 1 , wherein the camera-color temperature module is determined under the constraint that all of the generated estimated first, second, and third raw color values are larger or equal to zero.