19 January 2009 Automatic white balance: whitebalPR using the dichromatic reflection model
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Abstract
The current color constancy methods are based on an image processing of the sensor's RGB data to estimate the color of illumination. Unlike previous methods, whitebalPR measures the illuminant by separating diffuse and specular components in a scene by taking advantage of the polarizing effect occurring to light reflection. Polarization difference imaging (PDI) detects the polarization degree of the neutrally reflected (specular) parts and eliminates the remitted (diffuse) non-polarized colored parts. Different experiments explore the signal level within the polarization difference image in relation to multicolored objects, different object surfaces and to the arrangement of light source, camera and object. The results exhibit a high accuracy of measuring the color of illumination for glossy and matte surfaces. As these setups work best for achromatic objects, this new approach for data analysis combines the ideas of the dichromatic reflection model (DRM) and whitebalPR and delivers reliable results for mainly colored objects. Unlike the DRM needs to segment the image referring to the objects in the scene, the new proposal (polarization difference line imaging, PDLI) is independent from any knowledge of the image content. A further arbitrarily segmentation of the image into macro-pixels of any size reduces the computational effort and diminishes the impact of noise on the PDI signal. An according experiment visualizes the coherency between the size of the macro-pixels, the angle of incidence and the accuracy of the process. To sum up, by means of the segmentation the PDLI process gains further stabilization in detecting the color of the illuminant while the computational effort decreases.
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Matthias Sajjaa, Matthias Sajjaa, Gregor Fischer, Gregor Fischer, } "Automatic white balance: whitebalPR using the dichromatic reflection model", Proc. SPIE 7250, Digital Photography V, 72500D (19 January 2009); doi: 10.1117/12.805404; https://doi.org/10.1117/12.805404
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