Characterizing reflectance, illuminance, and sensor response for electromagnetic radiation
Introduced here are computer programs and associated computer-implemented techniques for determining reflectance of an image on a per-pixel basis. More specifically, a characterization module can initially acquire a first data set generated by a multi-channel light source and a second data set generated by a multi-channel image sensor. The first data set may specify the illuminance of each channel of the multi-channel light source (which may be able to produce visible light and/or non-visible light), while the second data set may specify the response of each sensor channel of the multi-channel image sensor (which is configured to capture an image in conjunction with the light). Thus, the characterization module may determine reflectance based on illuminance and sensor response. The characterization module may also be configured to determine illuminance based on reflectance and sensor response, or determine sensor response based on illuminance and reflectance.
1. A method comprising:
defining a series of overlapping spectral wavelets spanning a region of the electromagnetic spectrum;
producing a weight for each spectral wavelet by establishing how the series of overlapping spectral wavelets best fit a specified reflectance spectrum; and
generating a universal fingerprint by applying the series of weights to a series of reflectance spectrums.
2. The method of claim 1 , wherein the region of the electromagnetic spectrum corresponds to a bandwidth of a multi-channel image sensor.
3. The method of claim 1 , wherein the series of reflectance spectrums are uniformly spaced across a target region of a color space.
4. The method of claim 3 , wherein the target region of the color space corresponds to human skin tones.
5. The method of claim 1 , wherein the series of reflectance spectrums correspond to at least some of color evaluation samples in Illuminating Engineering Society (IES) Technical Memorandum (TM) 30-15.
6. The method of claim 1 , further comprising:
generating a hardware-related fingerprint for the series of reflectance spectrums; and
solving a transformation matrix that specifies what transformations, if any, are needed to transform the hardware-related fingerprint into the universal fingerprint.