Color correction circuitry and methods for dual-band imaging systems
An imaging system may include a dual-band image sensor that captures visible and near-infrared light and image processing circuitry that performs color corrections on images captured by the dual-band image sensor. The image processing circuitry may analyze each captured image in two different color spaces to determine what type of light source lit each image. The image processing circuitry may determine whether an image was lit by a light source having a relatively high proportion of near-infrared emissions such as an incandescent light, a light source having a relatively low proportion of near-infrared emissions such as a fluorescent light, or a light source having an intermediate proportion of near-infrared emissions such as sunlight or other blackbody radiator. After determining what type of light source lit an image, the image processing circuitry may adjust color balances in that image using a color correction matrix associated with that type of light source.
1. A method of capturing an image comprising:
with a plurality of light-sensitive pixels and a plurality of IR filters in an imager, simultaneously generating image signals from light in a first wavelength band that is associated with near-infrared light and a second wavelength band from light that is associated with visible light; and
with color correction circuitry, generating a color corrected image from the image signals, wherein generating the image signals from light in the first wavelength band that is associated with near-infrared light and from light that is associated with visible light with the plurality of light-sensitive pixels in the imager comprises:
with a first plurality of light-sensitive pixels in the image sensor, generating first image signals from light in the first wavelength band and from light in a second wavelength band that is associated with visible light;
with a second plurality of light-sensitive pixels in the image sensor, generating second image signals from light in the first wavelength band and from light in a third wavelength band that is associated with visible light; and
with a third plurality of light-sensitive pixels in the image sensor, generating third image signals from light in the first wavelength band and from light in a fourth wavelength band that is associated with visible light, wherein generating the color corrected image from the image signals with the color correction circuitry comprises:
comparing the first image signals to the second image signals;
comparing the third image signals to either the first image signals or the second image signals; and
selecting one of a plurality of color correction matrices based on the comparison between the first image signals and the second image signals and based on the comparison between the third image signals and either the first image signals or the second image signals, wherein each of the color correction matrices defines a unique set of first, second, and third weighting factors.
2. The method defined in claim 1 wherein generating the color corrected image from the image signals with the color correction circuitry comprises determining that the image was lit by an incandescent lamp based on the comparison between the first image signals and the second image signals and based on the comparison between the third image signals and either the first image signals or the second image signals and wherein the selected color correction matrix is an incandescent color correction matrix.
3. The method defined in claim 1 wherein generating the color corrected image from the image signals with the color correction circuitry comprises determining that the image was lit by an fluorescent lamp based on the comparison between the first image signals and the second image signals and based on the comparison between the third image signals and either the first image signals or the second image signals and wherein the selected color correction matrix is a fluorescent color correction matrix.
4. The method defined in claim 2 wherein generating the color corrected image from the image signals with the color correction circuitry comprises determining that image was lit by one of a plurality of pre-defined light sources based on a set of comparisons between image signals.