Spectral and spatial calibration illuminator and system using the same
A method of spatially and spectrally calibrating a spectrophotometer including: a) emitting a white light illumination output from a full width illumination source; b) illuminating a test patch with the white light illumination output; c) reflecting a portion of the white light illumination output from the test patch to form a white light reflected illumination output; d) receiving the white light reflected illumination output at first, second and third rows of photosensitive elements to form a first calibration data set; e) emitting a cyan light illumination output from the full width illumination source; f) illuminating the test patch with the cyan light illumination output; g) reflecting a portion of the cyan light illumination output from the test patch to form a cyan light reflected illumination output; and, h) receiving the cyan light reflected illumination output at the second and third rows of photosensitive elements to form a second calibration data set.
1. A method of spatially and spectrally calibrating a spectrophotometer comprising a full width illumination source and a full width photodetector array, the full width illumination source comprises a first plurality of spectral outputs and a second plurality of spectral outputs, and the full width photodetector array comprises adjacent first, second and third rows of photosensitive elements, the first row of photosensitive elements comprises a red filter, the second row of photosensitive elements comprises a green filter, and the third row of photosensitive elements comprises a blue filter, wherein the first plurality of spectral outputs combine to form a white light illumination output and the second plurality of spectral outputs combine to form a cyan light illumination output, the method comprising:
a) emitting the white light illumination output from the full width illumination source;
b) illuminating a test patch with the white light illumination output;
c) reflecting a portion of the white light illumination output from the test patch to form a white light reflected illumination output;
d) receiving the white light reflected illumination output at the first, second and third rows of photosensitive elements to form a first calibration data set;
e) emitting the cyan light illumination output from the full width illumination source;
f) illuminating the test patch with the cyan light illumination output;
g) reflecting a portion of the cyan light illumination output from the test patch to form a cyan light reflected illumination output; and
h) forming a second calibration data set from the cyan light reflected illumination output received at only the second and third rows of photosensitive elements.
2. The method of spatially and spectrally calibrating a spectrophotometer of claim 1 further comprising:
i) determining a calibration matrix based on the first and second calibration data sets.
3. The method of spatially and spectrally calibrating a spectrophotometer of claim 1 wherein the full width illumination source comprises:
a light pipe comprising first and second ends;
a first light emitting diode adapted to emit the white light illumination output; and,
a second light emitting diode adapted to emit the cyan light illumination output,
wherein each of the first and second light emitting diodes is optically coupled to the first end or the second end.
4. The method of spatially and spectrally calibrating a spectrophotometer of claim 3 wherein at least one of the first and second light emitting diodes is optically coupled to the light pipe by a fiber optic element arranged therebetween.
5. The method of spatially and spectrally calibrating a spectrophotometer of claim 3 wherein the light pipe is arranged to produce the white light illumination output and the cyan light illumination output substantially uniformly along the light pipe.
6. The method of spatially and spectrally calibrating a spectrophotometer of claim 1 wherein the full width illumination source is arranged to produce the white light illumination output and the cyan light illumination output substantially uniformly along the light pipe.
7. The method of spatially and spectrally calibrating a spectrophotometer of claim 1 wherein the full width illumination source comprises a first row of light emitting diodes adapted to emit at least one of the white light illumination output and the cyan light illumination output.
8. The method of spatially and spectrally calibrating a spectrophotometer of claim 7 wherein the full width illumination source further comprises a second row of light emitting diodes adapted to emit at least one of the white light illumination output and the cyan light illumination output.
9. The method of spatially and spectrally calibrating a spectrophotometer of claim 1 wherein the test patch comprises a full width image having a uniform color in a cross process direction.
10. The method of spatially and spectrally calibrating a spectrophotometer of claim 1 wherein the test patch comprises a full width image having a non-uniform color in a cross process direction.
11. The method of spatially and spectrally calibrating a spectrophotometer of claim 1 wherein the white light illumination output is formed by a blue light emitting diode in combination with a yellow phosphor layer.
12. The method of spatially and spectrally calibrating a spectrophotometer of claim 11 wherein the blue light emitting diode is an indium gallium nitride (InGaN) light emitting diode.