Double layered optical low pass filter permitting improved image resolution
First Claim
1. An optical low pass filter for use in a color video system for monitoring an object scene having a color encoding striped filter for spatially modulating at least two selected primary color signals while passing a third luminance signal at a higher spatial frequency comprising:
- a first phase retarding filter layer; and
a second phase retarding filter layer, and respective filter layers including a plurality of phase retarding grating stripes, the respective first and second stripes having a nonparallel alignment relative to each other and providing a combined optical transfer function value characteristic of preventing the transmittance of the high spatial frequency signal components of the two selected primary colors while transmitting luminance signals at spatial frequencies above the cut off frequencies of the primary colors, the nonparallel grating stripes preventing spurious primary color signals not representative of the object scene while higher spatial frequency luminance signals are transmitted to provide an improved image resolution.
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Abstract
A double layered optical low pass filter is provided for use in a color video system for monitoring an object scene. The optical filter is designed to optically complement a dichroic stripe filter to prevent the introduction of spurious signals by any interference between luminance and chrominance signals, while at the same time providing a transmittance of high spatial frequency luminance signal to permit an improved image resolution. The optical low pass filter includes a first phase retarding filter layer designed to provide a first spatial frequency response across the visual spectrum and a second phase retarding filter layer designed to provide a second spatial frequency response across the visual spectrum. The combined resultant optical transfer function of the filter layers disclose a cut off of the higher spatial signal components of the primary color design wavelengths of the respective first and second filter layers, while transmitting a higher spatial frequency for the luminance signal to provide the improved image resolution. The specific cut off spatial frequencies of the primary colors and the bandwidth of the luminance signals can be subjectively optimized for any applicable system.
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Citations
10 Claims
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1. An optical low pass filter for use in a color video system for monitoring an object scene having a color encoding striped filter for spatially modulating at least two selected primary color signals while passing a third luminance signal at a higher spatial frequency comprising:
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a first phase retarding filter layer; and a second phase retarding filter layer, and respective filter layers including a plurality of phase retarding grating stripes, the respective first and second stripes having a nonparallel alignment relative to each other and providing a combined optical transfer function value characteristic of preventing the transmittance of the high spatial frequency signal components of the two selected primary colors while transmitting luminance signals at spatial frequencies above the cut off frequencies of the primary colors, the nonparallel grating stripes preventing spurious primary color signals not representative of the object scene while higher spatial frequency luminance signals are transmitted to provide an improved image resolution. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An optical low pass filter for use in a color video system for monitoring an object scene having a color encoding filter means for spatially modulating at least two selected primary colors while passing luminance signals representative of relative light intensity comprising;
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a first phase retarding grating; and a second phase retarding grating, the respective gratings having a nonparallel alignment relative to each other, the design parameters of each grating relating to a respective primary color and providing a combined optical transfer function characteristic of cutting off the higher spatial frequency signal components of the primary colors while transmitting luminance signals having spatial frequency components above the cut off frequency of the primary colors, the respective first and second filter layers satisfy the following equation;
##EQU9##wherein for both layers respectively, χ
is the grating width, a is the lamina width and δ
is the phase retardation, the lamina width for at least one grating being random across the grid. - View Dependent Claims (10)
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Specification