Detectors of infrared focal plane arrays are, in the nature of their photoresponse, nonuniform. Response curves are nonlinear. In view of this, a novel nonuniformity correction algorithm based on the S-curve nonlinear response model and its simplified correction algorithm is proposed. The algorithm is an essential calibration and interpolation correction based on an analytical formula. It requires calibrating in advance, but possesses higher correction precision and wider applicative response range, which is particularly applicable to uncooled infrared focal plane arrays. Borrowing ideas from look-up tables, a real-time hardware correction system, which provides an experimental platform for contrasting different algorithms, is expounded. Experimental results validate that the proposed S-curve model-based algorithm does much better than the two-point correction algorithm and the simplified S-curve model-based correction algorithm.
Proc. SPIE. 7156, 2008 International Conference on Optical Instruments and Technology: Optical Systems and Optoelectronic Instruments
KEYWORDS: Signal to noise ratio, Monochromatic aberrations, Optical transfer functions, Spatial frequencies, Image processing, Wavefronts, Computer simulations, Optoelectronics, Modulation transfer functions, Phase transfer function
The phase mask plays a key role in wavefront coding systems. In order to find the phase coding device with better
performance, a new kind of phase mask - five times phase mask is proposed, based on cubic phase mask in common use,
and its coding properties are studied in the paper. First of all, the reason of depressing spherical aberration is analyzed by
deriving the asymptotic solution to OTF of the wavefront coding systems with five times phase mask. And then we
compare the effects of inhibition of spherical aberration when place the cubic and five times phase mask respectively.
Finally, the experimental simulation is done. The results show that on the specific threshold (MTF=0.1) the normalized
bandwidth of the system with five times phase mask can be reached 3 times of that with the cubic one; at the same
characteristic frequency (u = 0.5), the MTF value is 2 times of that in system with cubic one. Both the MTF consistency
in the low frequency region and the PTF consistency in the high frequency region of the system with a five times phase
mask are better than those with a cubic one in condition of different spherical aberration. Compared with the cubic phase
mask, the five times phase mask performs better in inhibition of spherical aberration.
High-power LEDs of different color have generated much enthusiasm because of the potential energy savings and
reduced maintenance cost due to long lifetimes compared with traditional light source. Two schemes are widely used for
LED dimming: continuous current dimming, or pulse-width modulation (PWM) dimming. The visual felling to the LEDs
is the most intuitive judgment in the LED illumination and display. But the apparent brightness of the LEDs under these
dimming ways has never been studied. In this paper, the research of the apparent brightness is approached through
experiments. The results show that when the average intensities are the same, the apparent brightness of the PWM
dimming LED is higher than that of the continuous dimming LED. In addition, to the PWM dimming LEDs, the contrast
apparent brightness of various color LEDs is obviously discrepant as the duty cycle is less than 40%, but when it is
above 40%, the gap between the contrast values becomes much smaller. Thus, in the LED applications, the LEDs using
PWM driving method has higher brightness efficacy, and the duty cycle of the PWM should be above 40% to achieve the
consistent apparent brightness between LEDs. The results have great availability to optimize the driver for the LEDs.
This paper deals with the problem that a great number of rotary joints are suffering the conflict between high efficiency of signal dynamic coupling and low requirement of precision mechanism. As a solution, a specific design of the infrared spatial interconnection rotary joint is presented accompanying with the discussion of requirements for the mechanism and the circuit. Benefit from infrared data interconnection between the stator and the rotor, the security of data transfer is ensured and the off-axis angle can vary from 0º to 30º, which contribute to a simpler mechanism and a compact rotary joint. Relative experiment shows that with this rotary joint, signals can be transmit securely, and the efficient data transmission speed is up to 1.4Mbps under Windows 2000 circumstance.