Marc L. Simpson

Imaging colorimetry: a new approach.

A new technique is described for the in-process measuring of the color content of images with pixel resolution, using commercially available devices. Color measurement is extremely important in the printing industry for assessing the quality of printed graphic images. Commercially available instruments designed to measure color, in process, have outputs that represent the average color content over specific areas of the printed surface. The color content of an image feature on the printed surface that may be important to consumers is then difficult to assess from these general readings. Instead of an average reading, the technique that we describe provides a color measurement of each pixel within the area of interest on the printing surface so that the color content of specific features can be evaluated.

Intensity-modulated, stepped frequency cw lidar for distributed aerosol and hard target measurements

A compact frequency-modulated, continuous wave (FM-cw) lidar system for measurement of distributed aerosol plumes and hard targets is presented. The system is based on intensity modulation of a laser diode and quadrature detection of the return signals. The advantages of using laser diode amplitude modulation and quadrature detection is a large reduction in the hardware required for processing and storing return signals as well as the availability of off-the-shelf integrated electronic components from the wireless and telecommunication communities. Equations to invert the quadrature signal components and determine spatial distributions of multiple targets are derived. Spatial scattering intensities are used to extract aerosol backscatter coefficients, which can then be directly compared to microphysics aerosol models for environmental measurements. Finally, results from laboratory measurements with a monostatic FM-cw lidar system with both hard targets and aerosols are discussed.

Imaging tristimulus colorimeter for the evaluation of color in printed textiles

The high-speed production of textiles with complicated printed patterns presents a difficult problem for a colorimetric measurement system. Accurate assessment of product quality requires a repeatable measurement using a standard color space, such as CIELAB, and the use of a perceptually based color difference formula, e.g. (Delta) ECMC color difference formula. Image based color sensors used for on-line measurement are not colorimetric by nature and require a non-linear transformation of the component colors based on the spectral properties of the incident illumination, imaging sensor, and the actual textile color. This research and development effort describes a benchtop, proof-of-principle system that implements a projection onto convex sets (POCS) algorithm for mapping component color measurements to standard tristimulus values and incorporates structural and color based segmentation for improved precision and accuracy. The POCS algorithm consists of determining the closed convex sets that describe the constraints on the reconstruction of the true tristimulus values based on the measured imperfect values. We show that using a simulated D65 standard illuminant, commercial filters and a CCD camera, accurate (under perceptibility limits) per-region based (Delta) ECMC values can be measured on real textile samples.

Moment invariants for automated inspection of printed material

The use of moment invariants for the detection of flaws in automated image processing inspection of printed graphic material is investigated. Prior work with moment invariants has concentrated on twodimensional image pattern recognition. A major limitation in pattern recognition applications has been the segmentation of the image from its background. Automated image processing inspection of printed material does not suffer from this limitation because a standard image background exists. The potential for separating flawed and unflawed printed material using moment invariants is demonstrated with formal statistical experiments.

Coherent imaging with two-dimensional focal-plane arrays: design and applications.

Scanned, single-channel optical heterodyne detection has been used in a variety of lidar applications from ranging and velocity measurements to differential absorption spectroscopy. We describe the design of a coherent camera system that is based on a two-dimensional staring array of heterodyne receivers for coherent imaging applications. Experimental results with a single HgCdTe detector translated in the image plane to form a synthetic two-dimensional array demonstrate the ability to obtain passive heterodyne images of chemical vapor plumes that are invisible to normal video infrared cameras. We describe active heterodyne imaging experiments with use of focal-plane arrays that yield hard-body Doppler lidar images and also demonstrate spatial averaging to reduce speckle effects in static coherent images.

All-weather long-wavelength infrared free-space optical communications

ORNL is developing a high-speed, full-duplex all weather communications link for ranges up to 5 kilometers. To accomplish this project, we have constructed an RF-driven waveguide CO2 laser and a dielectric-waveguide Stark modulator. The 10-micron wavelength was selected for its ability to penetrate smoke, fog, and rain. The modulator is based on the Stark shift of NH2D (deuterated ammonia). The laser is driven by a 60 MHz RF amplifier at a power level of approximately 50 watts. The resonator cavity of the laser is formed by a 2.4 mm internal diameter ceramic waveguide with external optics. The RF electrodes are formed from aluminum heatsink extrusions that also provide cooling for the discharge. Details of the laser design will be presented.

Accommodating multiple illumination sources in an imaging colorimetry environment

Researchers at the Oak Ridge National Laboratory have been developing a method for measuring color quality in textile products using a tri-stimulus color camera system. Initial results of the Imaging Tristimulus Colorimeter (ITC) were reported during 1999. These results showed that the projection onto convex sets (POCS) approach to color estimation could be applied to complex printed patterns on textile products with high accuracy and repeatability. Image-based color sensors used for on-line measurement are not colorimetric by nature and require a non-linear transformation of the component colors based on the spectral properties of the incident illumination, imaging sensor, and the actual textile color. Our earlier work reports these results for a broad-band, smoothly varying D65 standard illuminant. To move the measurement to the on-line environment with continuously manufactured textile webs, the illumination source becomes problematic. The spectral content of these light sources varies substantially from the D65 standard illuminant and can greatly impact the measurement performance of the POCS system. Although absolute color measurements are difficult to make under different illumination, referential measurements to monitor color drift provide a useful indication of product quality. Modifications to the ITC system have been implemented to enable the study of different light sources. These results and the subsequent analysis of relative color measurements will be reported for textile products.

Coherent infrared imaging camera (CIRIC)

New developments in 2-D, wide-bandwidth HgCdTe (MCT) and GaAs quantum-well infrared photodetectors (QWIP) coupled with monolithic microwave integrated circuit (MMIC) technology are now making focal plane array coherent infrared (IR) cameras viable. Unlike conventional IR cameras which provide only thermal data about a scene or target, a coherent camera based on optical heterodyne interferometry will also provide spectral and range information. Each pixel of the camera, consisting of a single photo-sensitive heterodyne mixer followed by an intermediate frequency amplifier and illuminated by a separate local oscillator beam, constitutes a complete optical heterodyne receiver. Applications of coherent IR cameras are numerous and include target surveillance, range detection, chemical plume evolution, monitoring stack plume emissions, and wind shear detection.

Color measurements using a colorimeter and a CCD camera

Two new techniques are introduced for measuring the color content of printed graphic images with applications to web inspection such as color flaws and measurement of color quality. The techniques involve the development of algorithms for combining the information obtained from commercially available CCD color cameras and colorimeters to produce a colorimeter system with pixel resolution. 9 refs.

VLSI implementation of moment invariants for automated inspection

The design of a VLSI ASIC (application-specific integrated circuit) for use in automated inspection is described. The inspection scheme uses M.K. Hus (1962) and S. Maitras (1979) algorithms for moment invariants. A prototype design that resolved the long delay time of the multiplier by custom designing adder cells based on the Manchester carry chain was generated. The prototype ASIC is currently being fabricated in 2.0- mu m CMOS technology and has been simulated at 20 MHz. The final ASICs will be used in parallel at the board level to achieve the 230 MOPS necessary to perform moment-invariant algorithms in real time on 512*512 pixel images with 256 gray scales.<<ETX>>