Joni Orava

Color and Image Characterization of a Three CCD Seven Band Spectral Camera

In this study spectral and spatial characterization of a seven channel FluxData 1665 MS7 three-CCD spectral video camera was performed in terms of the sensor spectral sensitivity, linearity, spatial uniformity, noise and spatial alignment. The results indicate small deviation from ideal linear sensor response. Also, a small spatial non-uniformity and systematic shift exists between the channel images. However, images were observed to have high quality in term of noise. Spectral characterization showed that the sensor has good response in the 380-910 nm region with only some sensitivity limitations in the 715-740 nm range. We also evaluated the spectral reflectance estimation in 400-700 nm range using empirical regression methods and the Digital ColorChecker SG and ColorChecker charts. These experiments resulted in average ΔE00 color accuracy of 1.6 – 2.4 units, depending on the illuminant and estimation method.

Large Gamut Backlight for an LCD With Four Primaries

A small backlight unit having four LEDs of different colors is designed and fabricated. Traditionally, the backlight units are lit by white cold cathode fluorescent lamps or by white LEDs. Our backlight unit utilizes four monochromatic LEDs. LEDs are located at corners of the light guide. Outcoupling is accomplished using large period blazed-gratings. The master plate for the light guide is fabricated by laser lithography. The final lightguide is UV-casted on a PMMA plate using an electroplated nickel tool. Proposed backlight unit enlarges significantly the gamut of LCD, if the color filters of the LCD panel have been chosen appropriately. The brightness uniformity and the white balance of the backlight are analyzed by a fiber spectrometer. The brightness uniformity of the backlight is good, over 85%. White balance of the backlight should be further improved.

Additive colour mixing by surface relief gratings utilizing the power spectrum of a fluorescent lamp

Additive colour mixing produced by diffractive grating structures is studied. The gratings produce almost monochromatic primary colours to a selected viewing angle, providing thus a very large colour gamut. The colours inside the gamut are obtained by additive colour mixing in the reflected diffraction order. The amount of a single primary in the additive colour mixing within one colour pixel is determined by the area fraction of the corresponding grating. We demonstrated the concept by fabricating samples which appear white at 30° viewing angle when illuminated by 4000 K fluorescent lamp.

Diffractive parameric colors

A method of producing inkless parameric color pairs is studied. In this method, colors are formed additively using diffraction gratings with differing grating periods as primary colors. Gratings with different grating periods reflect different spectral radiance peaks of a fluorescent lamp to the desired viewing angle, according to the grating equation. Four spectral peaks of a 4000 K fluorescent lamp--red, green, cyan, and blue-are used as the primary colors. The colors are mixed additively by fixing the relative areas of different grating periods inside a pixel. With four primary colors it is possible to mix certain colors with different triplets of primary colors. Thus, it is theoretically possible to produce metameric colors. In this study, three parameric color pairs are fabricated using electron beam lithography, electroplating, and hot embossing. The radiance spectra of the color pairs are measured by spectroradiometer from hot-embossed plastic samples. The CIELAB DeltaE(ab) and CIEDE2000 color differences between radiance spectra of the color pairs are calculated. The CIEDE2000 color differences of color pairs are between 2.6 and 7.2 units in reference viewing conditions. The effects of viewing angle and different light sources are also evaluated. It is found that both the viewing angle and the light source have very strong influences on the color differences of the color pairs.

Diffractive Optics in Industry and Research - Novel Components for Optical Security Systems

Design and manufacturing of diffractive optical elements (DOEs) are presented. Mass replication methods for DOEs are explained including UV-replication, micro-injection moulding and reel-to-reel production. Novel applications of diffractive optics including spectroscopic surface relief gratings, antireflection surfaces, infrared light rejection gratings, light incoupling into thin waveguides, and additive diffractive colour mixing are presented.

Natural Vision Data File Format as a New Spectral Image Format for Biological Applications

Many kinds of spectral image formats are used for various applications, but there is still no existing standard format. Natural Vision data file format is one of the best possible candidates for the standard of spectral image format due to its flexibility to adapt to various kinds of existing image format and capacity to include information needed for each application. In biology, the analysis of huge datasets acquired by various techniques requires the use of specific databases. In order to be able to combine different data, defining a standard spectral image format that includes biological parameters is of prime importance. This paper describes an attempt to use Natural Vision data file format for spectral images related to biology and highlights the merits of Natural Vision data file format as an application oriented spectral image format.