A preview of some of the most interesting papers appearing in the
January 2009 issue of the Journal of the SID.
To obtain access to these articles on-line, please go to www.sid.org
Edited by Aris Silzars
John J. McCann
Università degli Studi Milano
Abstract — Intraocular glare and simultaneous contrast control appearance in high-dynamic-range (HDR) images. Unique test targets that simulate real images are described. These targetschange the HDR range by 500 times, without significantly changing the veiling glare on the retina. These targets also have a nearly constant simultaneous contrast. The range of appearances possible from HDR images with different average luminances were measured. The targets displayed a maximum luminance range of 5.4 log units. Using magnitude estimates (MagEst) of appearances, the relationship between luminance and lightness from white to black was measured. With one exception, only small changes in appearance with large changes in dynamic range were found. It was also found that appearance was scene-dependent. The same dark grays (MagEst = 10) were observed with luminances of 10, 4.2, 1.1, and 0.063, depending on the percentage of white area in the surround. Glare from more white increases the retinal luminance of the test areas. Simultaneous contrast counteracts glare by making the appearance range (white–black) with a much smaller range of luminances. Appearance is controlled by both the optical scattered light and the spatial processing. A single tone-scale function of luminance cannot describe appearance controlled by scatter and spatial processing.
If the global physical properties of glare are considered, a surround that is, on average, equal to the middle of the dynamic range is prefered. This can be achieved by making the surround 50% max and 50% min luminance. Experiments have shown that the spatial distribution of white in the surround affects the appearance. To approximate real images, the half-white–half-black areas in differently sized squares were distributed.
FIGURE 4 — Magnified view of two of 20 gray pairs of luminance patches. The left half (square A) has the same layout as the right (square B), rotated 90° counterclockwise. The gray areas in A have slightly different luminances, top and bottom. The gray areas in B have different luminances, left and right. The square surrounding areas are identical except for rotation. For each size there are equal numbers of min and max blocks.
Abstract — A simple additivity model is often used as a basic model for digital-display characterization. However, such a simple model cannot satisfy the needs of demanding color-management applications all the time. On the other hand, systematic sampling of the color space and 3-D interpolation is an expensive method in terms of measurement and computation time when precision is needed. An enhanced method to characterize the XYZ-to-RGB transform of a digital display is presented. This parametric method exploits the independence between the luminance variation of the electro-optic response and the colorimetric responses for certain display types. The model is generally applicable to digital displays, including 3-DMD projectors, single DMDs, CRTs, LCDs, etc., if the independence condition is satisfied. While the problem to solve is a 3-D–to–3-D transformation (from XYZ to RGB), the proposed parametric model is the composition of a 2-D transform followed by a 1-D transform. The 2-D transform manages the chromatic aspects and, in succession, the 1-D transform manages the luminance variations. This parametric digital model is applicable in the field of color management, with the objective of characterizing digital displays and applying a reference look such as a film look.
The measurement data set includes two subsets:
• The "L" data subset: a gray ramp for the luminance-variation characterization.
• The "C" data subset: samples on three color planes for colorimetric characterization.
The "L" data subset covers the whole range of luminance variations, while the "C" data subset covers the whole range of chromatic variations. Figure 1 represents this data set. The black dashed line is the "L" data subset and the three colored planes are the "C" data subset.
FIGURE 1 — Characterization dataset.
Abstract — Many applications, such as AmbiLight TV and atmosphere creation with dynamic light, generate colored light that changes gradually from one color to another. However, there is not much scientific knowledge on how to create suitable color transitions. This study investigates what is perceptually the most optimal way to create a temporal color transition between two colors. The first experiment measured the ability to distinguish between two temporal color transitions. The reference transition was a linear interpolation between two colors in CIELab, the test transitions were arcs defined in different planes going through the linear transition. Discrimination thresholds ranged between 2.5 and 12.5 ΔEab, depending on the color pair, direction, and duration of the transition. In the second experiment, severalperceptually different color transitions were compared. The most preferred transitions were a linear transition in CIELab and a linear transition in RGB. The results suggest that it is possible to design a general algorithm for temporal color transitions that is appreciated by human observers, independent of color pair and application.
The test transitions were arcs defined in one of two planes: (1) the plane through start and end color parallel to the lightness axis, called the lightness plane and (2) the plane through start and end color perpendicular to the first plane, called the chromaticity plane [see Fig.1(a)]. The arcs were defined by three points: the start color, the end color, and a color in the corresponding plane at a distance D from the color halfway between the start and end color.
FIGURE 1 — (a) Examples of the reference transition (black line) and the test transitions with direction L+ (red arc), L– (green arc),Cin (magenta arc), and Cout (blue arc). (b) Projection of the reference transition and test transitions Cin and Cout on the ab plane for each color pair.
Dai Nippon Printing Co., Ltd.
Abstract — Soft proofing, which can confirm the color reproduction of printed matter on a monitor, is coming into wide use in the field of graphic arts. However, there is a problem in that the color on the monitor looks different from that of printed matter, even though the L*a*b* value of the monitor's white point has been adjusted to that of the paper by using a spectroradiometer. After the color rendition of an LCD is visually adjusted to that of the paper, the measured color of the LCD shows color with L*a*b* values corresponding to a more greenish-blue white than that of paper. For CRTs, this corresponds to a more bluish-white. In this paper, it was assumed that bright lines in the measured spectrums of the monitors and the illuminations spread to the next wavelength band by the optical systems of the spectroradiometer. To solve the problem, a method is proposed to enhance the bright line by using a three-tap digital filter. The effect of this method on two types of monitors under three types of illumination is also reported. After enhancing the bright lines, ΔE between the monitor and paper becomes smaller than that for the original one.
Figure 1 shows the device configuration used in this experiment. A color patch was displayed on the monitor. The brightness and hue of the color patch changes when the subjects click a button on the monitor. The target paper was placed next to the color patch on the surface of the monitor. The subjects observed the color patch and target paper from a 50-cm distance. The spectroradiometer was placed in the same location as the subjects.
FIGURE 1 — Configuration of device used in the visual color-matching experiment.
Wonbok Lee (SID Student Member)
University of California
Abstract — A 1-D LED-backlight-scanning technique and a 2-D local-dimming technique for large LCD TVs are presented. These techniques not only reduce the motion-blur artifacts by means of impulse representation of images in video, but also increase the static contrast ratio by means of local dimming in the image(s). Both techniques exploit a unique feature of an LED backlight in large LCD TVs in which the whole panel is divided into a pre-defined number of regions such that the luminance in each region is independently controllable. The proposed techniques are implemented in a FPGA and demonstrated on a 40-in. LCD TV. Measurement results show that the proposed techniques significantly reduce the motion-blur artifacts, enhance the static contrast ratio by about 3x, and reduce the power consumption by 10% on average.
Figure 5 shows some sample responses of the HVS. When the flash-light stimuli with a fixed intensity but with different durations are presented under a dark-adapted condition, the HVS responds with a certain duration (called visual persistence) which is 10–100x longer than the duration of the flashed light in the millisecond range. Therefore, the HVS converts the impulse-type image display of CRTs which lasts about 70 μsec to a maximum of 7 msec of light perception. Therefore, under the typical refresh rate of 60 Hz, a screen image on a CRT will be perceived as non-overlapping. Consequently, motion blur does not occur in CRT monitors. All the impulse-type image-display techniques for motion-blur reduction are based on this understanding of the motion-blur phenomenon and how it can be eliminated.
FIGURE 5 — Sample responses in HVS when different flash-light stimuli (with varying duration) are given.
V. Bhatia (SID Member)
Abstract — Efficient and very-compact projectors embedded into mobile consumer-electronic devices, such as handsets, media players, gaming consoles, and GPS units, will enable new consumer use and industry business models. A keystone component for such projectors is a green laser that is commensurately efficient and compact. A synthetic green-laser architecture that can achieve efficiencies of 15% is described. The architecture consists of an infrared distributed Bragg reflector laser coupled into a second-harmonic-generation device for conversion to green.
Figure 1 illustrates the laser architecture. The output beam of the laser diode is coupled into a second-harmonic-generation (SHG) device through a pair of lenses. The first lens collimates the output beam, and the second lens focuses the beam down to a small spot size for coupling into the SHG with an angled facet to minimize back-reflected power.
FIGURE 1 — Illustration of green-laser architecture.
Vladimir Chigrinov (SID Fellow)
Hong Kong University ofScience and Technology
Abstract — Multistable electro-optical modes exist under certain conditions in ferroelectric liquid-crystal (FLC) cells, which means that any light-transmission level can be memorized after the driving voltage is switched off. The multistability is responsible for three new electro-optical modes with different shapes of the gray-scale curve that can be either S-shaped (double or single dependent upon the applied-voltage pulse sequence and boundary conditions) or V-shaped dependent upon boundary conditions and FLC cell parameters. The origin of these modes will be described.
Both the amplitude and the duration of the driving pulses can be varied to change the switching energy, which defines the memorized level of FLC-cell transmission in a multistable electro-optical response (Fig. 2). Therefore, any level of theFLC-cell transmission, intermediate between the maximum and the minimum transmissions, can be memorized after switching off the voltage pulses and short-circuiting of the cell electrodes.
FIGURE 2 — Light transmission (bottom curves) memorized by the multistable FLC cell on (a) the amplitude of 1-msec alternating driving pulses and (b) the duration of alternating driving pulses ranging from 250 to 50 μsec.
Eun Gi Heo
Abstract — The influence of the Xe (15%) and He (70%) fractions on the discharge and driving characteristics was compared in 50-in. full-HD plasma-display panels. The same improvement in the luminous efficacy was obtained when increasing either the Xe or He fraction. However, the discharge current with a high He fraction was smaller than that with a high Xe fraction. While the breakdown voltage was hardly influenced by an increase in the He fraction, it was significantly changed when increasing the Xe fraction. The formative andstatistical time lags were only slightly changed with a high He fraction, yet significantly increased with a high Xe fraction. In addition, the relatively low luminance and driving-margin characteristics with a high He fraction were compensated for by controlling the capacitance of the upper dielectric layer.
FIGURE 2 — (a) Changes in luminance and net power consumption and (b) corresponding luminous efficacy of 50-in. test panel relative to sustain voltage for three different gas conditions: Xe (11%) – He (50%) – Ne (case 1), Xe (11%) – He (70%) – Ne (case 2), and Xe (15%) – He (50%) – Ne (case 3).