Image Luminance Research Articles

Enhancement of image luminance resolution by imposing random jitter

Inspired by biological eyes, silicon retinas with pixel-level processing have been developed to achieve very high-speed and high-quality image processing. Due to the limitation on the fill factor and the dimension of a silicon chip, both spatial and luminance resolutions have to be kept low. For recovering fine images from a silicon retina with a lower resolution, the authors propose a neural network model and its electronic counterpart by imposing random jitter to the sensor and collecting temporal statistics of the firing neurons. Statistical analysis shows that the scheme can enhance resolution of an image and emphasize contrast edges present in the image. It is further proved that the enhancement in luminance resolution and sharpness is a trade-off between recovering bias and variance. Therefore, jitter intensity needs to be optimized by considering the luminance distribution. The simulations illustrate its effect on the fine detail reconstruction using the proposed scheme.

Robust contour reconstruction of red blood cells and parasites in the automated identification of the stages of malarial infection

We present a novel method for detecting malaria parasites and determining the stage of infection from digital images comprising red blood cells (RBCs). The proposed method is robust under varying conditions of image luminance, contrast and clumping of RBCs. Both strong and weak boundary edges of the RBCs and parasites are detected based on the similarity measure between local image neighborhoods and predefined edge filters. A rule-based algorithm is applied to link edge fragments to form closed contours of the RBCs and parasite regions, as well as to split clumps into constituent cells. A radial basis support vector machine determines the stage of infection from features extracted from each parasite region. The proposed method achieves 97% accuracy in cell segmentation and 86% accuracy in parasite detection when tested on a total of 530 digitally captured images of three species of malaria parasites: Plasmodium falciparum, Plasmodium yoelii and Plasmodium berghei.

44.3: Characterization of Motion Parallax on Multi‐view/Integral‐imaging Displays

AbstractMulti‐view and integral imaging displays have a significant feature that allows people to induce better stereopsis due to motion parallax. Base on the analysis of the mechanism, we propose characterization methods of the displays. Our methods evaluate change in luminance of stereoscopic images when observer's eye positions are displaced. The results show that our methods are good for showing smoothness of the motion parallax.

Fast panorama stitching for high-quality panoramic images on mobile phones

This paper addresses the problem of creating high-resolution and high-quality panoramic images from long image sequences with very different colors and luminance in source images. A fast stitching approach is proposed for combining a set of source images into a panoramic image using little memory, and implemented on mobile phones. In this approach, color correction reduces color differences of source images and balances colors and luminance in the whole image sequence, dynamic programming finds optimal seams in overlapping areas between adjacent images and merges them together, and image blending further smoothens color transitions and hides visible seams and stitching artifacts. A sequential panorama stitching procedure constructs panoramic images. The advantages include fast processing speed using dynamic programming for optimal seam finding, reducing memory needs by using the sequential panorama stitching, and improved quality of image labeling and blending due to the use of color correction. The approach has been tested with different image sequences and it works well on both indoor and outdoor scenes.

19.2: Adaptive Luminance and Saturation Control for RGBW OLED Displays

AbstractAn algorithm is discussed for adoptively adjusting the luminance and saturation of images for an RGBW OLED display. By considering image statistics, this algorithm significantly reduces the peak current per color channel and the peak display current while reducing luminance or saturation for only infrequently occurring images.

75.3: Is Brighter Always Better? The Effects of Display and Ambient Luminance on Preferences for Digital Signage

AbstractPreferred brightness may depend on many variables including image luminance and ambient illumination. To better understand the effects of these variables we asked observers to rate natural images according to their preferred brightness. Surprisingly, ratings plateaued at moderate luminance levels, and were only weakly influenced by ambient lighting.

Layered image representations and the perception of lightness

One of the fundamental issues in lightness perception concerns the structure of lightness representations. A central debate involves the role of layered image representations in the computation of surface lightness. Barrow & Tenenbaum (1978) suggested that the visual system performs an analysis in which the image is decomposed into a series of layered maps that represent the illumination, shape and lightness of surfaces in the image. More recently, a number of authors have questioned the role of layered image representations in the computation of surface lightness (Gilchrist et al., 1999; Adelson, 2000). We present a new class of lightness illusions that definitively demonstrate the role of layered image representations in the computation of surface lightness. We generated random patches of texture with a power spectrum that varies as 1/f^^n (n>2). The spatial frequency components were then summed with random phases and orientations. Three versions of each image were constructed with this seed image: a higher contrast (HC) image; an image in which the maximal luminance in the texture fell below the mean of the HC display (a dark texture); and an image in which the minimal luminance was above the mean luminance of the HC image (a light texture). A small circular central patch of the HC image was placed on the corresponding position on both the dark and light textures. Both HC targets appeared as homogeneous circular discs overlaid with a transparent layer. Observers matched the perceived lightness of the central HC patch on each background. Our results revealed the largest lightness illusion reported to date: the HC target on the light background appeared black, and the HC target on the dark background appeared white. We show that the contrast relationships between the target patch and the surround are critical in causing these effects, particularly the polarity relationships. These results demonstrate that layered image representations can play a critical role in determining perceived surface lightness.

The saliency of luminance and color (diagnostic and anti-diagnostic) in images

The saliency of luminance and color (diagnostic and anti-diagnostic) in images

Noise masking reveals channels for second-order letters

We investigate the channels underlying identification of second-order letters using a critical-band masking paradigm. We find that observers use a single 1–1.5 octave-wide channel for this task. This channel’s best spatial frequency (c/letter) did not change across different noise conditions (indicating the inability of observers to switch channels to improve signal-to-noise ratio) or across different letter sizes (indicating scale invariance), for a fixed carrier frequency (c/letter). However, the channel’s best spatial frequency does change with stimulus carrier frequency (both in c/letter); one is proportional to the other. Following Majaj et al. (Majaj, N. J., Pelli, D. G., Kurshan, P., & Palomares, M. (2002). The role of spatial frequency channels in letter identification. Vision Research, 42, 1165–1184), we define “stroke frequency” as the line frequency (strokes/deg) in the luminance image. That is, for luminance-defined letters, stroke frequency is the number of lines (strokes) across each letter divided by letter width. For second-order letters, letter texture stroke frequency is the number of carrier cycles (luminance lines) within the letter ink area divided by the letter width. Unlike the nonlinear dependence found for first-order letters (implying scale-dependent processing), for second-order letters the channel frequency is half the letter texture stroke frequency (suggesting scale-invariant processing).

Detecting faces in impoverished images

Abstract The ability to detect faces in images is of critical ecological significance. It is a pre-requisite for other important face perception tasks such as person identification, gender classification and affect analysis. Here we address the question of how the visual system classifies images into face and non-face patterns. We focus on face detection in impoverished images, which allow us to explore information thresholds required for different levels of performance. Our experimental results provide lower bounds on image resolution needed for reliable discrimination between face and non-face patterns and help characterize the nature of facial representations used by the visual system under degraded viewing conditions. Specifically, they enable an evaluation of the contribution of luminance contrast, image orientation and local context on face-detection performance. Research reported in this paper was supported in part by funds from the Defense Advanced Research Projects Agency and a Sloan fellowship for neuroscience to PS.

Computational modeling of non Fourier motion

We apply a computational model of biological motion processing [1,2] to a class of stimuli described by Taub et al [3]. In these, n translating sine waves, separated by 2pi/n radians but otherwise identical, are randomly sampled spatially to produce an nth order stimulus. For n > 1, the motion of these stimuli is non-Fourier. When n = 2 this non-Fourier motion is clearly visible to human observers. As n increases the direction discrimination threshold increases until, when n = 5, no reliable threshold can be measured [3]. We show that our computational model, an extension of the gradient approach, can accurately detect the direction of motion in the non-Fourier stimuli and that, as n increases, the accuracy with which the model detects the correct direction of motion is reduced. The modeling results concur with the psychophysical data. Importantly, the model, which acts directly on image luminance, detects non-Fourier motion without a preprocessing non-linearity (the hallmark of all other low-level approaches to the detection of non-Fourier motion). The most obvious explanation of how this might occur is that non-Fourier motion is specified by the spatiotemporal gradients within the motion sequences. We assess whether this is the case by measuring local spatial and temporal gradients and plotting these in the form of a gradient plot; a histogram where spatial gradient is shown on the x axis, temporal gradient on the y axis, and number of occurrences of spatial gradient/temporal gradient combinations is indicated on the z axis. This analysis shows that the gradients correctly indicating non-Fourier motion predominate within the stimuli when n = 2 and that this predominance reduces as n increases.

Color Breakup Reduction by 180 Hz Stencil-FSC Method in Large-Sized Color Filter-Less LCDs

Field-sequential color (FSC) is a high optical throughput technique for future green liquid crystal displays (LCDs). However, the FSC-LCD faces a lethal issue, color breakup (CBU) which degrades image clarity and prevents high level LCD-TV productions. We proposed the 180 Hz Stencil Field-Sequential-Color method to redistribute intensities of the three primary color field-images to suppress CBU. By applying local color-backlight-dimming technology to FSC-LCDs, a low resolution colorful backlight panel combined with a high resolution color filter-less LC panel generated a green-based multi-color field-image which showed the most image luminance in the first field. Therefore, residual red and blue field-image intensities were reduced and effectively suppressed CBU when compared to field-rate increasing methods. In addition, to further implement hardware, the number of backlight divisions of 32×24 and a proper Gaussian point spread function profile were optimized via simulations while considering CBU reduction and image fidelity. Using optimized hardware parameters, the CBU phenomenon was suppressed by 50% of traditional RGB driving in simulation and was demonstrated on a 120 Hz 46-inch MVA LCD-TV.

Measurement of High Sensitivity and Low Crosstalk of Zero-Space Microlens for 2.8- $\mu\hbox{m}$-Pitch Active Pixel Sensor

This paper describes the difference between normal microlenses and zero-space microlenses in image sensors. The investigation of both sensitivity and crosstalk has been implemented for normal microlenses and zero-space microlenses that are fabricated on a 2.8-μm pinned photodiode array of 640 (row) by 480 (column) based on an 0.18-μm -CMOS process. The simulation results show that the zero-space microlens technology increases the pixel sensitivity by about 75.61% and decreases the crosstalk by about 9.4% compared to the normal microlens technology. This paper presents the sensitivity analysis of both normal microlenses and zero-space microlenses based on the wafer test data from the Teradyne IP750, which is a special wafer test platform for CMOS sensors. The results of the statistical data of the wafer test show that the sensitivity of the zero-space microlenses has been improved by about 73.6% on the red pixel (69.6% on the green pixel and 76.3% on the blue pixel) compared with that of the normal microlenses. Using a similar statistical method, the crosstalk characteristics of both the zero-space microlenses and the normal microlenses have been measured as well. Compared with the normal microlenses, the testing results show that the crosstalk of green light in red light is reduced by about 7.244% and the crosstalk of blue light in red light is reduced by about 41.447% due to the use of the zero-space microlens technology. More importantly, this paper also provides the comparison and analysis of the real images taken by CMOS image sensors with the normal microlenses and the zero-space microlenses, respectively. From the comparison of image results, the image luminance of the zero-space microlenses is higher than that of the normal microlenses, and the image definition of the zero-space microlenses is clearer than that of the normal microlenses as well. So far, the silicon results show that the zero-space microlens technology is a better choice than the normal microlens technology for CMOS image sensors of a small-size pixel.

유색 스크린의 굴곡과 영상의 평균밝기를 고려한 프로젝터용 색 보정 기법

In this paper, we propose an algorithm both geometric correction using a grid point image and radiometric adaptive projection that dependent upon the luminance of the input image and that of the background. This method projects and captures the grid point image then calculates the geometrically corrected position by difference between the two images. Next, to compensate color, a corrected image is calculated by the ratio divided luminance of an input image by luminance of arbitrary surface. In addition, we found the scaling factor which controls the contrast to avoid clipping error. At this time, the scaling factor is dependent on mean image lightness when background is determined. Experimental results show that the proposed method achieves good performance and is able to reduce the perceived color clipping and artifacts, better approximating the projection on a white screen.

Visibility Evaluation Method with Luminance Image

Proposed in this paper is a visibility evaluation method applicable for any complicated situation. It is applicable, if a luminance image with a target is obtained, to any kind of targets, namely both luminous and reflective targets, to any shape of targets, to targets with non-uniform luminance, and to targets with any complicated luminous background. This method is based on the multi-channel model of our visual system and uses an orthogonal wavelet transform with symlet 6 as the mother wavelet. The method can generate a Visibility Evaluation Image from a luminance image with a target, based on the contrast sensitivity functions of various average luminances. VEI illustrates the visual edges of any objects in the luminance image. The value indicated in the VEI can be represented by using multiples of the threshold level and by using the subjective visibility levels. The VEI for a person with a specific visual performance can be generated if his/her contrast sensitivity functions are provided.

Improvement of Ringing Artifact Reduction Using a K-Means Method for Color Moving Pictures

This paper proposes an improved method that uses a K-means method to effectively reduce the ringing artifacts in a color moving picture. To apply this improved K-method, we set the number of groups for the process to two (K=2) in the three dimensional R, G, B color space. We then improved the R, G, B color value of all of the pixels by moving the current R, G, Bcolor value of each pixel to calculated center values, which reduced the ringing artifacts. The results were verified by calculating the overshoot and the slope of the light luminance around the edges of test images that had been processed by the new algorithm. We then compared the calculated results with the overshoot and slope of the light luminance of the unprocessed image.

A Quantitative Evaluation Method for Luminance Non-uniformity of a Large LED Backlight

This report describes a quantification method for luminance non-uniformity of a large LED backlight. In experiments described herein, participants subjectively evaluated artificial indistinct Mura images that simulated luminance non-uniformity of an LED backlight. We measured the luminance distribution of the Mura images. Then, the measured luminance distribution was converted into S-CIELAB, in which anisotropic properties of the spatial frequency response of human vision were considered. Subsequently, some indexes for the quantification model were extracted. We conducted multiple regression analyses using the subjective evaluation value and the index values obtained from measured luminance of Mura image. We proposed a quantification model consisting of four indexes: high and low luminance area, number of Mura edges, sum of Mura edge areas, and maximum luminance difference.

Relationship between thermal and luminance distributions in high-power lateral GaN/InGaN light-emitting diodes

The relationship between the thermal and luminance distributions in high-power lateral GaN/InGaN light-emitting diodes (LEDs) is demonstrated. By using a three-dimensional electrical circuit model and experimentally measured thermal and luminance images of the LED chips, it is shown that thermal and luminance distributions have close correlation and that uniform current density is essential to improve the thermal and luminance properties of LED chips.

An Adaptive Tone Mapping Algorithm for High Dynamic Range Images

A common task of tone mapping algorithms is to reproduce high dynamic range images (HDR) on low dynamic range (LDR) display devices such as printers and monitors. We present a new tone mapping algorithm for the display of HDR images that was inspired by the adaptive process of the human visual system. The proposed algorithm is based on center/surround Retinex processing. Our method has two novel aspects. The input luminance image is first compressed by a global tone mapping curve. The curvature of the compression curve is adapted locally based on the pseudo-Hilbert scan technique, so it can provide a better overall impression before the subsequent local processing. Second, the local details are enhanced according to a non-linear adaptive spatial filter (Gaussian filter), whose shape (filter variance) is adapted to the high-contrast edges of the image. The proposed method takes advantage of the properties of both global and local processing while overcoming their respective disadvantages. Therefore, the algorithm can preserve visibility and contrast impression of high dynamic range scenes in standard display devices. We tested the proposed method on a variety of HDR images and also compared it to previous research. The results indicated that our method was effective for displaying images with high visual quality.

Technique for Spatial Objects Shaping with Abrasive-Water Jet Controlled by Virtual Image Luminance

Technique for Spatial Objects Shaping with Abrasive-Water Jet Controlled by Virtual Image Luminance