The aim of this study is to investigate whether the Helmholtz-Kohlrausch effect exists among the images having various
luminance and chroma levels. Firstly, five images were selected. Then each image was adjusted to have 4 different
average CIECAM02 C and 5 different average CIECAM02 J. In total 20 test images were generated per each image for
the psychophysical experiment. The psychophysical experiment was done in a dark room using a LCD display. To
evaluate the overall perceived brightness of images a magnitude estimation method was used. Fifteen participants
evaluated the brightness of each image comparing with the reference image. As a result, participants tended to evaluate
the brightness higher as the average CIECAM02 J and also CIECAM02 C of the image increases proving the Helmholtz-
Kohlrausch effect in images.
The current study is aimed to propose a post-processing method for video enhancement by adopting a color-protection
technique. The color-protection intends to attenuate perceptible artifacts due to over-enhancements in visually sensitive
image regions such as low-chroma colors, including skin and gray objects. In addition, reducing the loss in color texture
caused by the out-of-color-gamut signals is also taken into account. Consequently, color reproducibility of video
sequences could be remarkably enhanced while the undesirable visual exaggerations are minimized.
The goal of this study is to evaluate the difference of the preferred hues of familiar objects between the color deficient
observer and the normal observer. Thirteen test color images were chosen covering fruit colors, natural scene and human
faces. It contained red, yellow, green, blue, purple and skin color. Two color deficient observer (deuteranomal) and two
normal observers were participated in this experiment. They controlled the YCC hue of the objects in the images to
obtain the most preferred and the most natural image. The selected images were analyzed using CIELAB values of each
pixel. Data analysis results showed that in the case of naturalness, both groups selected the similar hues for the most of
image, while, in the case of preference, the color deficient observer preferred more reddish or more greenish images.
Since the deuteranomalous observer has relatively week perception for red and green region, they may prefer more
reddish or greenish color. The color difference between natural hue and preferred hue of deuteranomal observer is bigger
than those of normal observer.
The effect of the level of transmission and surround luminance on image quality of transparent display is studied. The
images on the OLED transparent display were simulated on LCD monitor by adding background scene to the original
images. The psychophysical experiment was carried out on normal and simulated transparent displays under four levels
of surround luminance (dark, dim, average and bright) and four different levels of transmission (17, 52, 70 and 87%).
Four test images were selected for the psychophysical experiment. Fifteen subjects were participated in this experiment
and they were asked to answer the degree of preference of each image for each condition with 7-point Likert-scale. As
the result, it is found that the image quality of OLED transparent display deteriorates as the surround luminance
increases and the transmittance increases but lowering the monitor gamma can be helpful to increase the image quality.
This result suggests that image quality requirement for a transparent display is different from conventional opaque
YCbCr color space composed of luma and chominance components is preferred for its ease of image processing.
However the non-orthogonality between YCbCr components induces unwanted perceived chroma change as controlling
luma values. In this study, a new method was designed for the unwanted chroma change compensation generated by
luma change. For six different YCC_hue angles, data points named ‘Original data’ generated with uniformly distributed
luma and Cb, Cr values. Then the weight values were applied to luma values of ‘Original data’ set resulting in ‘Test
data’ set followed by ‘new YCC_chroma’ calculation having miminum CIECAM02 ΔC between original and test data
for ‘Test data’ set. Finally mathematical model is developed to predict amount of YCC_chroma values to compensate
CIECAM02 chroma changes. This model implemented for luma controlling algorithm having constant perceived
chroma. The performance was tested numerically using data points and images. After compensation the result is
improved 51.69% than that before compensation when CIECAM02 Δ C between ‘Original data’ and ‘Test data’ after
compensation is compared. When new model is applied to test images, there is 32.03% improvement.
The YCbCr color space in BT.709 suffers the image quality deterioration by color difference signal sub-sampling though
reducing the number of signals are quite important issue for future television system. For the future television systems,
such as UHDTV and 3DTV, new color encoding space is required which can encode large color gamut and result in
good image quality even after color difference signal sub-sampling. In this study, two approaches i.e. following human
visual system (CIECAM02) and using new sets of wide color gamut primaries are considered to design new color
encoding space. Various YCC color encoding spaces are designed and the sub-sampled image qualities are compared.
The result shows that using the opponent color signals in simplified-CIECAM02 as YCC space has the best image
quality. Also it is shown that using wide color gamut primaries can improve the sub-sampled image quality significantly
than the current encoding color space for HDTV.
We present a collection of principles to compare two sets
of color primaries for wide gamut displays. A new, algorithmic threedimensional
method to find optimal color primaries both for threeprimary
and multiprimary displays is described. The method was
implemented in a computer program. The resulting optimal color
primary sets are discussed. We show that two-dimensional methods
to find optimal color primaries by using a chromaticity diagram are
inferior to three-dimensional optimization techniques that include luminance
This paper proposes a framework of colour preference control to satisfy the consumer's colour related emotion. A colour
harmony algorithm based on two-colour combinations is developed for displaying the images with several complementary colour pairs as the relationship of two-colour combination. The colours of pixels belonging to complementary colour areas in HSV colour space are shifted toward the target hue colours and there is no colour change for the other pixels. According to the developed technique, dynamic emotions by the proposed hue conversion can be improved and the controlled output image shows improved colour emotions in the preference of the human viewer. The psychophysical experiments are conducted to investigate the optimal model parameters to produce the most pleasant image to the users in the respect of colour emotions.
We develop a methodology to find the optimal memory color (colors of familiar objects) boundary in YCbCr color space and a local image adjustment technique called preferred color reproduction (PCR) to improve image quality. The optimal memory color boundary covers most familiar object colors taken under various viewing conditions. The PCR algorithm is developed based on the idea that colors of familiar objects (memory colors) are key factors in judging the naturalness of an image. The PCR algorithm is applied to pixels detected as having a memory color. Memory color detection is conducted using color information by checking if an input color is inside the predetermined memory color boundary. The PCR algorithm transforms colors inside the memory color boundary to be shifted toward the boundary of constant interval in the center. The PCR algorithm is applied to skin colors, and psychophysical experiments using real images were conducted to determine the best parameters for the algorithm resulting in the most preferred image.
Design principles are formulated to develop visually optimal multiprimary subpixel architectures. Two new hexagonal subpixel architectures optimized for multiprimary color displays are shown, each designed according to these principles. These new multiprimary pixel architectures are considered to be useful to eliminate the color fringe artifact. They are expected to yield images of better visual quality than previous three primary color architectures including the RGB stripe architecture. A new image rendering method is also formulated for multiprimary subpixel architectures. This method can be used with and without subpixel rendering. An error function is defined enabling proper chromaticity reproduction and enhanced luminance resolution.
The image processor in digital TV has started to play an important role due to the customers' growing desire for higher quality image. The customers want more vivid and natural images without any visual artifact. Image processing techniques are to meet customers' needs in spite of the physical limitation of the panel. In this paper, developments in image processing techniques for DTV in conjunction with developments in display technologies at Samsung R and D are reviewed. The introduced algorithms cover techniques required to solve the problems caused by the characteristics of the panel itself and techniques for enhancing the image quality of input signals optimized for the panel and human visual characteristics.
The preferred skin color reproduction algorithm is developed for the mobile display especially for a portrait image with one person as a main object occupying most of the screen. According to the developed technique, the skin area in an image is detected using color value of each pixel in YCbCr color space. The skin color boundary is defined as a quadrangle in Cb-Cr plane. The colors of pixels belonging to skin area are shifted toward the preferred colors while there is no color change for the other pixels. The psychophysical experiments are conducted to investigate the optimal model parameters providing the most pleasant image to the users. Then, the performance of developed algorithm is tested using the optimal parameters. The result shows that for more than 95% cases, the observers prefer the images treated with the developed algorithm compared to the original image. It is believed that the developed algorithm can be applied to the mobile application to improve the image quality regardless the input sources.
The theoretical approach is introduced to design the optimal chromaticities for primaries of a display with a given size of triangular color gamut in xy-plane. Optimal primaries are defined as a set of chromaticities of red, green and blue primaries with fixed white point that most optimally satisfying four criteria, i.e. gamut size, gamut shape, coverage of object colors and hue of the primaries, in the visually uniform color space, CIECAM02. It is assumed that the optimal gamut should cover that of sRGB and have similar maximum chroma for each hue. The number of SOCS data located outside the gamut is used as a criterion to judge the coverage of object colors. Also it is set the hues of primaries to be close to those of sRGB. The simulation results showed that the optimal primaries for 85% of NTSC area have similar points with sRGB for red and blue, and green primary is located in between sRGB and NTSC. For 100% of NTSC area, the optimal chromaticities are located near those of NTSC for red and green and that of sRGB for blue.
Experiments were conducted to investigate colour appearance under mesopic vision. Lightness, colourfulness and hue observations of 40 test colours were accumulated for eight phases with four different luminance levels covering 0.1 to 90 cd/m2 and two different stimulus sizes corresponding to viewing angles of 2° and 10° using the magnitude estimation method. The psychophysical effects of luminance level and patch size on colour appearance were investigated and the role of the rods under mesopic vision was explored.
Two sets of color appearance data were accumulated for investigating the difference between LCD projector and LCD self-luminous colors. Psychophysical experiments were conducted using magnitude estimation methods. These colors were viewed against different neutral backgrounds. These data sets were used to test the performance of five color appearance models (CIECAM97s, Hunt94, LLAB, RLAB and CIELAB together with two most recently proposed revisions of CIECAM97s: Fairchild and FC).
In this study, the characterization method for a typical desktop LCD color projector is reviewed. Measurements were made with a spectroradiometer to establish the additivity of the primaries, inter-channel dependence, color gamut, tone scale, contrast, spatial non-uniformity, temporal stability and viewing angle variation. In the case of tone characterization, LCD projectors show S-shaped curve between input digital values and output luminance unlike the conventional CRT monitor represented by a power function. Mathematical models to predict the S-shaped electro-optical transfer function have been empirically derive.d Four mathematical models including PLCC, GOG, S-Curve Model I and II were compared for their accuracy in predicting the colors generated by the display for arbitrary signal inputs. It is proven that the newly derived S-Curve Model I and II work successfully for an LCD projector.