Proc. SPIE. 9618, 2015 International Conference on Optical Instruments and Technology: Optical Systems and Modern Optoelectronic Instruments
KEYWORDS: Light emitting diodes, Visual process modeling, Spatial frequencies, Cameras, Digital cameras, 3D modeling, Image quality, Human vision and color perception, Contrast sensitivity, LED displays
Moiré pattern can be readily observed in the case of superimposing two periodic structures. Recently, Moiré pattern, which degrades the quality of an image, become unavoidable in many LED display and three-dimensional displays, which consist of regular structures. Therefore, a model of moiré which fit the character of human vision is important to solve the problem of image quality degradation. In this paper, we modified the the model of Moiré which proposed by Amidror to evaluate the color moiré fringes, which consider the property of human vision system of contrast sensitivity. From the modified model we conclude that moiré minimization could have two lattice form an certain angle. The experimental results show that moiré pattern are vivid when the angle is 0°, 15°, 20° and 45°. However, the spatial frequency of Moiré in 10°, 25°, 30° and 35° are fine in spatial domain. It is also reveal that changing angle is simple and effective in alleviating remarkably Moiré pattern.
The contrast of simple achromatic periodic patterns such as square-wave gratings is well defined and agrees with the Michelson contrast, but this is not so for chromatic contrast. It would be desirable to be able to determine the contrast of two colors for use in a general legibility metric. A method for determining the contrast of chromatic square-wave gratings, which is based on the CIE 1976 color difference formula, is proposed. In order to prove the feasibility, we first investigated the contrast sensitivity function of an achromatic grating using Michelson contrast for comparison through sets of psychophysical experiments keeping the mean luminance constant at 22.54 cd/m2. Further experiments compared the curve of contrast sensitivity function for red, green, and red-green chromatic square-wave grating in terms of the proposed formula and conventional formula in LMS cone contrast space, which is frequently used in calculating the contrast of color gratings. The results revealed that proposed method is helpful in calculating the contrast of chromatic square-wave gratings and reveals important physical meaning in measuring the contrast of chromatic gratings.
The effect of chromatic background on luminance contrast-sensitivity function (CSF) is studied. We selected three
background-grey, orange and yellow-green from CIE 17 color center. The mean luminance of these colors is
approximately equal. We use CRT monitor display the rectangular stripe. Every rectangular stripe has six spatial
frequencies (0.4, 1, 2, 3.5,7 and 14cpd) .The method of limits is used in the experiment, 5 observers, who have normal
vision and test of vision is all over 1.0, participated in the experiment. The results of experiment show that the luminance
contrast sensitivity on chromatic background is lower than the luminance contrast sensitivity under grey background.
Fitting results show that Movshon model is better than Barten model, especially for the chromatic background. Both of
the models have deviation in the high spatial frequency part.