Dot-matrix holograms contain diffraction gratings with different periods and orientations. Grating parameters (period and orintation) are calculated according to input data, which is graphic raster file. Traditionally image uses additive color model RGB, which involves limited color range. To increase color range International Illumination Commission (ICI) color model is considered. In this paper methods for calculating the parameters of diffraction gratings with different periods and orientations for ICI graphic files are investigated and analyzed. Result of the calculation dot-matrix hologram is a set of diffraction gratings. Color, displayed from hologram pixel, should be close to the color of the corresponding pixel of the input image. The following grating parameters are used to set hologram pixel color: The period of the holographic grating; Angular orientation of the holographic grating; Relief parameters - depth and profile type.
Although color acquisition using the RGB system is widely used in many areas, and the RGB system can be used display a wide range of colors, but it still can not cover all possible colors in the ICI chart. To expand color range reproduction by means
Computer Optics and Nanophotonics / L.A. Nayden, I.K. Tsyganov, S.B. Odinokov of diffraction gratings, method of color reconstructing in the ICI colorimetric system (1931) is used. The ICI and RGB colormaps are illustrated on Fig. 1.
Any three different diffraction dots representing three different wavelengths can form any color within the ICI diagram. X, Y, Z are the color coordinates, the vertices of the triangle in which the color is formed. According to the ICI theory, as shown in Fig. 2, the required color is the color having the coordinates x0 y0 and the intensity V0 denoted by [(x0, y0), Y0]. The three selected points have the following coordinates (x1 y1), (x2 y2), (x3 y3). The intensity of the diffracted light at these thre e points of light will be denoted by Y1, Y2, Y3. Then, knowing the coordinates of these points, through non-complex calculations, one can come to the definition of the required coordinate.
The intensity of the diffracted radiation (shown in Fig. 3.) depends on the number of points with diffraction gratings, the more points, the greater the intensity, and, consequently, the brightness of the pixel.
The required number of points of each previously defined color depends on the geometric distance in the ICI color chart between the desired color and the three primary colors. In this case, the intensity of the reflected light corresponds to the number of points used to represent the primary color.
Selecting a sufficient number of diffraction points that create colors close to the border of the ICI color chart, almost all the colors located inside the diagram can be easily display by combining different diffraction pixels. Representation of the image in the ICI colormap system allows to provide a larger color spectrum than RGB.