Color image information input system

The image input system of the electronic color separation machine has two modes, one of which is a roller type point-by-point scanning method, that is, rotation and illumination optical system of an analysis roller with an attached document during photoelectric scanning of the electronic color separation machine. The lateral movement with the analysis head forms a helical scanning line, and each scanning line is again decomposed into a large number of image information units, pixels, in the heel circumferential direction. As shown in Figure 2.12. These pixels constitute the basic unit of the manuscript, which converts the different densities of the manuscript into light intensity, and thus converts it into the basis of analog electrical signals or digital signals that can perform various processes. The second method is to use the CCD plane scanning method, as shown in Figure 2.13, which attaches the original to the scanning platform and adopts line scanning or surface scanning similar to the video image to obtain the image information. Regardless of how different the scanning method is, the common components are shown in Figure 2.14. That is, the entire image information input system is mainly composed of a lighting system, a synchronization signal generation system, a scanning system, a photoelectric conversion system, and an A/D system.

Lighting system

The illumination system of the electronic color separation machine consists of a scanning light source, a light source feedback photoelectric stability control system, and a lighting power source.

One light source

All substances in the world, people can see through the auditorium their form, volume, quality and their location in space and their mutual relations, all thanks to the results of light lighting, that is, people simply know The objective world and conditions for transforming the objective world. Therefore, people in the printing industry regard the light source as the lifeblood. In an electronic color separation machine, the scanning light source determines the basis for image reproduction. It not only requires that the light source has high brightness and high stability, but also has the characteristics of a standard light source, so as to ensure the acquisition of correct image information. Therefore, the light source of the electronic color separation machine should meet the following conditions.

1. Spectrum

The spectrum of the light source refers to the distribution of the wavelength of the color light of different intensity in the light source. If the light emitted by the light source contains only part of the wavelength, it is called the line spectrum. If the light emitted by the light source contains all the colors of light, it is called continuous spectrum. In the electronic color separation machine, since the light source is the key to correctly reproduce the original color, the light source must be full spectrum, approximately daylight.

2. Color temperature

Color temperature means that if the light emitted by a light source has the same color as the standard black body at a certain temperature, the temperature of the standard black body is called the color temperature of the light source. Color temperature shows the characteristics of the light source radiation spectrum. The color temperature of the light source is 6000°K in the electronic color separation machine.

3. Color rendering

Color rendering refers to the degree of similarity of an object's colors under the illumination of a light source and a standard light source. The scanning light source of an electronic color separation machine requires its color rendering property to be greater than 90%.

4. Luminous efficiency

Luminous efficiency refers to the number of lumens emitted by a light source for each watt of power consumed. The luminous efficiency of the scanning light source of the electronic color separation machine should be not less than 30 lumens/watt.

5. The electronic color separation machine scans the light source, and also requires that its luminosity is stable, it is affected by the outside, the structure is simple, the volume is small, and the potential radiation is small.

According to the above conditions and a large number of experimental studies, the scanning light source of the electronic color separation machine is now mostly a xenon lamp or a bromine tungsten lamp.

Light source

The xenon lamp adopts a high-pressure short-arc xenon lamp, as shown in the arc pattern shown in Figure 2.15. The cathode part has high brightness, the anode part is small, the vertical pincene has the same illuminance in the horizontal direction, the color table has high display, and the color rendering index is above 95%. The power is mostly 150W, the luminous enthalpy rate is 30-50 lm/W, and the color temperature is about 6000K. However, its disadvantage is poor photometric stability, and it is vulnerable to external magnetic fields, internal pressure and environmental vibration. Therefore, photoelectric feedback is usually used in the electronic color separation machine. The method to keep the light level stable. The most typical method is as shown in Figure 2.16. When the xenon lamp is directed to the right end of the arm, a beam splitter made of two standard right-angle prisms glued to the right end of the arm, which reflects 80% of the light to the original. 10% light is transmitted to the photocell. If the intensity of the light emitted by the xenon lamp changes, the output voltage of the photovoltaic cell is changed and detected, and then the change voltage is amplified by the photoelectric feedforward circuit and used as a control signal for the preamplifier bias level of the light source. This compensates for the change in the intensity of the xenon light line so that the output of the preamplifier is not affected by the xenon lamp intensity change. When scanning a reflection draft, the principle is the same as in the transmissive manuscript.

2. Iodine tungsten lamp

Bromine tungsten lamp is an incandescent lamp with high luminous intensity. Due to the use of a bromine-tungsten cycle system, it can always maintain a high luminous flux. Its light intensity distribution is shown in Figure 2.17. The spectrum irradiated by the bromine tungsten lamp is a continuous spectrum, as shown in Figure 2.18. It has good color rendering and faithfully reproduces the color of the original. In the electronic color separation machine, a bromine-tungsten lamp having a luminous efficiency of 30 lumens/watt, a color temperature of 3200K, and a power of 100 watts is generally used, and the size is small and the use is convenient. The use of a general-purpose regulated power supply can keep the luminous intensity highly stable.

Second, the scanning system

The scanning system is a device that scans an image and is an inherent unit of various image input systems. It is divided into electronic optical scanning systems and mechanical scanning systems. The scanning system of the electronic color separation machine is a key component for realizing the raster decomposition of the original and obtaining the required information. Usually it consists of two parts: image information collection and separation.

1. Acquisition of image information

The collection of image information of the electronic color separation machine is also referred to as sampling. Through the scanning optical system, the scanning light source converges on the surface of the original and forms a spot with a size of about 1 mm, and the size of the spot is 0.01-0.03 mm. After the original document information is transmitted or reflected, it enters the scan head by the scanning optical system, as shown in Figure 2.19. The optical signal entering the scanning head determines the scanning accuracy through the shape and diameter of the selected light hole on the aperture wheel.

The scanning light on the aperture wheel is also composed of a main light hole and a virtual light hole, wherein the main light hole can transmit light, and the virtual light hole can reflect light. The aperture of a typical virtual aperture is about 2-5 times the aperture of the main aperture. The electronic color separation machine is provided with a plurality of scanning apertures for users to use in different precision scans.

The shape of the main light hole is both round and square. The selection of the light hole is related to the quality of the original document, the diameter of the scanning roller, the number of recording lines, and the zoom magnification. Generally, the original document is high in resolution and is used for enlargement. Therefore, the main light aperture used is small, and the reflective document is poor in definition, and it is mostly used for original size or reduction, and the aperture of the main aperture is large. Theoretically speaking, we hope that the smaller the main aperture is, the better, and the smaller the area that can be sampled on the original, and the higher the sampling resolution of the image. However, if the aperture is too small, the amount of collected light will be reduced, resulting in a weak electrical signal after conversion, which will reduce the signal-to-noise ratio of the image signal and cause image quality degradation after copying. Therefore, the minimum value of the main aperture in actual production is A lower limit.

There is a large range of reflective surfaces around the main light hole. This is the counterfeit virtual light hole. The range of the collected light is larger than that of the main light hole, so the sharpness of the collected light is poor, and the represented pixel signal is also ambiguous compared to the signal of the main aperture pixel, which is called “virtual light signal”. The virtual light signal is used for The subtle level of emphasis on the signal of each channel.

In short, the function of the optical aperture of any kind of color separation machine is (1) to transmit the collected optical signal through a part to form a main signal; and (2) to reflect the other part of the collected optical signal to form a virtual optical signal.