Image scaling

In actual social cattle activities, the size and shape of prints are varied and varied. It is almost different from the size of the original, so the size of the original must be changed in the color reproduction process to meet the production needs. The electronic color separation machine has an image scaling function suitable for a certain range irrespective of the model, and the accuracy is increasingly improved.

First, the basic principle of image scaling

The scaling of the image is done in the electronic color separation machine by a part called a proportional computer. The image information accepted by the scale computer is different from the image processing system of the electronic color separation machine, and is divided into two kinds of digital image information and analog image information. However, they are all signals that have undergone various image corrections such as color correction, gradation correction, black edition calculation, under color removal, and subtle level enhancement. The scaling of the image size is mainly solved in the scale computer. Since the size of the electronic color image is controlled by a digital computer, the size change is flexible and the accuracy is high.

It can be seen from the foregoing. In photoengraving, the zooming of the image by the plate making camera is performed in parallel, and the lens recognizes the entire image, and image size conversion is achieved by scaling each unit area of ​​the image information. In the electronic color separation machine, the transmission of image information is serial. Therefore, the size transformation is based on the principle of image decomposition, that is, an image is decomposed into a number of tiny information units - pixels. Each pixel has a definite plane position (x, y) and density value (D). When the original pixels are transferred to the recording end for recombination, under the premise of ensuring that their mutual positions and density values ​​are not changed, the original size can be re-enlarged or reduced by changing the mutual setting of its pixels. The size change in the main scanning direction means that the distance between two pixels adjacent to the analysis end and the recording end changes. The size conversion in the direction of the scanning direction means that the analysis head and the recording head scan and record images with scanning lines of different pitches, respectively.

The color separation system of the electronic color separation machine has three transformation modes from its development:

1) Hierarchical transformation ratio, which means that there are only a few fixed zoom ratios. The size of the image is scaled by the size of the roller and the change of the transmission ratio of the lateral transmission. For example, the DS SG306 has three ratios of 1:1, 1:2, and 1:4.

2) Mechanical infinitely variable ratio: It refers to having more zoom ratios, using the principle of lever to change the main scanning direction by changing the main scanning line speed to complete the stepless transformation ratio in the main scanning direction, and implementing the stepless change of the direction of the auxiliary scanning by means of the screw principle. ratio. Such as Hell's C299.

3) Electronically infinitely variable ratio: It refers to the realization of the control of the position of each pixel by means of digital circuit technology or computing technology to achieve the dimensional transformation in the horizontal and vertical directions. Such as CROSFIELID company M656.

Among the three transformation methods, the electronic stepless transformation method is the most advanced and has high work efficiency, good quality, and easy operation.

In summary, the conversion of the scale of the electronic color separation machine is realized by the combination of the lateral movement constituted by the movement of the scanning head recording head and the longitudinal movement constituted by the rotation of the drum. Where the vertical dimension of the image changes, the longitudinal movement is completed because the scanning and recording drums are synchronized in longitudinal movement. Therefore, the two angles of rotation are equal. The vertical size conversion is achieved by sampling and recording the image signal at different speeds by means of a memory of a proportional computer. The ratio of the sampling pulse frequency to the recording pulse frequency is the magnification of the longitudinal electronic transformation ratio.

Due to the limitations of the working speed and capacity of the memory, the ratio of the scanning pulse frequency to the recording pulse frequency is in the range of 33.3% to 422%, but this range is too small for printing, so that in order to narrow the frequency range here Processing within the range of 20-2000% or even more wide-band range images usually uses several drums of different diameters on the machine for the user to choose.

The lateral size conversion of the image of the electronic color separation machine is accomplished by means of lateral movement, that is, the lateral size conversion is achieved by using different infeed speeds of the scanning head and the recording head. The ratio of the rotational speed of the transverse feed motor that actually drives the scanning and recording heads is the lateral scaling magnification (set the pitch of the two screws and the like). The motor rotation speed is controlled by the power supply frequency, that is, the lateral size conversion can be finally attributed to the ratio of the two pulse frequencies.

Second, the input signal preprocessing

The signal of the electronic color separation machine is digital in the proportional computer, and the scale conversion of the image information is achieved by transforming it. If a digital electronic color printer outputs a digital signal from a color computer, it can be directly used by a proportional computer. If analog electronic color separation, the signal needs to be preprocessed to make it a digital signal. That is, (1) the image is decomposed into discontinuous M×N pixels. (2) Quantify the range of density values ​​occupied by pixels and replace each quantization level with a number. The specific changes are as follows.

The electronic color separation machine continuously scans the image and obtains a continuously varying analog electrical signal after being transformed. The continuous signal acquires an instantaneous value at regular time intervals according to the sampling theorem, that is, it can obtain both complete image reproduction and The amount of data is smaller than the discrete value of the original image. The number of samples per unit of time is often referred to as the sampling frequency, which determines the amount of discrete data.

After sampling, the analog voltage value corresponding to each pixel is decomposed at a certain interval so that it is decomposed into N levels and each level is represented by a number, ie, quantized, so that the analog voltage signal of the image information is obtained. Become a digital signal.

After completing the sampling and quantification of the image signal, the image information of the manuscript is input into the proportional computer in the form of digital information.

Third, the proportion of the composition of the computer

The composition of the proportioning computer in the electronic color separation machine is shown in Figure 3.93. It consists of (1) clock signal generator, (2) frequency divider circuit, (3) analog-to-digital conversion circuit, (4) memory, (5) digital-to-analog conversion circuit, etc., wherein the clock signal generator is composed of a standard clock. Or random clock mode to generate the clock signal. In the standard clock mode, the clock signal is generated by a standard frequency generator. The most commonly used is a quartz oscillator. In the random clock mode, the clock signal is directly generated by the rotation of the drum, and a grating encoder coupled with the drum is often used. The clock signal controls the coordinated synchronization of the various parts of the proportional computer. The electronic color separation machine obtains two sets of synchronization pulse signals from the clock generator as control signals for image size conversion. Its vertical sync pulse controls the vertical size conversion circuit to achieve vertical size conversion, and the frame sync pulse controls the horizontal size conversion circuit to achieve horizontal size conversion. The function of the frequency dividing circuit is to decompose the horizontal synchronization pulse and the frame synchronization pulse into the analysis synchronization pulse and the recording synchronization pulse, and analyze the feed frequency and the recording feed frequency, and control the amplification ratio from the ratio of the analysis and the recording pulse (frequency). . This transforms the problem of image size conversion into a simple frequency ratio.

Fourth, horizontal size transformation

The lateral direction also refers to the scanning direction, that is, the scanning head and the recording head move in the horizontal direction. The scanning lines of the scanning head and the original are longitudinally arranged. When the ratio is changed, that is, when the recording head performs exposure recording at the recording end, it needs to be changed. The distance between the scanning lines arranged longitudinally on the color separation sheet.

In the electronic color separation machine, the pixels constituting the recorded image and the images composing the original correspond to each other. Similarly, if the number of scanning lines at the recording end is L/cm, and the conversion magnification is K, then the number of scanning lines at the analysis end is, that is, the ratio of lateral magnification of the electronic color separation machine is equal to the ratio of analysis scanning to recording scanning lines per unit length. The relationship between the number of scanning lines L and the lateral movement speed of the recording head and analysis head is:

Where: n is the drum speed

Vs is the lateral speed of the analysis head

Among them: VR is the lateral speed of the recording head

therefore

and

Among them: control pulse frequency for scanning head and recording head

It is the pulse feed equivalent of the scanning head and the recording head, that is, the distance by which a pulse signal is transposed to each side of the driving device.

The electronic color separation machine uses the screw to move laterally

and

Among them: Analysis and recording screw pitch.

Drive motor to screw reduction ratio

Drive motor pulse capacity, which is the number of pulses required to drive the motor one revolution.

When the design of the electronic color separation machine is completed, it is a fixed value, so the horizontal dimension transformation magnification K is:

Where: C is a constant.

From Equation 3-88, the horizontal scale conversion can be realized by changing the control pulse frequency during scanning and recording, and the horizontal transform magnification is equal to the ratio of the recording end control pulse frequency to the control end control pulse frequency.

Fifth, the vertical size transformation

Longitudinal size conversion refers to the use of pixel advance or delayed recording along the circumference of the drum to achieve a change in pitch between pixels. Its implementation method is shown in Figure 3.94. When the image is enlarged vertically, the vertical pitch between the pixels of the original pixel during recording needs to be changed, that is, the image information is first sampled at the sampling frequency f in the electronic color separation machine, and the acquired image information is obtained. The data is stored in a buffer memory, and then its image information is fetched from the buffer memory at a frequency f smaller than f, and then subjected to other transformation and then exposed on the color separation chip to realize the vertical magnification. In such a "quick taping" process, the conversion magnification K is:

When the image is reduced, the same reason that only the frequency f taken out from the buffer is larger than the write frequency f, that is, the “slow mining quick” method is adopted, and the transformation magnification K is:

From the above analysis, it can be concluded that the size conversion of the electronic color separation machine can be purchased by changing the frequency of the control pulse. Therefore, the use of the same clock signal by the proportional computer can not only ensure the high accuracy of image size conversion, but also enable the size The transformation depends only on the ratio of the scanned and recorded frequencies.