Photoshop is an indispensable image processing software in the prepress area. The level of use of Photoshop software directly affects the effect of flat products. As far as newspaper printing is concerned, the quality of image processing directly affects the quality of a newspaper. Especially in recent years, the rapid development of color newspapers, and the requirement for image processing in newspaper printing has become higher. It is absolutely necessary for personnel to have a deeper understanding and learning of Photoshop.
The quality of image processing has a lot to do with one's artistic accomplishment and experience accumulation. We must constantly learn good methods, absorb other people's experiences, and strive to improve our self-cultivation in order to gradually improve ourselves. Image processing level.
First, adjust the monitor
WYSIWYG is the ideal realm that the prepress field has been pursuing at present, but in actual work, due to the differences in the hardware itself, changes in the hardware settings, and the instability of the printing process, it is difficult for people to achieve the effect of screen display. The effect after printing. Our job is to make the screen display as close to the final print as possible and minimize the visual error of the two.
The specific method is: under the premise of relatively stable printing process, scanning the image to form an electronic file, the final image of the Wenbo after the printing and printing, we use the printed product (newspaper) to adjust the screen display. Use Photoshop to open the image of the electronic file and compare the newspaper for correction. Go to the control panel and open the Adobe Gamma correction program. Follow the prompts to complete the operation step by step. First, adjust the contrast to the maximum value, adjust the brightness, and make the middle block in the brightness display test block as dark as possible with the pure frame color. Then compare the image on the newspaper and the electronic file on the screen, adjust the total gamma value, and use the hierarchical display of the dark area of ​​the electronic document to be basically the same as the image on the newspaper, and then carefully observe the on-screen image and whether the printed image is colored Differences, if any, must be corrected for display colors, point-by-point channel corrections, and red, green, and blue light gamma buttons, respectively. It is worth mentioning here is that when adjusting the color, we must fully understand the additive principle of colored light and the principle of subtractive color of the color material, as well as the principle of complementary colors, in order to accurately correct the consistency of the screen display and print, not blindly adjust .
Second, adjust the scanner
Many people think that Photoshop software can make great adjustments to the image, so the importance of the scanner correction is ignored, it is not true, if the scanner is not adjusted in the best condition, not only the image has the possibility of color cast, but also lost The image level cannot be increased again in Photoshop adjustments.
Correction method: The general scanner is equipped with a gray scale and a color ladder for correcting the scanner. After resetting the various settings of the scanner, the scanner feet are placed in the scanner to form an image, and the gray scale is checked. In part, the first rung RGB value should be R=G=B=250, the rung 21 value should be R=G=B=5-10, and the rung 11 rung should be R=G=B. = 128, if the data of these steps differ greatly from the above data, we set the scanner's light, medium, and dark tone data and rescan to make the data of the gray ladder basically consistent with the data above. The difference between R, G, and B values ​​is large, indicating that the gray balance is distorted (ie, the scanner has a color shift), and the color data should be corrected for each channel so that the values ​​of R, G, and B on each rung are basically the same. In this way, the level and color shift of the scanner are basically corrected. In this state, image scanning can be performed. The calibration of the scanner must be carried out on a regular basis so that the color cast is reduced and the level reproduction is complete.
Third, set the color separation parameters
During color image scanning, we advocate the use of RGB mode for scanning. This can accurately determine the white and black fields of the picture. When adjusting, each color version can compensate each other, which is conducive to the realization of gray balance. In addition, the RGB mode file is about 1/3 smaller than the CMYK mode file, and when performing various processes, the speed is faster. After the basic adjustment is completed, we convert the RGB mode to the CMYK mode. This conversion process is completely based on our color separation parameters. Different color separation parameters are set, and they have a great influence on the final printed matter.
Setting method: Select "File\Color Settings\CMYK" and the CMYK Settings dialog box appears.
1 The setting of outlet expansion rate: The expansion of outlets depends entirely on the characteristics of the inks we use and the printing characteristics of newsprint. The high-speed printing of rotation requires that the ink particle size cannot be too large and the liquidity is better, otherwise it will lead to an increase in the dot gain rate. According to the domestic situation, we use newsprint paper that is not coated paper. The ink characteristics are similar to those of the Swop standard. Therefore, we chose the ink as the standard of Swop (Newsprint), with the dot gain rate between 28% and 40%, and different printing. The data of the plant is quite different. Under the premise of stable printing, after long-term tracking and measurement of changes in this data, a reasonable network expansion rate suitable for the unit is determined.
2 Select the color separation type GCR and UCR, GCR is a gray component substitution (also known as non-color structure process), UCR is the removal of the background color. When printing on newsprint, the quality of the black version plays a decisive role in the entire printing process. For general manuscripts, we recommend using GCR, special manuscripts, and UCR can be used when there are few ash components.
3 Set black tone: There are several different ratios of light/medium/heavy/maximum for the black tone curve to choose from. For some bright, concise, and smooth originals, you can select the None item without copying the black version. To express its transparent feeling. If we feel unsatisfied with the given black version level curve, we can also choose the Custom item to set the black curve, and we can set the length of the black version, the starting position of the gray component substitution, and the strength of the substitution.
4 Set the maximum ink volume of the black version. Different types of originals have different settings. The basis for this numerical setting is to ensure that the black field of the print is sufficient, with sufficient contrast, and conducive to the reproduction of layers. The traditional electricity distribution plate making process tends to make the black version of the skeleton. Generally, the black version is limited to 70%. We can use this data to set the black ink volume to about 70-80%. In addition, this value is The setting must depend on the setting of the total ink volume. Under the premise that the total ink volume meets the requirements, the black ink volume will be aggravated, which will facilitate the printing of high-speed web machines.
5 set the total amount of ink: because the printability of newsprint, and the high speed of rotary printing, the total amount of ink determines the amount can not be too high, from the perspective of data reports abroad, the total amount of newsprint printing ink is generally controlled at 240-260% (The total sum of the four CMYK dots) is determined by each process. It depends entirely on the dot gain rate at the time of printing. If the dots are enlarged during printing, the value must be reduced (but not less than 240). %)), otherwise the dark field part will stick to death, and the level of dark tone loss will be serious. If the dot enlargement is basically normal, you can increase the value appropriately (but not more than 280%) to ensure that the black field is dark enough to fully express the dark tone of the region, which is conducive to the reproduction of the entire tone. However, this value cannot be unlimited. Increase, otherwise it is not conducive to the improvement of printing speed, will expose a lot of printing problems.
Fourth, conscious compensation for tone adjustment
As mentioned earlier, due to the large dot gain rate in newsprint printing, the high speed of rotary printing determines that we cannot use a larger total amount of ink. Therefore, in newsprint printing, the level tones that we can copy are short, and it is impossible. To fully reproduce the level of the picture, we must ensure the reproduction of the important regional level in specific operations, and can be targeted to sacrifice some minor visual insensitivity, and the effect on the picture effect is not very large. Due to the enlargement of outlets, it is difficult to reproduce dark areas at the middle of the hierarchy. For manuscripts rich in medium and dark areas, under the premise of ensuring the density of black fields, the darkened network values ​​(adjusted using hierarchical curves) are reduced, and the darker levels are adjusted. Transferred to the intermediate tone, this effectively compensates for the tone level and guarantees the reproduction of the level of the area. Similarly, for the manuscript with a large area of ​​bright-sounding areas and a rich layer of shallow-keyed levels, we must also appropriately increase the number of sites of the white field. Values, bright copy more thick, so that the tone of the regional level shift to the shallow tone, effectively compensate for the loss of 2% below the sun in the print version of the network and the tone of the tone level of the loss, and ultimately achieve a visual sense of balance.
In short, the use of Photoshop software, you need to continue to accumulate experience to improve their artistic accomplishment, to be good at summing up the data in the work, to use the feedback results of the finished newspaper's picture effects, to re-examine the electronic files, to be aware of, gradually correct the parameters Settings. To be diligent in recording, to be good at analysis, and to have conditions, to do a good job of dataization and standardization work for a long period of time is of far-reaching significance for improving the level of image scanning and processing and improving the printing quality and the overall level of news newspapers.