If a worker wants to do something good, he must first sharpen his tools. Because of the color pictures we make, it is ultimately presented in a printed manner. Understanding the principles, characteristics, and limitations of the color printing process is very important for the production of high-quality pictures. Without this knowledge, it would be like sailing without a compass. All relying on speculation, it may reach its destination, and it may never reach it.
Off-line offset printing technology is now used to express colors in the shape and arrangement of dots. Common dot shapes include dots, squares, and ellipses, and the dot size is expressed in hundredths. In general, the minimum point printed on a four-color offset printer is 2%, and the maximum is 85%. These numbers represent the proportion of ink coverage in a single dot area. Why is the maximum area of ​​dots not 100%? This is due to the size of the printing dots and is also affected by two other factors. The first factor is the total amount of ink in the printing grid (ie, the amount of four-color ink that can be tolerated per unit area). The second factor is "dotgain". Due to the excessive supply of ink, the paper will be excessively wetted, causing problems in production, such as affecting registration due to paper deformation, the total amount of four-color printing is not more than 350%, so the maximum value of individual printing dots It will not be more than 85%.
The dot gain value is the result of the interaction of the ink characteristics, the printing pressure, and the ink receiving ability of the paper. The factors of printing pressure and paper are more decisive. In general, high-quality light flour paper has a smaller dotgain (about 15% to 20%), and the dotgain of newsprint can be large (approximately 25% to 35%), so that the same set of film is used to make the zinc plate and print on different papers. , color effects can be very different. Relatively speaking, printing pressure is a variable that can be grasped by the printing factory. Some printing companies even set the average outlet value of each printing press under normal conditions to be used as production quality control. Since the dotgain will affect the final color effect of the picture, it is a variable that we need to take into account when we do the image correction.
Before the color correction of an image, there is usually a review step, which is to see if the level of the scanned image is normal. Most of the pictures can be divided into three parts: light part (light part), middle part and dark part (dark part). These three parts constitute the light and dark levels of the entire picture. The troubles of color correction and pitfalls in beginners are excessive attention to color and ignorance of levels. In fact, whether or not pictures are expressive, and the level is often the key factor.
To grasp the changes in levels, we need to start with the light and dark positions. The light position is the smallest part of the total CMYK points in the picture. The dark bit is the largest part of the total CMYK points. These two places are the start and end of the picture hierarchy. To make it easier to understand, imagine the picture as a room. The light level is the light source in the room. If the light source is bright, the whole house will be brightened. If the light source is dark, the whole house will be completely dimmed; if the light source is blue In color, every part of the house will also have a blue hue. Therefore, whether the light spot value is correct or not determines the level and color cast of the entire picture. The common light position value is 5C3M3Y or 4C2M2Y. If the light position deviates from these values, it is almost certain that the level and hue of the entire picture need to be corrected.
In the same way, if the dark position value is misplaced, the expressiveness of the entire picture will be greatly reduced. If the dark position is too deep (the value is too large), the details of the dark part will not be represented. It will become black and the dark position will be insufficient. The black will turn grey and it will look unnatural and unrealistic. .
Choosing the correct light position and dark position is the basis for the full expression of the image expression. Through understanding the meaning behind the values ​​of the light position and the dark position, no matter what the picture is, what kind of screen is selected, it can also be handled with care. High quality color pictures.
Off-line offset printing technology is now used to express colors in the shape and arrangement of dots. Common dot shapes include dots, squares, and ellipses, and the dot size is expressed in hundredths. In general, the minimum point printed on a four-color offset printer is 2%, and the maximum is 85%. These numbers represent the proportion of ink coverage in a single dot area. Why is the maximum area of ​​dots not 100%? This is due to the size of the printing dots and is also affected by two other factors. The first factor is the total amount of ink in the printing grid (ie, the amount of four-color ink that can be tolerated per unit area). The second factor is "dotgain". Due to the excessive supply of ink, the paper will be excessively wetted, causing problems in production, such as affecting registration due to paper deformation, the total amount of four-color printing is not more than 350%, so the maximum value of individual printing dots It will not be more than 85%.
The dot gain value is the result of the interaction of the ink characteristics, the printing pressure, and the ink receiving ability of the paper. The factors of printing pressure and paper are more decisive. In general, high-quality light flour paper has a smaller dotgain (about 15% to 20%), and the dotgain of newsprint can be large (approximately 25% to 35%), so that the same set of film is used to make the zinc plate and print on different papers. , color effects can be very different. Relatively speaking, printing pressure is a variable that can be grasped by the printing factory. Some printing companies even set the average outlet value of each printing press under normal conditions to be used as production quality control. Since the dotgain will affect the final color effect of the picture, it is a variable that we need to take into account when we do the image correction.
Before the color correction of an image, there is usually a review step, which is to see if the level of the scanned image is normal. Most of the pictures can be divided into three parts: light part (light part), middle part and dark part (dark part). These three parts constitute the light and dark levels of the entire picture. The troubles of color correction and pitfalls in beginners are excessive attention to color and ignorance of levels. In fact, whether or not pictures are expressive, and the level is often the key factor.
To grasp the changes in levels, we need to start with the light and dark positions. The light position is the smallest part of the total CMYK points in the picture. The dark bit is the largest part of the total CMYK points. These two places are the start and end of the picture hierarchy. To make it easier to understand, imagine the picture as a room. The light level is the light source in the room. If the light source is bright, the whole house will be brightened. If the light source is dark, the whole house will be completely dimmed; if the light source is blue In color, every part of the house will also have a blue hue. Therefore, whether the light spot value is correct or not determines the level and color cast of the entire picture. The common light position value is 5C3M3Y or 4C2M2Y. If the light position deviates from these values, it is almost certain that the level and hue of the entire picture need to be corrected.
In the same way, if the dark position value is misplaced, the expressiveness of the entire picture will be greatly reduced. If the dark position is too deep (the value is too large), the details of the dark part will not be represented. It will become black and the dark position will be insufficient. The black will turn grey and it will look unnatural and unrealistic. .
Choosing the correct light position and dark position is the basis for the full expression of the image expression. Through understanding the meaning behind the values ​​of the light position and the dark position, no matter what the picture is, what kind of screen is selected, it can also be handled with care. High quality color pictures.
Dafa Aluminum Industry Co., Ltd. , http://www.hnaluminiumfoil.com