One of the hottest introduction to image coloring

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One of the introduction to image color modification

a good printed picture gives people the feeling of being comfortable and natural, as realistic as witnessed on site. Good printing reproduction depends on good originals, but most of the light films or photo originals used in daily printing are often biased due to the limitations of environment or light when shooting. These color biased pictures are very different from our daily visual experience, such as purple skin color, green sky and so on. If these color biased pictures are printed directly without any processing, the effect is certainly not good. It can be seen that just like the original, it is often not the most ideal treatment method. A good designer will correct the color biased pictures, so that the final printing results can conform to the visual habits of the human eye

making the image look natural is the basic principle of image color modification. However, this is easier said than done. If you don't understand the printing principle, this requirement is often difficult to achieve. It is often seen that some inexperienced designers work very carefully with Photoshop in front of the screen, and spend a lot of time with pulse and voltage output control methods, thinking that they will get ideal pictures, but the printing results are disappointing, which is really a pity

the reason is that designers rely on screen effects to judge printing colors. Almost all screens have their own color deviation, which is just a matter of degree. The effect of looking at the same photo on different screens is often very different. Moreover, the screen is a kind of light source. After a long time, the human eye will have a natural adjustment effect and adapt to the color deviation of the screen, so the color judgment will lose objectivity, resulting in inconsistent color correction effects. Therefore, the screen is not an ideal tool to judge the printing color. To master professional color modification skills, the first thing is to understand the printing principle, understand the point combination of colors, and understand the point data of pictures. In this way, you will not be confused by the screen. Even if you work on another screen, you will also get a consistent and ideal color correction effect

if the above 1 cuts are normal, the correct color judgment must be made first, and the basis of judgment is the gray balance relationship of printing. The part that appears to be neutral gray on the screen. If it is not printed in gray, it means that it is a color biased picture. How to predict the result and the color of the picture before printing is the knowledge that designers need to master. There is nothing mysterious about this knowledge. As long as you understand the principle and practice, you can become familiar with it

theoretically, the same amount of CMY (cyan, magenta, yellow) ink can be mixed to produce neutral gray. (that is, 50c+50m+50y can produce 50% gray). However, the ink in the real world is limited by industrial production conditions, and the color rendering ability of CMY is different. Among them, magenta has the strongest color rendering ability, and cyan has the weakest color rendering ability. Therefore, equal amounts of CMY ink will not produce neutral gray (which will be reddish gray). To obtain neutral gray, we must increase the proportion of cyan (c) ink, which is the basic principle of printing gray balance

for example, to produce 50% neutral gray, the amount of green is 13% more than magenta, and the amount of magenta and yellow ink can be about the same. If you want to produce 30% neutral gray, you need green to be 9% more than magenta. The mixing proportion of neutral grey, magenta and cyan will be different in different degrees. Be especially careful in light gray parts, because human eyes are most sensitive to light color deviation. In different cases, the proportion of cyan and magenta can be referred to the attached table, and there is no doubt that the figure here is only a reference. In fact, different brands of inks can make the point proportion different from 2% to 5%. It's best to discuss with your printing factory and let them provide you with different proportions of cyan and magenta mixed with neutral gray for reference, which will be more accurate when making judgments

having neutral gray point data is equivalent to having a reference color ruler, so it is very convenient to judge the color deviation of the image. Just find out the part of the image that belongs to neutral gray, and use the color detection tool to display its point proportion in Photoshop. If the reading obtained matches the standard, it can be concluded that the image has no color deviation, otherwise the image will be corrected according to the part that exceeds or falls below the standard

source: printing art 188/August, 1999

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