Important adjustments for color prints before printing
Printed manuscripts require four-color electrical division for plate-making. Apple computer color separation manuscripts include reflective drafts (such as: color pictures, drafts, watercolors, oil paintings, Chinese paintings, new year paintings, gouache, etc.) and transmission drafts (such as: color reversal films (natural color positive films), color negative films, etc.) The lightness and darkness on the color negative manuscript is opposite to the original scene, and the colors are complementary to the original scene. For example, the opposite color of magenta complementary on the negative film is green; the opposite color of yellow complementary is blue-violet; and the complementary color of red is cyan. The lightness and darkness on the positive manuscript are the same as the original scene, and the colors are exactly the same as the original real scene.
The printed copy of the transmission manuscript is a visual image formed under the action of transmitted light. The reflective manuscript is a visual image formed by the reflection of the manuscript under the illumination of a light source.
The tone of the printed matter is that the colors are classified according to lightness and darkness. The reproduction of printed products should achieve color restoration, tone restoration, texture restoration, and clarity restoration. Color reproduction means that the hue is accurate, and the printed product reproduces the true and perfect color of the original without discoloration and noise.
The ideal tone restoration means that the tone on the manuscript is restored "faithfully" on the printed product to meet the requirements for copying the manuscript. Since the maximum recording density of the printed matter is 1.8, after reaching 1.8, it becomes a straight line parallel to Dt (original density), so it is necessary to adjust both reflective and transmissive manuscripts in order to compress contrast and correct chromatic aberration to achieve suitable The range of printing and copying tone.
For example, the maximum density on a color positive document is Dt = 3.0, and the maximum recording density of printed matter is Dr = 1.8.
It can be seen from the curve that the reproduction of the printed matter cannot reach the highest density reduction of the original, because the materials used in the reproduction of the printed matter include ink, paper, photosensitive materials (film, PS-plate-), color sequence, and printing machinery. Limit, the maximum recording density Dr = 1.8, but when Dt = 3.0, the maximum density of the original is large, and only the contrast can be compressed, otherwise the actual effect will not be printed.
Prints often need to be adjusted when the tone is restored. When the density contrast of the original is greater than the highest recording density of the printed matter, in order for each tone of the original to be displayed on the printed matter, it is necessary to properly adjust the tone reduction. Secondly, in order to adapt to the copy requirements of some special manuscripts (such as photos with light tones and photos with dark tones), certain tones of the manuscript must be properly emphasized, and other tones must be compressed accordingly. The main feature of linear compression is the adjustment of equal proportions of each order. Linear compression does not represent true visual proportional compression, because the DY curve is also nonlinear. After this compression, the bright tone is in the human eye It is not easy to distinguish, resulting in "grey flat" phenomenon. [next]
Tonal duplication refers to the relationship between the density of the original and the percentage of dots copied.
To make all the tone and color on the manuscript can be well expressed on the printed matter, first select the correct gradation curve. Hierarchy is the basis of tone and color changes. If the layers on the screen are not rich, the expression of colors must be monotonous and tasteless. Only when the layers are realistic, can vivid color changes.
It is impossible to copy the originals faithfully, because the density contrast of most of the originals is greater than the density contrast of the printed products, so the copy must compress the density. Therefore, it is necessary to lose some of the subtle levels. In actual operation, the reasonable level curve should be adjusted according to the contrast of the original and the specific content of the tone, that is, the level of the secondary parts on the reflective or transmissive manuscript should be adjusted. Compression is carried out so that the levels of main parts are emphasized and characterized.
Under the premise of normal contrast of color manuscripts, adjust the gradation curve correctly according to different types of manuscripts. The level control of the Apple extension and color separation Apple computers is both convenient and flexible. It can be locally strengthened or compressed, but it is necessary to pay attention to the balance of the dichroic gradation curve. The neutral gray balance should be appropriate. The incorrect gradation curve will distort the replica. Therefore, we must pay special attention to the correct use of gradation when operating the electrical extension and Apple computers, but the color cast of the original can be corrected by adjusting the gradation curve.
When compressing the contrast of the original tone, the following methods are often used to compress some parts.
â‘ Normally, normal manuscripts have proper contrast and should compress the low-key levels more flat, especially when it is necessary to emphasize the middle and light tone levels.
â‘¡The original is too dull, and the bright tone is flat. If the dark tone and the middle tone level are emphasized, the middle tone level will be flattened accordingly.
â‘¢The contrast of the original is too dull. The whole painting-face-low-key-face-product-large, the low-key level should be pulled away, but the middle-tone level appears flat.
â‘£ The middle tone level of the original is relatively flat, and the contrast is small. The bright tone level can be compressed to make the contrast of the middle tone level larger.
⑤ The contrast of the original is basically suitable for printing and copying. The photos are mainly in the middle tone. The dark tone-area-product-is small, and the dark tone level can be compressed to emphasize the middle tone level.
â‘¥ Color photos are often encountered. These manuscripts are thin and have low contrast. For these manuscripts, the bright and dark tone levels can be compressed to make the contrast of the middle tone levels larger.
⑦The level of the bright tone level of the original is low, and the contrast is small. You can pull the bright tone level, but the middle tone level is flat. [next]
The contrast of the natural color positive film of the transmissive manuscript is relatively large, about 3.0. Normally, it is necessary to compress the contrast to meet the requirements of copying the printed matter; while the manuscript of the reflective manuscript has a small contrast and the manuscript is boring. Make a bright copy. For example, the main point of copying portraits is the skin color of the person, the two colors of y and m are the key points; the key point of copying the landscape picture is the natural scenery, and the two colors of y and c are the main points. Use the gradation travel button flexibly to adjust the reasonable gradation curve, correct the shortcomings of the original, keep the main part, and lose the secondary part accordingly, make bold choices, and try to achieve better results. However, if the adjustment of the gradation curve is unreasonable, it may cause the effect of the picture being reversed, the gradation is unclear, and the hue is inaccurate.
The color reproduction of printed matter mainly has the deficiency of basic colors. On the contrary, it has the disadvantage of excessive colors. To reproduce high-quality printed products, the basic colors should be deeper on the basis of not losing the level. The basic color should be 100%, the moderate basic color should be full, the light basic color should be appropriate, and the bright basic color cannot be lost.
The opposite color should be appropriate. Because the purity of the inks on the market is not bright enough, the hue and transparency are poor, and the whiteness and smoothness of the paper are poor, so when using the color, it is necessary to pay attention to the brighter complementary colors (opposite colors) to be smaller and denser. The complementary colors at the color should be used. The brightest small-surface-product color complementary colors can not be used, so they play the role of color change and set off the level. Properly applied can make the basic colors more vivid, thick and rich and realistic.
The color reproduction of the printed matter is actually an additive color reproduction of the three primary colors y, m, and c of the colorants, with the subtractive light as the primary color light. The three primary colors of y, m, and c are the basic primary colors of all colorful colors. The black-version--can't afford any color change, the black-version--is only to stabilize the gray balance, play a skeleton role in the color picture, make the dark tone darker, emphasize the low-key level and outline, enhance the picture The thickness and three-dimensional sense. The three primary colors of y, m, and c materials transition to the black field, that is, y + m + c = approximately black. A part of the background color (tri-primary color) of the neutral hair formed from the three primary colors of y, m and c is removed and replaced with black ink. This is the method of under-color removal (UCR) used by electrical extensions and Apple computers. There are many necessities for background color removal: â‘ improvement of printing suitability, generally used in dark tone areas, in dark tone areas, if printing with three primary colors, the dot-area-product- tend to be very high, when high-speed multi-color printing It is easy to cause problems such as over-thickness of ink layer and paste-version. If the background color is removed, it will greatly reduce the amount of ink, mainly save the amount of y, m, c color ink, improve printing suitability. â‘¡Conducive to control the neutral gray balance.
The length of the tone of the black version is determined by the amount of background color removal of the three colors y, m, and c. The amount of background color removal is large. The midtone and dark tone levels are flat. The black version is suitable for pulling the tone. Make it longer to compensate for the missing layers of the three-color version. If the three-color-version-removal volume is small, the black-version-tone can be shortened appropriately to avoid dullness in the middle tone. Dark tone is generally calibrated with the maximum density of the image to satisfy the image tone. It is necessary to calibrate according to the characteristics of the original, pay attention to the color balance of the dark tone, and at the same time, the dark tone calibration also needs to consider the relationship with the under color removal (UCR).
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