Prepress graphic processing question and answer

Why can black version have different types?
A: There are different types of black settings for different color separations: None, Light, Medium, Heavy, Maxium, etc. It means that the color of the black and gray places on the image can be divided into the black version, the light black version, the black version, the heavy black version, and the full black version when separating colors. So why black or gray can be divided into different sizes of black version of the dot?

We know that the pure black version can represent the gray series colors, and the yellow, magenta, and blue primary colors can also express the gray series colors, and the yellow, magenta, cyan, and black colors can also express the gray series colors.

If it is completely represented by yellow, magenta, and blue neutral gray colors, then the black version of the Internet point is 0%, where the black version is None;

If the neutral gray color is represented by a pure black version, it is a Maxium type black version;

If neutral colors are represented by yellow, magenta, cyan, and black colors, the Internet version of the black version is larger, and the dots of yellow, magenta, and cyan are smaller. When the Internet version of the black version is relatively small, the dots of yellow, magenta, and blue are relatively large, forming a relationship between the two sides, and then there will be a black version of Light, Medium, Heavy and other types. Such as color R163G163B163, can be divided according to the following situations:

When the black version is Light, the color separation result is C40%M33%Y33%K1%; when the black edition is Medium, the color separation result is C37%M30%Y30%K7%; when the black version is Heavy, the color separation result is C26. %M20%Y20%K22%;

It can be seen that there is still a big difference between their color separation results, but the printing results should be similar.

The above discussion is about color separation results for neutral gray color. In fact, the black version type will have different effects on the complex color in the image. Because the complex color contains a gray component, there is also a gray component and how to assign yellow. Problems with the proportion of magenta, cyan and black editions. Such as brown red R186G139B10, the separation results are:

When the black type is Light, C33%M39%Y100%K13%; when the black type is Medium, C26%M31%Y99%K23%; when the black type is Heavy, C70%M24%Y99%K32%.

What is a Separation Table? What does it do?

A: The color separation table is actually the sum of the various settings when separating colors. Figure 1, it includes Ink color, Dot Gain, Separation Type, Black Generation, Black Ink Limit, Total Total Ink Limit and other parameters are set. This is a feature of flexibility and pertinence in Photoshop color separation. It works when the RGB color mode is converted to CMYK mode, that is, color separation, and their different settings will produce different color separation effects. After Photoshop 5.0, color separation tables have been made under the color management settings of the CMYK color mode as part of color management.

What does the ink color setting mean? Why ink color settings?

A: There are many ink types in the ink color type drop-down menu (actually options printed on different substrates). See Ink Color in Figure 1. This actually includes two aspects, namely, the type of ink used in the selection of printing, and the type of printing paper to be selected. Here Toyo Inks refers to Japan's Toyo Ink; Eurostandard refers to European standard ink colors; SWOP refers to web offset standard ink colors; Tektronix phaser III Pxl refers to Tektronix printer ink colors. Coated refers to coated paper (such as coated paper), Uncoated refers to non-coated paper (offset paper), and Newsprint refers to newsprint. Therefore, the Ink Color option actually selects the color that you use when printing your ink on the substrate you are using. Because China's domestic ink has no corresponding option in the menu here, in actual operation, such as printing on coated paper, it is recommended that you use Toyo (Coated) or SWOP (Coated); If you print on offset paper, you can choose Toyo (Uncoated ) or SWOP (Uncoated).

So why do you want to set ink? This is because there are different choices. The result of color separation will also be different. That is, the ink you choose is similar to the ink you use to ensure that the color can be accurately restored during printing. In addition, since the same ink can have different colors on different papers, the ink color on the same paper as you printed can be selected to ensure correct separation results.

How large is the Dot Gain at the color separation table?

A: Dot enlargement is the phenomenon of dot gain caused by the printing pressure and the diffusion of ink on the substrate during the printing process. This phenomenon is proven to exist. The size of the dot expansion value is affected by factors such as printing pressure, substrate, and ink viscosity; the larger the general printing pressure is, the larger the dot expansion is; the stronger the absorption of the substrate is, the larger the dot expansion value is. Specifically, newsprint paper, offset paper, and coated paper have the largest value of newsprint paper, and coated paper is the smallest. For different sizes of outlets, the dot expansion values ​​are not the same. Generally, the high-profile and dark-spot network expansion values ​​are small, and the median tone network expansion value is large.

The Dot Gain is set in the color separation table in order to pre-compensate the phenomenon of dot gain during printing. That is, the dots are appropriately reduced when the color is separated, and the desired size is obtained after the dots are expanded during printing.

So how large is the setting of outlets? The simple method is mainly to set the maximum value of dot gain, and Photoshop will compensate the dot of each tone based on this value. If it is set according to the curve, it can measure the enlargement value of each order in the actual printing conditions, and generate a curve, and compensate the expansion of the dot by the curve. This compensation is more accurate. In practice, it is difficult to determine the dot gain value. In general, it is recommended to use Photoshop's Dot Gain default setting. For example, the default value is about 17% when printing on coated paper, about 22% when printing offset paper, and about 30% when newsprint is printed.

When to choose GCR when color separation? Under what circumstances choose UCR? What is the difference between GCR and UCR separation results?

With GCR, it is easy to maintain the gray balance, reduce the total amount of ink overprinting during printing, make the ink dry faster, and increase the printing speed. For general images, color separation in Photoshop generally chooses GCR. UCR means the removal of the background color. The main object of the UCR is the darker complex color in the image, and the gray component of the color is replaced by the black K. However, the scope of UCR is smaller than that of GCR. The GCR has a wide range of effects, generally starting from a range of 20% of the grayscale ruler, whereas UCR generally only acts on the darker tone. Therefore, UCR can be used for color separation in images with high color and dark tone.

The difference between the two is that the level of the black version of the GCR separation is more and the tone is longer; while the level of the black version of the UCR separation is less, but in the deepest place, the value of K is larger.

What does Gray Ramp mean?

Answer: The curve in the figure actually represents the separation result of neutral gray, it can also be said to be a color separation curve, or it can be said as a gray balance curve. The result of the neutral ash separation at point A in Figure 2 is called C50%M40%Y38%K12%.

What does Black Ink Lmit (black ink limit or black ink maximum) mean? what's the effect?

A: The maximum value of the black ink is the maximum percentage of the Internet version of the generated black version when the color is separated. It can control the size of the dots in the black version of the separation, so that the color is not too dark when separating colors. At this time, the size of the input value has a definite effect. If a color is 100% at Black Ink Lmit, the result is C80%M69%Y63%K68%, while the result at 70% for Black Ink Lmit is C89%M29%Y83%K51%. As can be seen from the data, the size of this value will directly affect the color separation result, but the color will not be greatly changed. As shown in Figure 3, it can be clearly seen from the color separation graph that the Black Ink Lmit is 100% and 70% difference, respectively.

What does Total Ink Lmit mean?

A: Here Total Ink Lmit refers to the maximum ink overprint amount for four-color printing, that is, the four-color field Y, M, C, K (net 100%) in the overprint, how much the actual overprint. Because if the ink is completely overprinted in the ink layer of the first printing ink, the overprinting rate will not be 100%, generally less than 100%, so the total overprinting of the four-color field overprinting is between 320% and 360%. Therefore, it is recommended in Photoshop that Total Ink Lmit is generally set to be between 320% and 360%. The dichroic curves at settings of 320% and 400% are shown in Fig. 4. The color separation results of the same color R59G66B43 are: when the total ink volume is 320%, C67%M48%Y81%K56%; when the total ink volume is 400%, C67%M48%Y81%K56%.

What does CMYK Setup mean after Photoshop 5.0? CMYK model generally choose what is better?

A: Before Photoshop 4.0, there was an option specifically for setting the Separation Table, which can be opened under the File\Color Settings. After Photoshop 5.0 changed to File\Color Setting\CMYK Setup. It is recommended to use the Built In button here. Because flexible settings can be used at this time, the separation conditions can be the same as the actual printing conditions. All the settings below the built-in are similar to the two previous versions of Photoshop 4.0, Separation Table and Printing Inks Setup.

A scanned RGB mode has black text on color originals. If you want to use the scanned words directly, what color is best for these words? How to achieve this ideal requirement?

A: For the black text and lines on the color image of RGB mode, it is best to process only the dots on the black version to form monochromatic text when color separation and adjustment, so that the color value of the word is C0%M0%Y0%K100. %. Because, if it is composed of four colors C, M, Y, K black text, if there is a bit misplaced at the time of overprinting, there will be ghosting or colored edges.

There is an easy way to achieve your goal: to select the black version as Maximum in the separation settings. At this time, all the grays of the black or the complex color are separated into only dots on the black version, which can be achieved when RGB→CMYK is performed. If a black R15G14B14 color separation into C0%M0%Y0%K95%, and if the color separation setting, the black version is Light, the color separation result is C79%M78%Y73%K76%.

When is it better to convert the image from RGB mode to CMYK mode?

Answer: Since the storage space and memory occupied by the RGB image is small, the processing speed is faster when adjusting, so the emphasis on image sharpness and noise removal processing are better under RGB mode. Therefore, it is recommended that when the image is adjusted, the image must be cleaned and the resolution must be corrected before changing to CMYK. Then proceed with color processing. Because even if the color is processed in the RGB mode, after changing to CMYK, the color will still change.