Computer graphic design and prepress graphic processing Q & A
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Why can the black version have different types?
A: The black version will have different types due to different color separation settings: None, Light, Medium, heavy, Maxium, etc. It means that the color of the black and gray places on the image can be divided into no black version, light black version, medium black version, heavy black version, all black version, etc. in the color separation. So why can black or gray be divided into black-sized outlets of different sizes?
We know that the pure black version can represent the gray series color, and the yellow, magenta, and cyan primary colors can also represent the gray series color. The yellow, magenta, cyan, and black colors can also represent the color of the gray series.
If the neutral gray color is completely represented by yellow, magenta, and blue, then the black version of the Internet access 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 the neutral color is represented by four colors of yellow, magenta, cyan, and black, the black dot is larger, and the yellow, magenta, and cyan dots are smaller. When the black version of the Internet access point is small, the yellow, magenta, and blue dots are larger, forming a relationship of long-term elimination, and then there will be a black version of Light, Medium, Heavy, and the like. For example, the color R163G163B163 can be separated according to the following conditions:
When the black version is Light, the color separation result is C40%M33%Y33%K1%; when the black version 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 the results of their separation, but the printing results should be similar.
The above talks about the color separation results for neutral gray color. In fact, the black version type also has different effects on the complex color in the image, because the complex color contains gray components, and the gray component also has how to distribute yellow. The problem of the proportion of magenta, cyan and black. Such as brown red R186G139B10, the color separation results are:
When the black version type is Light, C33%M39%Y100%K13%; when the black version type is Medium, C26%M31%Y99%K23%; when the black version 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 color separation. As shown in Figure 1, it includes Ink color, Dot Gain, Separation Type, Black Generation, Black Ink Limit, and total The setting of parameters such as Total Ink Limit. This is a feature of Photoshop's flexibility and pertinence when it comes to color separation. It works when 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, the color separation table has been made under the color management settings of the CMYK color mode, becoming part of color management.
What does the ink color setting mean? Why do you want to set the ink color?
A: There are many ink types in the Ink Color Type Settings drop-down menu (actually the option to print on different substrates). See Ink Color in Figure 1. This actually includes two aspects, namely, the type of ink used in printing, and the type of printing paper. Here Toyo Inks refers to Japan Toyo Ink; Eurostandard refers to European standard ink color; SWOP refers to web offset standard ink color; Tektronix phaser III Pxl refers to Tektronix printer ink color. 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 is actually to choose the color of the ink you use when printing on the substrate you are using. Because China's domestic ink does not have the corresponding options in the menu here, in actual operation, such as printing on coated paper, it is recommended to use Toyo (Coated) or SWOP (Coated); if printing on offset paper, you can choose Toyo (Uncoated ) or SWOP (Uncoated).
So why do you want to set up the ink? This is because the choices here are different, the results of the color separation will 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 will be printed on different papers, there will be differences, so choose the ink color on the same paper as you did to ensure the correct color separation results.
What is the appropriate setting for Dot Gain at the color separation table?
Answer: The dot enlargement is a phenomenon in which the dot is enlarged due to the printing pressure and the penetration and diffusion of the ink on the substrate during the printing process. This phenomenon is proven to exist. The size of the dot gain value is affected by factors such as printing pressure, substrate, and ink viscosity; the larger the printing pressure, the larger the dot gain; the stronger the substrate absorbency, the larger the dot gain value. Specifically, newsprint, offset paper, and coated paper have the largest dot-width expansion newsprint and the smallest coated paper. For different sizes of outlets, the dot gain value is not the same. Generally, the high-profile and dark-adjusted dot gain values are small, and the mid-tone dot gain value is large.
Dot Gain is set in the color separation table to pre-compensate the phenomenon of dot enlargement in printing. That is, when the color separation is performed, the dot is appropriately reduced, and when the dot is enlarged at the time of printing, the desired size is obtained.
So how big is the dot size increase? The simple method is mainly to set the maximum value of the dot gain, and Photoshop will compensate the mesh points of each tone according to this value. If it is set according to the curve, the expansion value of each tone point under the actual printing condition can be measured, and a curve is generated, and the dot expansion is compensated according to the curve. This compensation is more accurate. It is still difficult to determine the dot gain value in actual work. In general, it is recommended to use Photoshop's Dot Gain default setting. For example, when printing on coated paper, the default value is about 17%, the default value for offset paper printing is about 22%, and the default value for newsprint printing is about 30%.
When do you choose GCR for color separation? When do you choose UCR? What is the difference between GCR and UCR color separation results?
The GCR is easy to maintain the gray balance, reducing the total amount of ink overprinting during printing, making the ink dry faster and increasing the printing speed. For general images, GCR is generally selected for color separation in Photoshop. UCR means the removal of the underlying color. The object of the UCR is mainly for the darker black complex color in the image, and the black component of the color is replaced by black K. However, the scope of UCR is smaller than GCR. GCR has a wide range of effects, generally starting from the gray scale of 20%, and UCR is generally only for dark adjustment. Therefore, for high-definition images with more color and richer darkness, UCR can be selected for color separation.
The difference between the two is: the black version of the GCR color separation is more, the tone is longer; the black version of the UCR color separation is less, but in the deepest place, the K value is larger.
What does Gray Ramp mean?
A: The curve in the figure actually shows the color separation result for neutral gray. It can also be said to be a color separation curve, or a gray balance curve. The result of the neutral ash coloration as shown in point A of Figure 2 is called C50% M40% Y38% K12%.
What does Black Ink Lmit mean for black ink limit or black ink maximum? what's the effect?
A: The maximum value of black ink refers to the maximum percentage of black dot internet points generated when color separation. It can control the dot size of the black version when color separation, so that the color is not dimmed when color separation. 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%, and a result of 70% at Black Ink Lmit is C89%M29%Y83%K51%. As can be seen from the data, the size of this value directly affects the color separation results, but the color does not change much. As shown in Figure 3, it can be clearly seen from the color separation graph that Black Ink Lmit is 100% and 70% difference, respectively.
What does Total Ink Lmit mean?
A: Total Ink Lmit here refers to the maximum amount of ink overprint in four-color printing, that is, the four-color field of Y, M, C, and K (100% of the dot), the actual overprinting amount when overprinting. Because the ink is completely overprinted on the ink layer of the first printing color, the overprinting rate is not 100%, generally less than 100%, so the total amount of overprinting in the four-color solid overprinting is between 320% and 360%. Therefore, it is recommended in Photoshop that Total Ink Lmit is generally set between 320% and 360%. The color separation curves at the set values of 320% and 400% are shown in Figure 4. The color separation results of the same color R59G66B43 are: C67% M48% Y81% K56% when the total ink amount is 320%; C67% M48% Y81% K56% when the total ink amount is 400%.
What does CMYK Setup in Photoshop 5.0 and later refer to? What is better for the CMYK model?
A: Prior to Photoshop 4.0, there was an option for the Separation Table setting, which can be opened under File\Color Settings. Photoshop 5.0 will be changed to File\Color Setting\CMYK Setup. It is recommended to use the Built In button. Since the flexible setting can be used at this time, the color separation conditions and the actual printing conditions can be made the same. All of the settings below are similar to the Separation Table and Printing Inks Setup versions of Photoshop 4.0.
Scanned RGB mode color originals have black text. 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 the color separation and adjustment into only the black dot with dots, forming a monochrome text, so that the color value of the word is C0%M0%Y0%K100 %. Because, if the black text is composed of four colors C, M, Y, and K, if there is a slight misalignment during overprinting, ghosting or colored edges will appear.
There is an easy way to get the most out of your goal: to choose the type of black version as Maximum in the color separation settings. At this time, all the black or multi-color parts of the gray color are separated into only the black version with dots, which can be realized when RGB→CMYK is executed. For example, a black R15G14B14 is separated into C0%M0%Y0%K95%, and if the color separation setting is made, the black version is Light, and 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 RGB images are small, the processing speed is faster when adjusting, so the image sharpness emphasis and denoising processing are better in RGB mode. Therefore, it is recommended to first clean the image when the image is adjusted. After the resolution is processed, turn it to CMYK. Then proceed to color processing. Because even if the color is processed in RGB mode, the color will change somewhat after switching to CMYK.