Application of the hottest Photoshop spot color ch

2022-08-14
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The role of Photoshop spot color channel in prepress inspection

the printing color of topographic map or thematic map is generally black, brown, blue, green or more spot colors, which is different from the general four-color printing of yellow, magenta, blue and black. Due to the particularity of its spot color, some common digital map publishing software first divides it into monochrome EPS or PS postscript files in general prepress processing

and plate splitting inspection is an important work before printing. The general inspection method is to proofread the monochrome sample of spray painting and division. The disadvantage of this method is that it can't check the nesting, the relationship between elements, capping, color proofing and so on. The root cause of this situation is that the layer of EPS vector file (or the layer when EPS is converted to gray-scale image) cannot be transparent and the gland is retained, which makes it difficult for color separation files to be combined to form correct color graphics, so it is difficult to realize color inkjet, and it is easy to make mistakes, so it is usually monochrome inkjet inspection

in my work, by using Photoshop spot color channel, the author converts monochrome EPS files of different color plates into gray-scale images, and then combines them into a color PSD file to implement color inkjet, realizing the effect of fast simulation printing color proofing (as shown in Figure 1)

I. convert EPS file to PNG gray image

1 Converting EPS (PS) to PNG gray-scale images through gsview

gsview is an English version of commercial software, which is mainly used to browse PS, EPS, EPI, PDF and other postscript language files, and can easily realize the conversion between these formats. The author uses gsview version 2.4. The following specific operations are briefly introduced below

(1) unit setting. In option/units, select the MM unit

(2) map height and width setting. Generally, the width of 1:50000 map can be set to 1600 × 1200, other size sheets can be set according to specific needs. In the menu "media/userdefined", enter the height and width value: 1600 × 1200。 The conversion formula of the exact value is: the required number = the actual size of the map sheet. The number of inches and millimeters of new composite materials under research ÷ 0.35278

(3) display definition setting. In the menu "me if you need to take the more complex parameter dia/displaysettings", the recommended values are as follows

① resolution:30dpi

② zoom resolution:300dpi

③ depth:default

④ textalpha:1

⑤ graphics:4

(4) print to file. After opening the file, select the menu "file/print/printsetup" and select pnggray under "device"; "Resolution" can be set to 500 (DPI); Select "print to file"; Print as a PNG grayscale file. The "resolution" value can be set as needed. Each sub version file only needs to be opened one by one and printed as a PNG file

2. EPS (PS) is converted into PNG gray images through acrobat distiller

acrobat professional's distiller module can convert EPS files into PDF files in batches, and then acrobat can open PDF files and save them as PNG files. The resolution can be set as needed during the conversion process

second, phototpe material is a kind of heat shrinkable elastomer with full closed cell structure. The customization of shop spot color channel and the input of spot color image are nested.

in Photoshop, you can create a new spot color channel and customize the ink color of the channel. We put the split monochrome files into different spot color channels to realize the superposition of channels. Because the channels are transparent, we can achieve the effect of color plate combination, and easily realize the operations of checking nesting, element correlation, gland inspection, etc. The simple operation process is as follows

1. Create a new file in Photoshop. The size is consistent with the PNG grayscale file generated in the previous gsview, and the resolution is consistent with that set in "resolution"

2. Establish spot color channel. Select "channel" in the window, click the small triangle in the upper right corner, and select "new spot color channel", you can establish each spot color channel and define its name, and adjust the ink characteristics of the channel (customize the CMYK content of its ink) according to the color of the divided EPS, so as to achieve the effect of simulated printing. For easy identification, the channel name can be defined as the name of the plate color. The channel sequence is in the order of each edition of the publishing gland (as shown in Figure 2)

3. Copy the monochrome partition PNG file to the spot color channel. Open the monochrome PNG file, select all, copy and paste (or drag) the content into the corresponding spot color channel established in the previous operation. You will see that the data has been displayed according to the color setting of the channel, and the effects of capping and overprint simulate the printing results

if a large number of map sheets are checked, the established spot color channel can be saved as a template, and the nesting process of each version can be saved as the action of Photoshop, so that the saved action can be used in the later nesting, which is very convenient to realize nesting and improve efficiency

III. prepress inspection

digital proofing output inspection or screen inspection can be used

using a drawing printer to directly spray a paper map can greatly improve the work efficiency. It is convenient to check the content of the sub version, and it is also convenient to draw errors on the paper map

when there are few errors, you can directly check the screen and modify the data directly if you find errors. If you want to mark errors, you can continue to apply the channel principle, and establish a channel with eye-catching color on the top layer (this color should be significantly different from the colors of each version in the figure), which can generally be red. With Photoshop tools, you can easily plot errors and add text notes on this channel

IV. conclusion

this method has been widely used in the actual work of our unit, which conveniently realizes the rapid realization of the color digital proofing of the divided version EPS, thus providing a strong technical guarantee for the review and acceptance work, saving a lot of inspection time, improving the work efficiency and map quality, and eliminating many previously difficult to find errors such as capping and overprinting. Its main advantages are as follows

1. Simulated printing proofing and realized digital proofing

we use a microcomputer with a spray printer, and the process completely simulates the effect of Laser Phototypesetting of monochrome EPS files. After printing with film, we use various inks

2. It saves time and improves efficiency

the method of converting EPS into PNG images used in this process is basically the fastest and most effective method among various methods, which is more than 10 times faster than the direct conversion using Photoshop; The PNG format selected as the image format is more than 5 times smaller than the JPEG file with the same content in most cases

3. The error that cannot be found by monochrome inspection before is avoided

this process avoids the consequences of white area error capping formed by merging various versions of EPS files in vector software such as illustrator, but converts EPS into gray-scale images and puts them into the channel, which completely simulates the effect of ink distribution in printing, thus providing convenience for image search and avoiding errors such as capping and overprinting that could not be found in previous monochrome inspection

in addition to map prepress inspection, other similar sub edition EPS (PS) documents can use this process for reference to implement prepress inspection, but for different color designs, we need to customize different spot color channels

source: keyin

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