The DCS file format
DCS stands for Desktop Color Separation. It is a file format that is based on the EPS file format. In fact, you could regard DCS files as a collection of EPS files.
DCS files are mainly used to exchange bitmap images between prepress applications. Occasionally DCS files are also used for vector data or text. The main advantage of DCS over its parent EPS file format is that it adds a kind of OPI-functionality to the file format. Since DCS files contain separate EPS-files for each plate, an application can generate and print colour separations faster when the DCS format is used. This was a valid approach when when Macs, PCs and software were not as powerful as they are today and when all output was done from the lay-out application. In today’s world with the increased popularity of in-rip separations as well as improved support of EPS-files within applications like QuarkXPress, DCS can be a very inefficient file format.
As already noted, DCS-files are actually EPS-files that have to follow the Adobe specifications (Appendices G and H of the PostScript Language Reference Manual, 2nd ed.). The only differences are some changes in the header comment area as well as additional comment lines in the main section of the file that describe the separation data. DCS-files contain a preview image, just like EPS-files.
There are two different versions of the DCS file format: version 1 and the more recent version 2.0. Both formats are covered in more detail below.
DCS 1.0
DCS 1 was developed by Quark to add a file format that could easily and efficiently be separated to their main application, QuarkXPress. This file format is usually referred to as DCS.
A DCS 1 file is composed of 5 separate files. Below you see such a file: the main file has the extension .eps while the 4 other files have an extension that marks the color data they contain. The file size shows that the main file does not contain any actual image data but only a preview image and pointers to the other 4 corresponding highres files.
Because the main file has lines in it that refer to the other files, you cannot simply rename DCS-files in the Macintosh Finder or Windows Explorer. If you want to change the name of a DCS-file, it is best to open it in Photoshop and use a SAVE AS to save the file using a different name.
The image data in the four CMYK-files can be compressed using JPEG compression. This has often posed problems with OPI-systems and older RIPs sometimes also choke on the decompression.
DCS 2.0
Development on the DCS-2 format started in 1993 and it became available in 1995 or so. These are 2 new features in DCS 2.0:
- The option to choose a multiple- or single-file version. DCS originally required that the separation files be separate. With DCS 2.0, these files may now be combined into one. Please note that this does not turn DCS-2 files into true composite files, just look at single file DCS-2 files as a collection of separate files that are glued together to form one big file.
- The ability to specify additional plate colors. DCS 2.0 can point to spot color plates in addition to the standard cyan, magenta, yellow, and black. This ability makes DCS-2 the ideal file format for hexachrome images. These contain 6 colors: cyan, magenta, yellow and black as well as orange and green.
Early design applications did not support DCS-2 files. This includes versions of QuarkXPress prior to 3.32 and PageMaker 6.5. Because DCS-files are a kind of EPS-files, they can be imported in these applications but the output on film or plate is incorrect.
DCS must die
DCS made a lot of sense 10 years ago but in todays world it has become a real nuisance. The main problem is that popular applications like QuarkXPress and InDesign (before the CS release if I am correct) do not properly support DCS-files when they print composite PostScript files (files that are not yet separated, with the separation option switched ‘off’ in the PRINT-menu). Instead of reading the high-res data in the DCS-file, they only include the lowres screen preview in their composite printfiles. If you fail to notice this, the output will contain ugly 72-dpi images. Some more recent lay-out applications can merge DCS-data when generating their output file.
Although there are extensions on the market to solve this problem (SmartXT for XPress) and most OPI-servers can merge the highres data when OPI is used, DCS is simply a nuisance and deserves to disappear, at least for pure CMYK images.
If you need more than 4 colors in an image (e.g. hexachrome) or you wish to process copydot files, then DCS is still a valid file format. Using native Photoshop files is probably a better alternative if your design program supports this. For simple CMYK images DCS should never be used anymore.
Specsheet
Name: EPS DCS
Developer: Quark
Release date: ?
Type of data: bitmap
Number of colors: ?
Color spaces in practice: DCS-1: CMYK or 1-bit copydot, DCS-2: CMYK, hexachrome or copydot
Compression algorithms: JPEG
Ideal use: exchange of images between prepress applications
Extension on PC-platform: .DCS, .C, .M, .Y and .K for the separate colour files.
Macintosh file type: ?
Special features: can be troublesome in composite workflows
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DCS renders a smaller file for some reason reducing bandwidth. I have found that DCS 2.0 files are smaller than regular EPS – maybe the size of the preview differs? I notice this difference in filesize between .psd and .eps has not been discussed in your article. I think an explanation would add greatly to your informative discussion of DCS.
Best, Tim
If you knew anything about print and how a press operates then you would understand the importance of a DCS file. The fact that when printed on a small digital print machine it prints lo-res matters not. The DCS conversion tells you that the composite will be 72 dpi… So don’t use it. Make a CMYK version of the file you wish to proof. Also make a proof layer for it (for hi res printing purposes) and also create at the same time a DCS layer for the pre-press operators to use in separation.
The DCS file should only be used for a six color separation (Hexachrome) and that’s it… period. This really helps when you are printing on strange surfaces or your vector based graphics cannot create the proper effect you want but you still want to preserve the PMS color you are using. (i.e. Using graphics with any sort of transparency. Most vector graphics programs will warn that it may cause problems using transparency when separating the file.) And yes you can print straight from vector programs but be warned if you use any gradation or special feather affects it may print warped on a press.
So that is the purpose of the DCS file. And most designs, at least print wise, are not simple CMYK files. If you want your design to print right PMS colors are the way to go. Ask any major pre-press or flight-check operator or printer. Yes there are new ways to separate colors and new digital presses that go straight to plate but not many companies out there can afford a machine like that. Plus most companies for ‘HIgh Quantity Output’ won’t use a digital press. While they may be faster than digital copiers and machines. They are slow and in-efficient in higher quantities and are better used for short-run printing. Don’t knock the DCS file until they come up with a better way to separate PMS colors in vector based programs.
Thanks for the concise and straight-forward inf
Alf
DCS files are a pain in the rear for prepress operators. It basically means that the designer didn’t trust the prepress operators. Just use the vector program – Illustrator and Photoshop are smart enough. Apparently DCS users have underlying trust issues. The author was right. DCS must die. Both Corel and Adobe have WORKED AROUND this old, antiquated format.
But does anyone know how to open and save a DCS2 file when one is given to you?
I have 3 that I need to save as a flattened hi-res file. It is 2400dpi right now, but I don’t have any experience using this format.
Can it be done with Photoshop CS or Illustrator CS. I can’t find any ‘how to’ directions anywhere.
thank you.
Mike
It depends on the source application whether you can open such a file in Photoshop CS. If it is a pure DCS-2 color image, Photoshop should be capable of opening it. If it is a copydot scan (which your reference to ‘2400 dpi’ seems to refer to), Photoshop might not be capable of coping with the data. Just give it a try.
Hi Laurens,
thanks for writing back. I didn’t think anyone was going to write back.
Well, I have tried opening it in Photoshop CS and it opens blank, but if I do a ‘browse’ to look at thumbnails I can totally see the image. I am clueless on why it doesn’t show in Photoshop. What about Illustrator CS? It says “DCS EPS files cannot be opened or embedded. Please PLACE this file using the LINK option.” How do you do this? I am totally clueless.
Thanks again for the help.
You don’t specify whether it is a single or multi-file DCS-2 file. If it is a multi-file DCS-file, you could try opening each separate high-res channel in Photoshop to manually merge them into a single file.
Another solution might be to place the DCS file in InDesign. I think all versions since CS or so are capable of merging the highres DCS data back into a composite file. That means you could export a highres PDF out of InDesign or have a go at any of the other file formats that InDesign supports.