CMYK Ink, SWOP, Sheetfed, WebPress. If you are a designer scratching your head, you probably need to read this!
CMYK Ink, SWOP, Sheetfed and WebPress. Whew! You are likely a graphic designer, a book designer, or simply a DYI self-publisher trying to make your files ready to print on press. You’ll need to understand these terms to make sure that your files are set-up properly in InDesign, and that images convert correctly in Photoshop.
This article began as a question from a graphic designer who is setting up a book that we are printing. Since there’s some confusion over terms and when to use certain settings, we thought that other designers of print materials would find explanations helpful. Understand the difference between a sheetfed press and webpress. She also had questions about CMYK ink and black and white images. After all, you want the best book possible, and that is what we provide at Star Print Brokers.
SWOP and US Sheetfed Coated v2
Q. I have some questions specifically regarding the CMYK ink conversion for sheetfed press. Our images are currently in SWOP v2, and from reading your website, we need to convert to US Sheetfed Coated v2. From doing a bit of research, SWOP puts down less ink and will print lighter if unchanged. What about that?
A. SWOP is the default setting in InDesign. To fine tune the images for optimal success, you need to convert color images in Photoshop to US Sheetfed Coated v2. Black and white images do not be converted.
There are other processes at work in prepress that designers don’t need to worry about, but about less ink … When the 4 inks are laid down in process color printing, there would be a buildup of ink unless we removed some of the ink. Decades ago, a standard practice was Gray Color Replacement and / or Under Color Removal, or GCR or UCR. Now, GCR happens anyway, when you convert from CMYK ink to RGB.
UCR is a process the printing facility would calculate. This is all done automatically and should never be a concern to the designer. There are a number of things done automatically. Gone are the days of the designer ‘trapping’ files too.
Batch converting from SWOP (for webpress, roll stock) to Sheetfed (printing on sheets)
Q. I am considering batch processing the conversion from SWOP to Sheetfed and adjusting our color swatches to match the new CMYK ink screen builds. Your guidance?
A. While you can do a batch process on the conversion, watch that color doesn’t shift. It shouldn’t, as the images should already be in CMYK, not RGB. However, if converting from RGB, you will see a shift in color some of the time, but not on all images. The shift mostly happens in blues, fuchsia, and metallic colors. I like to point these out to photographers, so they are made aware of any shift in CMYK ink color. Watch those blue skies!
The color shift holds true for Solid Spot inks converting to Process color, CMYK ink. If the inks in your swatch palette are already in Process, you should not see a color shift. The color shift is just a fact of printing on any press, SWOP or US Sheetfed profile, anywhere, with any printer. There is no way around it, unless we put a monitor on every page of the book! The color for children’s books is important too.
Adding Warm or Cool Tones to Black & White Images
Q. Some folks suggest doing a subtle cool or warm tint for black and white images, to control any color shift that may occur on press. Do you have any guidance on converting black and whites?
A. Since true black and white images only use only black ink, there should be no CMYK ink color shift. Be careful though — if you have a solid black or very dark background behind the image — one that is built out of process color, or a spot ink other than 100 percent black.
We try to caution folks about printing black ink backgrounds, as there is sometimes a certain amount of ink pick-up that affects the images. Most of the time, the average person doesn’t see it. But, when working with professional designers and photographers — we like to point out what can happen — so that they know what to expect. This is a situation where GCR cannot balance the effects of such heavy ink.
Use Warm or Cool Black and White to Tone Process Color Images
You can indeed print a process color image as a virtually black and white image, by adjusting the CMYK ink values in Photoshop. If you want to apply a warm or cool tone to all black and white images, it would be easier to adjust them as process color images.
Use of Duotones
You can also print the images as duotones. See the article on duotones for instructions. The problem with adding one or more duotones is that it changes the quote, and costs more for printing. It is because you are adding new ink(s) to the set-up. So, with one duotone, a 4 color process book becomes a 5 color job; process color plus the 1 spot ink used as the consistent background color in the duotone.
If you had a warm tone and a cool tone, that would be two additional inks and again, increases the cost to print. You could also forego using process color, and for the same cost as process, add 4 specific inks to 4 different duotone possibilities.
In conclusion, my suggestion for this book is to either convert all the black and white images to process color, adjusting each for a cool or warm tone, or have all black and white images converted to 100 percent black grayscale. In Photoshop, go to Image > Mode > Grayscale.
Review of Terms: CMYK Ink, SWOP, Sheetfed, WebPress
CMYK – The 4 inks used in process color printing: Cyan, Magenta, Yellow and blacK.
SWOP – Specifications for Web Offset Publications (webpress).
Sheetfed – Any press that prints on sheets of stock / paper. The sheets are printed one at a time. In the case of books, we print on sheetfed presses, and the sheet is large. The press usually prints 8, 12, 16, or 32 pages on the front and back of the sheet. They then fold into signatures, like a booklet. The signatures are then assembled into the book block. They are then Smyth sewn or glued together, and placed into the cover or hard case.
WebPress – A press that prints from large rolls of paper stock. Newspapers always print on a this type of press. Depending on the quantity, direct mail, sell sheets, or flyers are often printed on a webpress. The printing is just not as accurate on a webpress than on a sheetfed press, particularly process color CMYK ink. This is why we print all our books on sheetfed, not web.
Commercial printers often have both webpress and sheetfed presses. Presses can be 1 color, 2, color, or 4 color process CMYK ink. More often, printers have at least one 6 color sheetfed press.
Note: While the terms and settings we note here, are applicable for books as well as other documents; check with your printer. This post is written with the assumption that you are printing books with Star Print Brokers. Also, check our prepress guide.