If you are one of the millions of people that think converting to CMYK simply means going to Image / Mode / CMYK and viola you have a CMYK image ready for press, you may want to think again. The reality is that there are numerous flavours of CMYK, from Web to Sheetfed and coated to uncoated. Simply choosing the default may not be your best choice. The goal is to target your image using the correct flavour of CMYK. But what are the specific printing conditions or flavours? Lets break them down.
SWOP, Web Press
Everyone has heard of SWOP (Specifications for Web Offset Publications) but not everyone knows what SWOP means as it pertains to their image and its reproduction. The original US Web Coated (SWOP) v2 profile has been around for a while but is slowly being replaced by the more accurate and up to date WebCoatedSWOP2006Grade3.icc and WebCoatedSWOP 2006Grade5.icc profiles. They are installed with CS4 and CS5.
One of the main differences between SWOP and a Sheetfed press is the amount of ink viscosity or thickness. The US Web Coated (SWOP) v2 profile puts down an ink volume close to 300% total area coverage in the darkest tones compared to 340-350 for sheetfed.
But what else makes a Web press unique? Web presses are faster, up to 40,000 impressions per hour and are designed for longer run lengths (20,000 impressions). Limitations of a Web or roll fed press are stock choices and paper thickness. Gamut; a web press printing on a number three stock has a smaller gamut compared to GRACoL on a number one stock.
GRACoL is defined as General Requirements for Applications in Commercial Offset Lithography or printing on a number 1 sheet on a sheetfed press. GRACoL is gaining in popularity and has proven to be an excellent specification for colour reproduction in the sheetfed arena.
Remember our discussion on ink thickness; the GRACoL spec for TOC is 340% verses 300% for Web. This is a notable difference because a large majority of images are converted using the US Web Coated (SWOP) v2 profile and it has a TOC that is too low for a sheetfed press. The result is the photograph prints lighter than expected in the shadow regions because the sheetfed press is starved for ink.
So what can you do to ensure your images are given their full potential? Here are a few rules. If you are unsure use the default US Web Coated (SWOP) v2 profile. It is better to have too little ink than too much. But if you can determine that your job is going to be printed on a quality stock with a sheetfed press then use the GRACoL2006_Coated1v2.icc. Always use Photoshop’s convert to profile option and select the options seen in the screen capture below.
I used the default CMYK settings in Photoshop and get good results.
I call this a blind conversion because you have no idea what flavour or recipe of CMYK you are using. Don’t do it!!! Use the Convert to Profile option and select your flavour of CMYK.
Converting from CMYK to CMYK in the convert to profile is destructive? No.
This is not a damaging conversion if done once. Sure if you do it 15 times it will degrade the image but not once. But the benefit is that you can repurpose a CMYK to another printing conditions using this method.
Traditional Separation Tables are more accurate than ICC profiles for making Colour separations/conversions? Big fallacy here, traditional separation tables are significantly less accurate then today’s ICC profiles supplied in Photoshop.
I can’t specify dot gain when using an ICC profile so I prefer to use Separation Tables where I can dial in the parameters. The dot gain values are built into the ICC profile as well as the white of the paper and the Total Ink Limit.
Understanding the differences will help you make a more informed decision when converting your images for print and always ask your CSR or print broker how the job is being printed and convert your images accordingly.