COLOR PRINTING 101
What Do I Need to Know?
Printing has changed a lot in the past 10 years. Advances in the desktop applications have made life much easier for those designing print projects and the print shops that run the jobs. Specifically PDF files have evolved into a robust way to view and troubleshoot jobs before expensive plates or film is made, saving time and money. Prior to PDF's, graphic designers and printers had to wait nervously for proofs to be pulled to tell if everything was working right. Now you can quickly generate a PDFX-1A file directly from the Adobe applications and see how the file is separating into printable layers. Despite this fact - the fundamentals of how files are built (CMYK vs RGB) and the limitations of vector vs bitmap images - none of this has really changed. What follows are a few topics we think are helpful when designing for print.
Color Models and Color Spaces
Lab/RGB/CMYK are all computer formats that can describe color. They are “color spaces” meaning that they are specific ways of defining color in a digital format. LAB was developed in 1931 by the International Commission on Illumination and was further refined in 1976. This is an international standard and many graphic & image editing programs use this file format internally even though the final export format might be RGB or CMYK. Photoshop for example uses LAB when calculating color space conversions.
RGB is a color model that deals with projected images such as computer monitors, TV’s and digital projectors. This is an “additive” color space meaning that adding Red+Green+Blue light together produces White.
CMYK in contrast to RGB, is a “subtractive” color space to describe reflected color. Examples of this are offset printing, ink jet (Epson etc) and 4-color silk screen. In color theory 4-color printing actually should be 3-color printing since you should be able to build any color with these three primary colors. But, as we all learned in kindergarden – adding together C(cyan) M(magenta) and Y(yellow) produces brown! K(black) is added to help print black areas of a color separation because pigments are not always pure and wet ink often does not mix perfectly.
For your print projects with us - your files are best submitted as CMYK files. If needed we CAN accept RGB images and layouts and will do a conversion to CMYK. This can work fine if you primarily work in RGB and don’t want to be troubled with this issue. If however you do a lot of print then you will find that working in CMYK will allow you to have more controlled and predictable results.
Monitor Calibration
Getting a great result with your monitor really is so much easier today than it was even a few years ago. Bulky CRT’s monitors used to color shift very slowly over time so that after a few months (let alone years) the monitor would be far from the starting calibration.
Modern flat screen LCD’s are much more color stable but should still be calibrated monthly. The built in Apple calibration routine is excellent and our staff has been surprised at how close it can match even the most costly “technical” monitors costing over $5,000. Make yourself a sticky note to calibrate your monitor monthly – the results will be worth it!
ICC Printing Profiles
In short – an ICC profile (usually a .icm file) tells your application all about the color gamut or range of the output device. This might be a color laser in your office or a large offset printing press. In Adobe CS3 & CS4 the application has a dialogue box that makes setting all your color options easy to do as a group. The collection of ICC profiles you have chosen to use are saved as a .csf file format.
Step #1 In Photoshop goto >> Edit >> Color Settings (shift command K)
Step #2 Choose “North American Prepress 2” from the top spin bar and you are done!
Once installed and selected – you will find it the default in all the Adobe applications. For files that are properly setup as CMYK either profile (or any profile) will not affect the final printed job. CMYK data is by definition the final format and your values should get transferred to plate and paper exactly as designed. What is does affect is how your layout will appear on screen. It will also become important if you submit RGB files or a mixed job with both CMYK and RGB files. The latter DOES need to convert to CMYK prior to printing and knowing the target gamut is critical to achieving the highest quality. If you have incorrectly chosen a newsprint .csf color profile. This will affect the final print job by reducing the amount of ink resulting in a job that might look “washed out”. Smart graphic designers always like to submit CMYK files so that they know the job will turn out well.
Scanning 101
There will be times when it will be easier to scan something than to recreate from scratch. A few points to remember: Pixels are really “points of information” and you need 300-350 dpi at net size for contone images (photographs). This means that if your file is 300 dpi and you blow it up 200% in Indesign – your net dpi is 150 and you will probably have a softer or less detailed final image. Conversely if you have an image that is 150-200 dpi and you use it at half size – you have effectively DOUBLED the pixel density and your final print should look great! The preferred file format in Photoshop should be 8bit CMYK tiff or photoshop native format. Jpegʼs can be used if desired – just remember that as a “container” for the data – it is great in that it reduces file sizes but you need to pay attention to the compression setting when saving the file format. With many images the “lowest quality” setting will in fact look quite bad! Setting the quality to medium or high will usually result in a good reproduction.
The bad rap that jpegs have gotten as a file format for prepress is the simple fact that each time an image is opened, edited and resaved – a little more “damage” is done to the file! NOT a good file format for images that you might expect to edit frequently or extensively. For a catalog with hundreds of images that have been created with a good color balance - then the CMYK jpeg file format is perfectly fine and would result in a much smaller file format. Again – these days with huge flash drives and fast internet connections file sizes are not such a big priority but it still comes up. It helps to understand your choices. For “line art” scans that might be saved as a bitmap format, 1200 dpi will usually result in clean edges that would be hard to tell from proper vector art. If you have a problem image – please let us know and we will give it some special attention!