Researching specific details how to back-up my own learning and developments of how to convert RGB files to CMYK (converting screen-based design to print-ready design, and, of course, vice versa) for my 'What Is Design for Print?' ISSUU publication manual. Developments of this project can be, of course, found on this Design Context blog- and my Design Practice blog.
Several site converters- not exactly what I was looking for (looking more in terms of software conversions,) but an interesting resource nevertheless!
Important Information About RGB and CMYKMany graphics software programs give you the choice to work in either RGB or CMYK. These are called "color spaces". Scanners and digital cameras create images using combinations of just three colors: Red, Green and Blue (called "RGB"). These are the primary colors of light, which computers use to display images on your screen. Printing presses print full color pictures using a different set of colors, the primary colors of pigment: Cyan (blue), Magenta (red), Yellow and Black (called "CMYK"). This is "4-color process" or "full-color" printing that comprises the majority of magazines and marketing materials you see every day. At some stage your RGB file must be translated to CMYK in order to print it on a printing press.
It's Best If You do the RGB-to-CMYK Conversion of Your ImagesYou will have more control over the appearance of your printed piece if you convert all of the images from RGB to CMYK before sending them to us. When we receive RGB images, we do a standard-value conversion to CMYK, which may not be perfectly to your liking. We want you to be happy, so please, take the time to prepare your file properly. We cannot be responsible for sub-par results if you furnish your images in RGB. Even though monitors always use RGB to display colors, the colors you see on your monitor will more closely match the final printed piece if you are viewing them in the CMYK color space.
Be aware that it is possible to see colors in RGB that you can't make with CMYK.They are said to be "out of the CMYK color gamut". What happens is that the RGB-to-CMYK translator just gets as close as possible to the appearance of the original and that's as good as it can be. It's something that everyone in the industry puts up with. So it's best to select any colors you use for fonts or other design elements in your layout using CMYK definitions instead of RGB. That way, you will have a better idea of how they will appear in your printed piece. Here's a common example: many programs translate the 100% Blue in RGB into a somewhat purple-looking color in CMYK. We recommend a CMYK value of 100-65-0-0 to get a nice clean blue. Working in the CMYK color space allows you to select the CMYK recipe, or "screen build", that gives you the results you want. Here are some examples of how various RGB colors convert to CMYK:
You most likely won't notice this kind of color shift in a color photograph.It is more likely to happen if you pick a very rich, vibrant color for a background or some other element of your layout. It probably won't look bad, it just won't look exactly the same. But it may not be noticeable at all either.
To purchase a color guide with over 3,000 process colors and their CMYK screen percentages visit the CreativePro Pantone store.
Converting to the CMYK Color SpaceHere is a list of several common programs with instructions on how to make sure you are working in the CMYK color space. If your program or version is not listed here, don't worry. Most of these instructions will apply to all versions of a program. If at any time you need further help, please call us for assistance. We are happy to talk you through the steps needed to get your document into the CMYK color space.
Microsoft Publisher 2000Microsoft Publisher defaults to RGB. It is easy to convert everything to a CMYK color space or to start a new document using the CMYK color space. Use the following menu options: Tools/Commercial Printing Tools/ Color Printing and select Process colors (CMYK). Please note that all images incorporated into a layout need to be linked and not embedded in order to maintain the CMYK color space within the image. Using the following menu options does this: Tools/Commercial Printing Tools/Graphics Manager and highlight the embedded image. Click Link and click Browse to locate the original file and link to it. You will then need to send both the images and the layout file to us for printing.
Microsoft Publisher 2003-2007 or laterSelect File Tab, then select Info. Select Commercial Print Settings. Select Choose Color Model, then Select Process Colors (CMYK)
Adobe PhotoshopIf the file already exists select the following menu options: Image/Mode/CMYK When starting a new file select CMYK for the mode before clicking OK.
Corel Draw 9Select each object you want to convert. Select the Fill tool and click Fill Color Dialog. Make sure the Color model is CMYK. For each object with an outline: Select the Outline tool and click the Outline Color Dialog. Make sure the Color model is CMYK.
Adobe IllustratorSelect File/Document color mode/CMYK color
Quark Xpress 4.1Use the following menu options: Edit/Edit Colors/Show Colors in Use/Highlight Color and click Edit. Change model to CMYK and deselect Spot color. Remember to send us your layout and linked images!
Adobe InDesignUse the following menu options: Window/Swatches and Window/Color. Double click color in Swatches Change color mode to CMYK and color type to Process. Any colors created in the document that are not in the Swatches palette, need to be changed to the CMYK color space. Select each object you want to convert and make sure the Color palette reflects the CMYK percentages. Click top right arrow in the palette to change to CMYK if necessary. Remember to send us your layout and linked images!
Adobe Pagemaker 6.5Use the following menu options: Window/Show Colors. Double click "colors" in palette and select Model to be CMYK and Type to be Process. Please be advised that Pagemaker does not successfully represent CMYK color on the monitor.
The following programs do not have the capability to convert to CMYK. No worry, we will convert it for you free of charge!
If you do not see your program listed here, or are having difficulty converting RGB to the CMYK color space,
please call us at 1-800-930-6040 for further assistance.
How to Convert RGB to CMYK in Photoshop
When you take a photograph with a digital camera or scan an image using a digital scanner, the resulting file will use the RGB (Red Green Blue) colour space. You can then view it on your computer monitor and print it out using your desktop printer and get a good representation of the colour in the original image; this is because your monitor and printer use the same RGB colour space.
If you need to have your photograph printed by a commercial printer using 'full colour process printing', you will have to covert RGB files to CMYK, as a printing press uses the CMYK (Cyan Magenta Yellow blacK) colour space.
The problem is; the range of colours, referred to as gamut, that can be produced using CMYK colour inks on paper, is a lot smaller than what can be represented using RGB. This can result in a photograph printing with some of the colours changing hue and looking dull. This often happens to the bright rich blue found in sky areas of an image.
The image below left is the original RGB, to the right, the image has been converted to CMYK. Notice the colour shift. The larger photo has been adjusted slightly to bring out the colour.
We have a further problem. There is no standard fixed CMYK gamut; so the same percentages of CMYK inks will not always produce the same colour. There are variations in the inks, the absorbency of the paper, the printing conditions, and different press setups which vary in different parts of the world.
The black ink in CMYK printing is used because the CMY inks do not produce a pure black when added together: they produce a brown colour due to impurities in the inks. The black ink when added gives more contrast to the image with darker shadow areas.
It is possible to replace any grey areas of an image (represented by equal amounts of CMY inks) with an equivalent percentage of black ink, thus reducing the amount of ink used. This is referred to as undercolour removal (UCR).
Therefore, there are many possible combinations of CMYK to achieve the same image as in the original RGB file.
Converting RGB files to CMYK
Thankfully, Adobe Photoshop, Illustrator and InDesign, are design programs that provide CMYK Prepress presets recommended for press setups across the world.
In Photoshop, select 'Edit' then 'Color Setting...' and look at the dropdown list under 'Settings'. Here you will see presets for Europe, North America and Japan.
Select a CMYK profile that best suites the final printing conditions, for example, 'ISO Coated v2 (ECI)', which is used for standard ISO printing based on the FOGRA39L characterization dataset applicable to reference printing conditions according to the international standard ISO 12647-2:2004.
Clicking on the 'More Options' button will allow you to set the rendering intent to use when converting from RGB values to CMYK. For continuous tone images such as photographs, selecting 'Perceptual' will generally give the best results while preserving the visual relationships of the source image.
Once you have setup the best colour settings above, you can open the RGB image you want to convert.
A photograph from a digital camera will probably have an embedded RGB colour profile (sRGB IEC61966-2.1). If Photoshop presents a window with 'Embedded Profile Mismatch' then select 'Use the embedded profile'.
If you need to make any adjustments to the image or apply any filters etc., do it now while the image is still in the RGB colour space.
To see which areas of the image that are 'out of gamut'; select 'View' - 'Gamut Warning'. Any colours that turn grey are colours that can not be produced in the CMYK colour space and Photoshop will have to select the nearest colour it can, depending on the rendering intent you selected earlier.
To covert from RGB to CMYK; select 'Image' - 'Mode' - 'CMYK Color'. You will probably notice that some of the colours change and become much duller. As shown in the images above. Here the colour of the sky has changed dramatically from a bright saturated blue to a duller purplish blue.
It is possible to fine tune the CMYK image to improve the colour of the sky and make it a brighter blue. To arrive at the larger image above, I used Photoshop's 'Replace Color' adjustment tool, selecting the sky colour and adjusting the saturation, lightness and hue controls.