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© 2 Print and Save 2009

How to Convert RGB Files to CMYK

CMYK stands for the four colors used for four-color process printing
(cyan, magenta, yellow and black).
RGB is the color space typically used on computer monitors and stands for red (R), green (G) and blue (B). RGB are the primary colors of light.

Because CMYK is expressly designed for the four-color printing process, we need you create your documents in this color space.

If you send us an RGB file, we can convert it to CMYK. However, this standard value conversion may not yield the result you are looking for. RGB looks good on a computer monitor but tends not to produce the same results when printing. CMYK is a better approximation of how colors will look in print.

Please note that while we print every project in keeping with "pleasing color" standards, we make no guarantee that the color you see on your computer monitor or your color printer will approximate your finished piece printed via the CMYK process. Wide variation in color spaces, technologies and calibrations of different monitors and printers may preclude an exact match. If color accuracy is important to your project, we recommend reviewing a high quality color proof.

There are colors you may see in RGB that cannot be made with CMYK. They are considered by the translator as "out of the CMYK color gamut" and the translator comes as close as possible to matching the original. While this may be less noticeable in an image, it is more noticeable for colors used in type or solid color areas. Therefore, we recommend you select colors for fonts or other design elements in the layout using CMYK definitions. This will give you a better idea of how your printed pieces will look.

Following is a list of several common design and publishing programs with instructions on how to make sure you are working in the CMYK color space.

Microsoft Publisher

Microsoft Publisher defaults to RGB. To convert or start a document in a 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, not embedded, in order to maintain the CMYK color space within the image. You can accomplish this by following these menu options: 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. Don't forget to send us both the images and the layout file.

Adobe Photoshop
For an existing file, select the following menu options: Image/Mode/CMYK. When starting a new file, select CMYK for the mode before clicking OK.

Use the following menu options to convert or create files with CMYK: Edit/Edit Colors/Show Colors in Use/Highlight Color and click Edit. Change model to CMYK and deselect Spot color.

Adobe Illustrator
For an existing file, select the following menu options: Edit/Select All and then Filter/Colors/Convert to CMYK. For a new file, select File/New and select CMYK color for the Color Mode.

Corel Draw
Select 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. Make sure you export everithing under Adobe Gamma.

Adobe InDesign
For new or existing documents, use 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 as well. Select each object you want to convert and make sure the Color palette reflects the CMYK percentages. Click the top right arrow in the palette to change to CMYK if necessary.

Adobe PageMaker
Use the following menu options: Window/Show Colors. Double click "Colors" in palette and select Model to be CMYK and Type to be Process. Please note that PageMaker does not successfully represent CMYK color on the monitor.

Bitmap Vs Vector files
Graphic images that have been processed by a computer can usually be divided into two distinct categories. Such images are either bitmap files or vector graphics. If you work in prepress, you need a good comprehension on the advantages and disadvantages of both types
As a general rule scanned images are bitmap files while drawings made in applications like Corel Draw or Illustrator are saved as vector graphics. But you can convert images between these two data types and it is even possible to mix them in a file. This sometimes confuses people. of data.

Bitmaps images
are exactly what their name says they are: a collection of bits that form an image. The image consists of a matrix of individual dots (or pixels) that all have their own colour (described using bits, the smallest possible units of information for a computer).

Here you see an image and to the right top a 250 percent enlargement. As you can see the image consists of hundreds of rows and columns of small elements that all have their own colour. One such element is called a pixel -short for picture element). The human eye is not capable of seeing each individual pixel so we perceive a picture with smooth gradations.

The number of pixels you need to get a realistic looking image depends on the way the image will be used. .

Types of bitmap images
Bitmap images can contain any number of colours but we distinguish between four main categories:

These are images that only contain two colours, usually black and white. Sometimes these images are referred to as bitmaps because a computer has to use only 1 bit (on=black, off=white) to define each pixel.

Grayscale images
contain various shades of grey as well
as pure black and white.


This images contain shades of two or more colours. The most popular multitone images are duotones, which usually consist of black and a second spot colour (often an Pantone colour).

Full colour images

The colour information can be described using a number of colour spaces: RGB, CMYK or Lab for instance.

Characteristics of bitmap data
Bitmap data can take up a lot of room. A CMYK A4-size picture that is optimized for medium quality printing (150 lpi) takes up 40 MB. Compression can reduce the size of the file.

Oone of the main disadvantages of bitmap images: once they are enlarged to much, they look unnatural and blocky. But reducing a picture too much also has a bad influence as it looses sharpness.
Bitmaps are fairly simple to output, as long as your RIP or printer has sufficient memory.

There are hundreds of applications on the market that can be used to create or modify bitmap data. In prepress Adobe PhotoShop, are the best.

Bitmaps File formats
Bitmap data can be saved in a wide variety of file formats. Among these are:

  • BMP: limited file format that is not suitable for use in prepress.
  • EPS: flexible file format that can contain both bitmap and vector data.
  • GIF: mainly used for internet graphics
  • JPEG: or rather the JFIF file format, which is mainly used for internet graphics
  • PDF: versatile file format that can contain just about any type of data including complete pages, not yet widely used to exchange just images
  • TIFF: the most popular bitmap file format in prepress

Vector graphics
are images that are completely described using mathematical definitions.
To the left you see the image itself and to the right you see the actual lines that make up the drawing.

Each individual line is made up of either a vast collection of points with lines interconnecting all of them or just a few control points that are connected using so called bezier curves. It is this latter method that generates the best results and that is used by most drawing programs.

Characteristics of vector drawings

Vector drawings are usually pretty small files because they only contain data about the bezier curves that form the drawing.
The filesize of this preview image is usually larger than the actual bezier data themselves.

Vector drawings can usually be scaled without any loss in quality. This makes them ideal for company logo's, maps or other objects that have to be resized frequently. Please note that not all vector drawings can be scaled as much as you like:

  • Drawings containing trapping information can only be scaled up to 20 percent larger or smaller.
  • Thin lines may disappear if a vector drawing is reduced too much.
  • Small errors in a drawing may become visible as soon as it is enlarged too much.

It is fairly easy to create a vector based drawing that is very difficult to output. Especially the use of tiles (small objects that are repeated dozens or hundreds of times) and Corel Draw lens effects can lead to very complex files.

There are hundreds of applications on the market that can be used to create or modify vector data. In prepress, Adobe Illustrator and Corel Draw are the most popular.

Vector File formats
Bitmap data can be saved in a wide variety of file formats. Among these are:

  • EPS, AI, CDR : popular files formats to exchange vector drawings although EPS-files can also contain bitmap data.
  • PDF: versatile file format that can contain just about any type of data including complete pages.