2 Kinds of Color

Color Models
A color model is an orderly system for creating a whole range of colors from a small set of primary colors. There are two types of color models, those that are subtractive and those that are additive. Additive color models use light to display color while subtractive models use printing inks. Colors perceived in additive models are the result of transmitted light. Colors perceived in subtractive models are the result of reflected light.

The Two Most Common Color Models
There are several established color models used in computer graphics, but the two most common are the RGB model (Red-Green-Blue) for computer display and the CMYK model (Cyan-Magenta-Yellow-blacK) for printing. 

RGB Color Model Additive color model For computer displays Uses light to display color Colors result from transmitted light Red+Green+Blue=White	CMYK Color Model Subtractive color model For printed material Uses ink to display color Colors result from reflected light Cyan+Magenta+Yellow=Black

Source:  www.sketchpad.net

Notice the centers of the two color charts. In the RGB model, the convergence of the three primary additive colors produces white. In the CMYK model, the convergence of the three primary subtractive colors produces black.

In the RGB model notice that the overlapping of additive colors (red, green and blue) results in subtractive colors (cyan, magenta and yellow). In the CMYK model notice that the overlapping of subtractive colors (cyan, magenta and yellow) results in additive colors (red, green and blue).

Also notice that the colors in the RGB model are much brighter than the colors in the CMYK model. It is possible to attain a much larger percentage of the visible spectrum with the RGB model. That is because the RGB model uses transmitted light while the CMYK model uses reflected light. The muted appearance of the CMYK model demonstrates the limitation of printing inks and the nature of reflected light. The colors in this chart appear muted because they are displayed within their printable gamut (see below).

Additive vs. Subtractive Color Models

Since additive color models display color as a result of light being transmitted (added) the total absence of light would be perceived as black. Subtractive color models display color as a result of light being absorbed (subtracted) by the printing inks. As more ink is added, less and less light is reflected. Where there is a total absence of ink the resulting light being reflected (from a white surface) would be perceived as white.

Color Gamut and Color "Space"

Each color model has is own gamut (range) of colors that can be displayed or printed. Each color model is limited to only a portion of the visible spectrum. Since a color model has a particular range of available color or gamut, it is referred to as using a "color space". An image or vector graphic is said to use either the RGB color space or the CMYK color space (or the color space of another color model). Some graphic applications present the user with more than one color model for image editing or illustration and it is important to choose the right one for the task. The whole point of this article is to explain the difference between the two color models so you choose the right one for the job. For you work to display at its best, choosing the right color model is critical.

RGB Color

The RGB model forms its gamut from the primary additive colors of red, green and blue. When red, green and blue light is combined it forms white. Computers generally display RGB using 24-bit color. In the 24-bit RGB color model there are 256 variations for each of the additive colors of red, green and blue. Therefore there are 16,777,216 possible colors (256 reds x 256 greens x 256 blues) in the 24-bit RGB color model.

In the RGB color model, colors are represented by varying intensities of red, green and blue light. The intensity of each of the red, green and blue components are represented on a scale from 0 to 255 with 0 being the least intensity (no light emitted) to 255 (maximum intensity). For example in the above RGB chart the magenta color would be R=255 G=0 B=255. Black would be R=0 G=0 B=0 (a total absence of light).

CMYK or "Process Color"

The CMYK printing method is also known as "four-color process" or simply "process" color. All of the colors in the printable portion of the color spectrum can be achieved by overlapping "tints" of cyan, magenta, yellow and black inks. A tint is a screen of tiny dots appearing as a percentage of a solid color. When various tints of the four colors are printed in overlapping patterns it gives the illusion of continuous tones - like a photograph: The CMYK model forms its gamut from the primary subtractive colors of cyan, magenta and yellow. When cyan, magenta and yellow inks are combined it forms black - in theory. However, because of the impurities in ink, when cyan, magenta and yellow inks are combined it produces a muddy brown color. Black ink is added to this system to compensate for these impurities.         


In the CMYK color model, colors are represented as percentages of cyan, magenta, yellow and black. For example in the above CMYK chart the red color is composed of 14% cyan, 100% magenta, 99% yellow and 3% black. White would be 0% cyan, 0% magenta, 0% yellow and 0% black (a total absence of ink on white paper).

When In Doubt, Save Images As RGB

The RGB model displays a much larger percentage of the visible spectrum than the CMYK model and, as a result, has a wider gamut. Once an image has been converted from RGB to CMYK and brought into printable gamut, the extra RGB data will be lost.

One can retain out-of-gamut areas in CMYK images and leave it to the computer to bring the colors into gamut at printing time. However this requires the computer to make the conversion from RGB to CMYK and this doesn't always work out as well as one might expect. Conversion between color models is not always a good idea.

Because of this fact, you want to scan or shoot images (with a digital camera) using the appropriate color model for their primary purpose. If the images will be used primarily for print then use CMYK. If they will be used primarily for screen displays, then use RGB. You can always convert from RGB to CMYK (or vise-versa) but it is best not to.

If you can afford the time, money and disk space to scan or shoot both versions of an image where both are needed, then this is the best solution. This is especially true if you will be using the same images for both printed material (such as a catalog) and the web (such as an online catalog). A little planning can go a long way here.

But if you are not sure, then I generally recommend saving images in RGB mode and creating CMYK copies for printed material as needed.

Use RGB For Screen Displays and CMYK For Print

It is important to choose the right color model for the job. If your images will be printed, then convert them to CMYK and manually bring them into gamut before printing. If your images are to be displayed on a computer, then make sure you use RGB color so the full gamut will be available for display. Because both models can be available at the same time while using an application, it is easy to make a mistake and choose the wrong palette or set of color swatches.

Desktop Publishing

Desktop publishing (DTP) is generally regarded to have three "legs" or branches - image editing, illustration and page layout. There are many software applications that fall into these categories, but the undisputed leaders of these applications are Adobe® Photoshop®, Adobe Illustrator® and QuarkXPress™. That is the state of affairs as it exists today because these applications are so entrenched in the industry. All responsible instructors will steer students into learning these applications because they want their students to be able to use the tools that are being used.

It is worthy of note, however, that with the recent release of Adobe InDesign®, QuarkXPress's position as undisputed leader for page layout may change. Designers, teachers and students should take a look at this new package and give it serious consideration.

There is one application which is unique in that it does all three at the same time and that is Deneba Canvas™. It is the only program that was designed with the purpose of being able to create and edit bitmap and vector objects concurrent with page layouts and not have to leave the application. This is an exciting product with a lot of potential.

The chart below illustrates the concept. Please do not draw any inferences that one application is better or worse or as good as another or that Canvas is equal to all three. I'm not here to judge them or place one over the other. The point is that these are the functions and these applications are the leaders for these functions.

Source:  www.sketchpad.net

My purpose in pointing this out is to encourage students and professionals alike to learn these applications and obtain the skills to use them.

How I Work - Strategy and Workflow
I will tell you how I work. There are other applications that have more "bells and whistles" and some do things faster and easier than these. I will use any and every application I can to make my work easier. Some effects are only possible in certain applications. What I will try to do is learn what exactly each application can and can't do, how well the files port between each other and which features get lost or altered in the process. That takes a lot of experimentation and practice, but the result is that you can plan a workflow in a correct sequence and wind up with a good result. That is the strategy behind how I work. One important point to make about file formats is that if a file format doesn't port well between applications, it's not the format that is at fault. Each software vendor writes or obtains its own import and export filters so the results can be quite unpredictable.

Bitmap Images
The Photoshop PSD format is widely supported and ports between most applications easily. However, I avoid using editable text layers until last when I finish the image in Photoshop. Most bitmap formats (TIFF, PCX, BMP, etc.) port without a hitch but I prefer the PSD format because it supports layers. On the PC I use Paint Shop Pro™ for all the screen shots (on the Mac® I use Snapz Pro™ 2). I'll save them as Photoshop PSDs on both platforms. Cropping is fast and easy, I can copy and paste rectangular selections quickly and I prefer it over Photoshop for bitmap editing of GIF files.

Vector Images
Most applications will port generic vector EPS with no problem as long as there are no gradient fills and the image uses solid colors for strokes and fills. There are a lot of clipart images in WMF (Windows® Meta File) format. This format does not support Bezier curves. All "curves" in these files are composed of short, straight line segments. I will use Macromedia® FreeHand® to simplify the paths in these files and convert the straight segments to curves. CorelDRAW® would be my second choice for that job. Now even Canvas 7 has a tool this. A plug-in for Adobe Illustrator 8 called "Smart Remove Points" from BeInfinite, Inc. is available for the Mac. If the application only supports Windows metafiles I prefer to use the EMF (Enhanced Meta File) format over the WMF format because it supports Bezier curves. I have also found that there is wide support for Adobe Illustrator version 7 and that format ports quite well. Even some versions of the CorelDRAW format port well also. I try to avoid passing gradient fills between applications and certainly not any of the special strokes or patterns. I will save those for the final application used to produce the image or composition.

Images With Clipping Paths
As a rule I use Adobe Acrobat® PDF format for porting masked bitmaps between illustration programs. Sometimes EPS images with clipping paths will port with the mask and bitmap intact, but not always. Sometimes the Adobe Illustrator 7 format will work for this purpose. I will always make the final image with a clipping path as an EPS and I will use Photoshop to create the file. Sometimes I will use Illustrator, though. The reason I use an Adobe product to create an EPS file is because EPS files are PostScript® (Encapsulated PostScript) and Adobe is the source of PostScript. I know I can count on a clean file if I do.

Basics in Computer Graphic Design

Computers are getting more powerful by the day and the software vendors are providing mind-boggling applications which constantly push the limits of the hardware. End users are faced with the daunting task of keeping up to date. The graphic artist of yesterday only had to know about the various kinds of print media. Today's graphic artist has to know about electronic publishing as well as print media.

In manufacture there are several graphic design software (software) or software (hardware) that can not be denied again will require a large amount of cost tertutama software that is used must be licensed with the rather expensive price, while for hardwarenya itself but depends on the needs for more setabil specifications required that the rather than to file pengetikan - presentation materials or other.

The following chart shows how all the various parts fit together - vector vs. bitmap graphics, some of the various software applications used to create them (Adobe® Illustrator®, CorelDRAW®, Macromedia® FreeHand®, Adobe Photoshop®, Corel PHOTO-PAINT® and Paint Shop Pro™), the four basic file formats and the two most common color models used in computer graphics for print media and the web: