Choosing Colors For Your Images and Documents
Many reasons exist for planning your color choices ahead of time when you're about to begin to create or edit an image for publication either in print or for an on-screen presentation such as display on the World Wide Web (WWW) or an intranet, or for use in a multimedia presentation. The following questions should be taken under consideration before you begin to create or edit an image or document.
We are going to explore some of the factors that will influence how you create or edit your image, keeping these questions in mind.
Color is named or described in many ways. The common methods of describing colors are RGB (Red, Green & Blue), HSL (Hue, Saturation and Lightness or Luminosity), HMS (Highlight, Midtone, Shadow), and CMYK (Cyan, Magenta, Yellow, and K=Black). The two we will focus on the most for this session are RGB and CMYK. These methods of describing colors are called color models.
Left: CMYK Color Model Right: RGB Color Model Note that when CMY are mixed, it creates black. When RGB are mixed, it creates white. Black is created in the RGB model by a total absence of the 3 colors. (R=0, G=0, B=0)
The CMYK color model is used most often for printed documents. Most out-of-house print services often require that format because during the print process, a color plate for each of the 4 colors in the process is produced. Most imaging software, including Paint Shop Pro® allows for CMYK color separations and/or creation using the CMYK model.
The numbers of colors used in the image or document most often influences the cost of a print job out-of-house. For example, a typical black-only newspaper ad might cost in the neighborhood of $50-100. Add a single color, such as red, and the cost jumps by $50 or so!
The CMYK color model can't produce rich and vibrant greens and blues, for example. These colors are known as "out-of-gamut".
The CMYK color model is not precise enough for certain jobs, such as when the consistency of the color is important. An example might be a company logo or trademark. The colors in a logo or trademark must be consistent no matter where or how many times it is printed. Using a color-matching system, such as Pantone®, Dicolor®, Focaltone®, or Trumatch® is a perfect solution for this problem. In a color-matching system, colors are pre-mixed, so only one ink is required. These colors remain true no matter where or when they are printed. Remember, however, that each of these colors would require a plate of its own, so printing costs can become high if too many of these colors are used.
Using a color matching system, such as Pantone®, is simply a palette of pre-mixed colors that will print consistently. Most color-matching systems come with swatch books, or collections of chips that you can choose colors from. These swatches and chips are highly accurate representations of the actual print color on paper.
If you were printing in a single color (for example, a green defined as C=8%, M=0%, y=100%, K=30%), you would have to pay for 3 color plates. By using a color-matching system's color, you would just pay for the single plate.
Inkjet printers are now available for desktop use that use a separate C, M, Y, and K ink cartridges. Some models are available today that have as many as 8 separate color cartridges that include both light and dark C, M, and Y and matte and special photographic black ink. Along with enabling the printing of extremely high-quality images, this is actually cost saving in the long run as you replace the individual cartridges when they become empty. The more standard RGB color printers use a single color cartridge which is divided into "wells", each holding red, green (which is yellow!) and blue inks. Older model printers use color ink to mix black rather than using the black ink cartridge if color printing is specified. This uses your expensive color ink up rapidly, as black is our most-used color. Also, the black produced by mixing is not "true". If you have done a lot of printing that contained only shades of blue, for example, it is likely that the blue "well" will run dry, leaving only red and yellow ink. Most printer manufacturers recommend replacing the cartridge when this happens, so you wind up throwing away good red and yellow ink. The printer would no longer be able to follow the color-mixing commands, nor be able to mix black, our most-used color.
Choosing Colors for Screen Presentations
Using RGB or HSL colors gives you a much broader spectrum of available colors to use in your images for on-screen presentation. These include the "out-of-gamut" colors in the CMYK model we learned about previously.
The monitors we use for viewing on-screen presentations use red, green, and blue phosphors to display colors. For this reason, the RGB or HSL color model should be used for screen graphics. Both allow for 24-bit color display, enabling the 16.7 million colors necessary for photographic display.
Knowing your viewing audience's capabilities (or not!) is another factor in deciding what type of graphic and how many and what colors to use. If you're designing for the company's intranet, and you know that some users have Mac's, others use Windows and still others Unix boxes, but everybody is using Netscape to view the intranet content, it might be advisable to design within the Netscape 216-color "web-safe" palette to assure a more consistent viewing experience for your audience. When you're designing for the Internet, you have no real way of knowing what equipment your viewing audience will have, nor what software or version of that software they're using. I think today it is safe to say that using colors from the 4096-color-cube palette may afford some viewing consistency.
Photographs typically require millions of colors to display well. This is a primary reason for choosing a 24-bit color model (RGB, HSL) and a file format such as .jpg or .png. However, if you might also need to print the graphic, save a copy in a file format that uses a "loss-less" form of compression, such as Run Length Encoding (RLE) or LZ-77, such as .TIFF. Artifacts left from over-compression in a .jpg image cause the printed image to look fuzzy or distorted.
Another point I'd like to bring up is about using anti-alias in your image, particularly as it pertains to text. Since the anti-alias blends the colors from the selection into the background color around it, text which uses anti-alias often prints blurry. Crisp and clean printed text requires no anti-alias be used. Often the software you use, or the printer driver itself renders smooth edges to the text without blurring it. While the text may appear "jagged" on-screen, it will not print that way.
DPI stands for "Dots Per Inch". The DPI of your image is far more important if it is being created for print. They typical monitor today can display at only 72-100 DPI,with 96 being the most common. Therefore, when designing for the WWW or other screen presentations, a DPI setting within that range makes sense. A pixel (PIcture ELement) is the term used for that one-dot display, so you may also hear the term PPI (Pixels Per Inch). It also makes sense when designing for screen presentation to use "pixels" as the default unit of measurement in your drawing.
Creating images for prints has a more difficult set of considerations, many of which are hardware and /or software related.
Older printers generally were able to print at 150 dpi in draft mode and 300 dpi in document mode. Color often wasn't an issue.
The advent of the bubble jet and inkjet printers brought dpi to new standards, where 360 dpi is draft mode and 1440 (or much higher!) is "high" or "photo quality" mode. Today's inkjet printers often have very high photo-quality DPI settings of 2880 and higher. They can provide extremely realistic photo prints. Some desktop models come pre-programmed with color-matching models. If you select that same model or palette in your image editing software, you can be sure that the colors you chose on-screen are the same as those that will print.
This is a good time to mention monitor gamma. When designing for print, it is desirable that the colors you choose on-screen are the same that come out of the printer!
Setting the monitor gamma in your editing software before beginning the design will help assure this happens.
*Reminder: Don't forget to set the monitor gamma back to the default setting of 1.0 before working on screen presentation graphics!
You naturally will want to closely match DPI settings between the image and the DPI you will print at. However many printer drivers interpret differently. Check the printer's documentation to see what DPI they might recommend for an image that is to be created for print at the printer's various resolution settings. The figure is roughly ½ of each DPI setting of the printer. If I print at 360 DPI, I create (or scan) at 150dpi. At 720, the number is 300. At 1440, it is 600. These figures will and do vary between printer manufacturers and often between model numbers of the same brand.
Sometimes a printer's resolution is expressed in LPI (Lines Per Inch). The following chart can be used as a rough guideline for determining the IMAGE resolution based upon either DPI or LPI. Note that the IMAGE resolution is approximately twice that of the LPI.
Other Color Considerations
When creating an image either for print or an on-screen presentation considerations other than the technical kinds we explored come into play.
Throughout our lives we all have millions of experiences which lead us to prefer certain colors. Our own personal preferences often "color" our creations. This is fine provided you don't fall into the trap of designing EVERYTHING under EVERY circumstance in ONLY shades of federal blue and mauve.
Any of you reading this who do design work or do desktop publishing work for hire have quickly learned that you must understand your client's preferences. You have to move past your own preferences even if you think the final result looks like the cat hawked it up with a bonus fur-ball.
All of us have also learned to make color associations as well. When someone mentions "Christmas", most Americans would think of red, green, and white. If Easter were mentioned, most would associate spring-like pale pastel shades. However, were you a member of the clergy, you might instead think of a deep royal purple and gold, the liturgical colors for the Easter season.
It has been well documented that color influences mood. Red often reminds people of anger. Blues can be soothing. White is often considered to be a clean or pure color. Black is often associated with evil. Being in an environment that is shades of black can lead to feelings of loneliness and depression. But we have to keep our cultural divergences in mind, too. While white represents goodness and purity in our culture, in many other cultures it symbolizes death and/or evil. In some cultures, purple is a "royal" color--dignified and used ONLY for the royal family. In other cultures, purple is the color associated with the "ladies of the evening", so you need to know your audience when choosing your colors. This is a most important consideration for WWW work, since it is likely you will have many international visitors.
The last consideration in choosing colors I will mention is "What is the purpose of the image being created?" Here are some questions you can ask yourself while planning your design:
Despite the length of this article, I have but touched upon the reasons why we make choices about the colors we use (or should use) in our images and documents. My hope is that I have at least given you some things to think about BEFORE you begin creating them!