RGB Color

A nostalgic look back at graph paper helped us learn the fundamentals for pixel locations and size. Now that it is time to study the basics of digital color, we search for another childhood memory to get us started. Remember fi nger painting? By mixing three “primary” colors, any color could be generated. Swirling all colors together resulted in a muddy brown. Th e more paint you added, the darker it got. Digital colors are also constructed by mixing three primary colors, but it works differently from paint. First, the primaries are diff erent: red, green, and blue (i.e., “RGB” color). And with color on the screen, you are mixing light, not paint, so the mixing rules are diff erent as well.

  • Red + Green = Yellow
  • Red + Blue = Purple
  • Green + Blue = Cyan (blue-green)
  • Red + Green + Blue = White
  • no colors = Black

This assumes that the colors are all as bright as possible, but of course, you have a range of color available, so some red plus some green plus some blue equals gray, and a bit of red plus a bit of blue equals dark purple. While this may take some getting used to, the more you program and experiment with RGB color, the more it will become instinctive, much like swirling colors with your fi ngers. And of course you can’t say “Mix some red with a bit of blue, ” you have to provide an exact amount. As with grayscale, the individual color elements are expressed as ranges from 0 (none of that color) to 255 (as much as possible), and they are listed in the order R, G, and B. You will get the hang of RGB color mixing through experimentation, but next we will cover some code using some common colors.



Example 1-3: RGB color

background(255);  
noStroke();  
fill(255,0,0); 
ellipse(20,20,16,16);  
fill(127,0,0); 
ellipse(40,20,16,16);  
fill(255,200,200); 
ellipse(60,20,16,16);  

Processing also has a color selector to aid in choosing colors. Access this via TOOLS (from the menu bar) → COLOR SELECTOR.

Exercise 1-5: Complete the following program. Guess what RGB values to use. Feel free to use the color selector.

fill(________,________,________);  // Bright blue
ellipse(20,40,16,16); 
fill(________,________,________);  // Dark purple 
ellipse(40,40,16,16); 
fill(________,________,________);  // Yellow 
ellipse(60,40,16,16); 

Answer key

Exercise 1-6: What color will each of the following lines of code generate?

fill(0,100,0);     ______________________________________  
fill(100);         ______________________________________  
stroke(0,0,200);   ______________________________________  
stroke(225);       ______________________________________  
stroke(255,255,0); ______________________________________  
stroke(0,255,255); ______________________________________  
stroke(200,50,50); ______________________________________    

Answer key

Color Transparency

In addition to the red, green, and blue components of each color, there is an additional optional fourth component, referred to as the color’s “alpha.” Alpha means transparency and is particularly useful when you want to draw elements that appear partially see-through on top of one another. Th e alpha values for an image are sometimes referred to collectively as the “alpha channel” of an image.

It is important to realize that pixels are not literally transparent, this is simply a convenient illusion that is accomplished by blending colors. Behind the scenes, Processing takes the color numbers and adds a percentage of one to a percentage of another, creating the optical perception of blending. (If you are interested in programming “ rose-colored ” glasses, this is where you would begin.)

Alpha values also range from 0 to 255, with 0 being completely transparent (i.e., 0% opaque) and 255 completely opaque (i.e., 100% opaque).

Example 1-4: Alpha transparency

background(0);
noStroke();

// No fourth argument means 100% opacity.
fill(0,0,255);
rect(0,0,100,200);

// 255 means 100% opacity.
fill(255,0,0,255);
rect(0,0,200,40);

// 75% opacity.
fill(255,0,0,191);
rect(0,50,200,40);

// 55% opacity.
fill(255,0,0,127);
rect(0,100,200,40);

// 25% opacity.
fill(255,0,0,63);
rect(0,150,200,40);

Custom Color Ranges

RGB color with ranges of 0 to 255 is not the only way you can handle color in Processing. Behind the scenes in the computer’s memory, color is always talked about as a series of 24 bits (or 32 in the case of colors with an alpha). However, Processing will let us think about color any way we like, and translate our values into numbers the computer understands. For example, you might prefer to think of color as ranging from 0 to 100 (like a percentage). You can do this by specifying a custom colorMode().

colorMode(RGB,100);

The above function says: “OK, we want to think about color in terms of red, green, and blue. The range of RGB values will be from 0 to 100.”

Although it is rarely convenient to do so, you can also have different ranges for each color component:

colorMode(RGB,100,500,10,255);

Now we are saying “Red values go from 0 to 100, green from 0 to 500, blue from 0 to 10, and alpha from 0 to 255.”

Finally, while you will likely only need RGB color for all of your programming needs, you can also specify colors in the HSB (hue, saturation, and brightness) mode. Without getting into too much detail, HSB color works as follows:


  • Hue — The color type, ranges from 0 to 360 by default (think of 360 degrees on a color “wheel”).
  • Saturation — The vibrancy of the color, 0 to 100 by default.
  • Brightness — The, well, brightness of the color, 0 to 100 by default.

With colorMode() you can set your own color range.


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