November '20

Issue link:

Contents of this Issue


Page 58 of 118

S I G N A G E & P R I N T I N G T H E D I G I T A L E Y E | S T E P H E N R O M A N I E L L O MEASURING COLOR DETERMINING THE BEST COLOR VALUES 5 4 G R A P H I C S P R O N O V E M B E R 2 0 2 0 G R A P H I C S - P R O. C O M L ight is certainly a mysterious phe- nomenon. The light that sur- rounds us is composed of photons whose behavior exhibits properties of both waves and particles. We are con- stantly bombarded by photons all day, every day from the time we are born until the time we die. Photons illuminate the visible universe. Since graphics professionals are de- pendent on the manipulation of light, I thought it would be interesting to ad- dress the dynamics of how light is mea- sured and how those measurements are used to produce the best possible images for both print and digital applications. LIGHT PATH Light is a continuous stream of en- ergy. When light shines on an object, it is reflected into the human eye. It then migrates through a transparent disc called the cornea, through a lens, and onto a surface called the retina where it is converted into electrical im- pulses and migrates through a chan- nel called the optic nerve into a bun- dle of nervous tissue called the brain. The digital camera is a mechanical rep- lica of the eye having a lens (the cornea), a sensor (the retina), a cable (the optic nerve), and a computer (the brain) (Fig- ure 1). The similarities between these two de- vices are pretty obvious, but the differ- ences are profound. Where the eye sees a continuous and seamless fabric of color and tone, the digital camera divides the colors and tones into little squares called pixels. A photosensitive array of colored filters separates light into three basic col- ors: red, green, and blue (Figure 2). The sensor records the strength of each color component, and special software assigns a specific numerical value to each square. The red, green, and blue values are then assigned to individual pixels, which when viewed, display the mixture of the three colors. BIT DEPTH Each pixel contains a quantity of infor- mation that determines its quality, or in the parlance of the digital world, its bit depth. Pixels of smaller bit depths dis- play fewer colors. I think the best way to understand how colored light is trans- lated into the numbers that a computer can understand is to look at the simplest color model as an example. Bitmap images (Figure 3)—not to be confused with bitmap format—have one bit of information and produce pixels that are either black or white. Computers use a binary number system to make calcula- tions. Unlike the common decimal system that has 10 characters, a binary number system uses just two characters, 0 and 1, to represent all of the numbers. It helps to think of each pixel in a bit- map as a light switch. The switch is either Figure 1. The structure of the eye and the camera are similar. (All images courtesy Stephen Romaniello) Figure 2. A photo-sensor uses an array of colored filters to separate light into three basic color components: red, green, and blue.

Articles in this issue

view archives of GRAPHICS PRO - November '20