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AN1368

Developing Embedded Graphics Applications using PIC ?

Microcontrollers with Integrated Graphics Controller

Author:

Pradeep Budagutta

FIGURE 1:

RED + GREEN = YELLOW

Microchip Technology Inc.

INTRODUCTION

Graphic-enabled devices are used extensively in daily

life. They are found everywhere, including indoor

products, such as telephones, calculators, pagers, MP3

players, digital electric meters, smart remote and UPS

displays. They are also used in outdoor products, such

as traffic signals, taxi meters, bus displays, advertise-

ment boards, etc. The list is virtually endless. A current

trend is that many existing devices are becoming

graphic-enabled because it is economically feasible,

easy to use and the latest in technology.

This application note is intended to help engineers who

are designing their first graphic application. It describes

the basic definitions and jargons of graphics applications

and it helps the engineer to understand the theory,

necessary decision factors, hardware considerations,

available microcontrollers and development tools. Soft-

ware libraries and support are available from Microchip

with further literature references for advanced users.

BASICS OF COLOR SCIENCE

In its purest form, color is associated with the

wavelength of light, within human visible range, from

about 400 nm (Violet) to 700 nm (Red), with Yellow

centered at about 575 nm. That means, if a light of

575 nm wavelength is incident on human eyes, it is

perceived as a Yellow light. We have also learned that

colors can be derived from three basic colors: Red,

Blue and Green. For example, Yellow can be derived

by mixing Red and Green lights. Is this true? The

answer is both no and yes. It is no because mixing Red

and Green lights will constitute a mixture of lights with

wavelengths of 700 nm and 560 nm, and there is not a

wavelength representing Yellow. The answer is yes

because human eyes perceive this mixture as a Yellow

colored light. Therefore, we see the mixture of Red and

Green lights as a single Yellow light, as shown in

Figure 1 . This is due to the color recognition properties

of the human eye.

? 2011 Microchip Technology Inc.

Human eyes perceive the light as a Yellow colored light

instead of separate Red and Green colored lights. This

color recognition property of the human eye is the

foundation of the RGB (Red, Green and Blue) model.

The model states that the human eye can be made to

perceive different colors by mixing appropriate

proportions (intensities) of Red, Blue and Green colors.

Therefore, a ‘colored’ light can be formed by mixing

different proportions of Red, Green and Blue colors.

? Mixing the same proportions of three RGB colors

gives a Gray color

? Mixing a zero amount of all RGB colors gives a

Black color

? Mixing a maximum amount of all RGB colors

gives a White color

Varying the intensity of light, while keeping the same

proportion of RGB, gives different shades of Gray,

which is also known as ‘Grayscale’. Using a single

color (a fixed proportion of RGB) throughout an appli-

cation gives a ‘Monochrome’ application, meaning a

single color.

Since everything is represented in bits and bytes in a

digital system, then how can actual colors be repre-

sented as a number in the form of bits or bytes? Each

of these three basic colors (RGB) can represent a byte

for a number ranging from 0 to 255. Therefore, with

3 bytes, we can represent 16 million colors (2 24 ) and

this is termed as “True Color”. It is also common to use

16 bits to represent colors. With 16 bits, we can

represent 64K colors (2 16 ), which is sufficient for many

graphics applications.

DS01368A-page 1

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