Page 40 - DCAP504_Computer Graphics

Unit 3: Overview of Graphics I/O Devices

Today, the most commonly used graphics memory is between 8 MB and 64 MB and resolutions are
between 800 x 600 and 1024 x 768.
3.5.4 Refresh Rate

The term “refresh-rate” refers to the display screen which is being updated and refreshed. For a stable
flicker-free picture at least 70 refreshes per second is recommended (For every “refresh” the picture on
your monitor is re-drawn). A refresh rate of 50 updates per second gives you a more 'flickery' display.
The “refresh-rate” is measured in Hz (Hertz). (1Hz = 1 time per sec) Horizontal Sweep Frequency
however, refers to the amount of horizontal pixel-lines that the monitor can output per unit. For
example, a resolution of 640 (width) x 480 (height) means that the screen consists of 480 horizontal lines
that are 640 pixels wide each. The Horizontal Sweep Frequency (measured in kHz=kilohertz) tells you
how many of these horizontal lines the monitor draws every second. This job is done by your monitor,
therefore, even if you have a very expensive graphics card in your computer, it is still the monitor that
sets the upper limit for the quality of your display.
3.5.5 The Megapixel Evolution
A pixel is the most basic unit of the image and it is single point of the raster image. Generally, the pixels
are arranged in rows and columns. The different pixels are combined together to form an image. The
pixels vary in brightness and color values. Three components are used to represent the color image and
each component is called as sub pixel. The sub pixel represents the single color that can be red or green
or blue. The information is represented in the bits. Bits per pixel are the number of bits of information
reserved per pixel of an image. Usually the digital images are made up of many pixels. One million
pixels constitute the megapixel. The pixel density is the number of pixels per unit area on the sensor.
The different cameras have different pixel density. Both megapixel count and pixel density are related.
The smallest megapixel count corresponds to a very high pixel density. The resolution of an image
depends on the pixels.
Elements of picture quality
The megapixel is one aspect that plays an important role in the quality of the camera or the photo that it
produces. In addition, the camera sensor and optical quality of a lens play an important role in the
quality of an image.
Apart from the sensor and lens, other elements that determine the quality of photos are:
• Appropriate lighting on a subject.
• Proper focus

• Taking a photo at high resolution

In the case of a 16 by 24 foot image and in such case, the megapixels do not detect the
Did you know?
clarity of the image. It depends on the lens and sensor of the camera.

Image resolution is the number of pixels that are counted horizontally or vertically in describing the
image.
Let us now understand basicity in megapixel evolution. Digital cameras play an important role in
today's growing world. The digital photography helps in taking the images. These can be uploaded to
the computer within no time.
A camera is a lightproof box that allows a certain amount of light to enter at the right time. A
photographic film is present inside the camera. The image is formed when light enters the box. This is
because a chemical reaction takes place on the photographic film. The camera flash is used to light up a
scene that is too dim so that it is clear on the film. Earlier, flash bulbs were used to burn magnesium
metal with a brilliant white light. However, modern cameras use electric currents that moves through
xenon gas and causes the gas to glow light.
The photographic film is coated with silver halide solution that is light sensitive. Hence, when light falls
a chemical change in the silver halide crystals occurs. This reaction helps in the formation of the latent

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