Axis 2400+ Instrukcja Użytkownika Pobierz pdf (Strona 28)

Determining factors

The major factors effecting image quality for cameras

can be deﬁ ned as follows:

• The lens

• The optical ﬁ lter

• The image sensor

• The camera’s Digital Signal Processor (DSP)

• The compression standard and its implementation

Varifocal lenses

A good lens is important for achieving high image quality.

Good basic lenses can be found from a few manufacturers,

but note that the basic lenses sourced from these supp-

liers should use glass (not plastic).

Infrared

An optical ﬁ lter is placed between the lens and the

image sensor. Its main purpose is to remove the invi-

sible infrared (IR) light. All image sensors are sensitive

to IR light; without this ﬁ lter the images tend to look

very bad in some environments, e.g. in rooms lit with

normal light bulbs.

Night cameras are not ﬁ tted with this ﬁ lter as it reduces

sensitivity. The ﬁ lter is invariably a piece of glass, but it

may also be built into the lens.

In more expensive cameras an optical low pass ﬁ lter

is added. These reduce the amount of false color that

can occur when the scene contains ‘thin’ details.

Image sensors

Two main image sensor technologies are currently avai-

lable: CCDs and CMOS-sensors. CCDs are more sensitive

in low light conditions and give better dynamics than

CMOS-sensors. CMOS-sensors, on the other hand, pro-

vide alternative camera solutions that are both smaller

and cheaper.

Image quality

If you compare the images from different cameras you will ﬁ nd that the

quality differs considerably between different brands. These quality variations

depend on several factors and are especially noticeable in low light conditions.

A basic mono focal lens.

A high quality vari-focal lens.

An optical IR ﬁ lter.

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Axis 2400+ Instrukcja Użytkownika Strona 28