Pulnix TMC-4200CL Instrukcja Użytkownika Pobierz pdf (Strona 9)

9JAI Vision News

1. Edition 2007

Resolution proportional digital

zoom (RPDZ)

This patent pending technology is available

on new 4 megapixel camera models (TM-

4200CL and TM-4200GE). RPDZ maintains

a constant data rate between the camera

and the host computer while digitally

modifying (zooming) the camera’s field-of-

view (FOV). This is accomplished by sub-

sampling pixels in the image in a manner

proportional to the digital zoom level. For

example, in a 4 megapixel camera (2048

x 2048) utilizing RPDZ, four zoom modes

are offered. The full FOV is imaged by

capturing every fourth pixel in every fourth

row, thus creating a 512 x 512 resolution.

(See fig 3).

As the image is digitally zoomed through

the other three modes, the sub-sampling

rate is adjusted to maintain the same pixel

density until it reaches the center 512 x 512

pixels of the image. The idea is to support

digital zooming in applications like UAVs,

while holding the resolution at a level that

fits within the standard TV bandwidth of

a real-time RF link.

It can also be used in multi-camera

network scenarios where digital zooming

is required but network bandwidth is

limited.

PIV modes

Two double exposure modes used for

PIV (Particle Image Velocimetry) – a fluid

mechanical measurement technique - are

implemented. The idea is to have two

separated full frame images with a short

interframing time.

After the acquisition the two images are

divided into sub-areas and cross-cor-

related, giving the direction and speed

of the flow of interest for many points

in space.

The first image is acquired

and transferred into the inter-

line registers in response to

the trigger.

The second image is stored

in the photosites and must

wait for the first image to

be read out before it can

be transferred and read

out (see fig.4). The typical

light sources for PIV are Q-

switched lasers or flashes

with short light pulses, freez-

ing most movements.

The short and well defined light pulses

make it possible to place a light pulse on

each side of the sensor gate pulse – the

strobe blanking period is 20 clk or 500

ns. The exposure time of the first image is

either fixed (mode 1) or trigger controlled

(mode 2).

1x

FOV: 2x

FOV: 3x

FOV: 4x

CCD

Object space

Image space

Figure 3: Variable Field Of View (FOV) by Sub-sampling

Fixed image format 512x512 pixels

FOV

Fixed

Lens

PIV Exposure M odes

Trigger PWC

Exposure 1

Exposure 2

1. flash

2. flash

5 µsec.

1 frame

0.5

µ

sec.

Trigger pulse width

.

1 frame

.

Trigger pulse width

Trigger pulse width

Trigger

Exposure 1

Exposure 2

1. flash

2. flash

5 µsec.

8 µsec.

1 frame

0.5

µsec.

>5 µsec.

.

.

.

Figure 4: PIV exposure modes

Layout picture

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