Video capturing circuit works with clock restoration
based upon the VCXO phase locking loop (PLL). This
causes high stability of the restored sampling clock
and, in consequence high quality of the captured image.
VCXO-based restoration circuit is recommended in high-
resolution video systems, where slight changes in the
phase clock can disturb the captured image
smoothness. The circuit is equipped by automatic
black-level detection (CLAMP), what makes it possible
to process images correctly for different images with
contents. A/D conversion is always performed for the
active part of the line, and the black level of the signal
is assigned to a certain quantization value.
The possibility of reprogramming of the graphical
processor during its operation is the additional feature
of the presented solution. Both the image memory and
GSP's registers are accessible for Host in any time. The
local software running on GSP platform has been
written with the use of „C” and assembly language for
Texas Instruments graphic processors.
1-4 «e E:
Chanel |<«— | Four
i Video
Video(CCIR) |«— |
Multiplexer j<— | "Puts
Synchro H sync base V
ey signals oe om vexb
separation \V sync
Clamp H synop
—>| ADC VCLK
RAS
CAS AT bus
8 | Data DTOE Phase
SCLK | comparator
WR
m" ^ 16 | Buffer 16
TMS44c251 7 E À vicit
Host Bus
sae i
7
Local video bus
Figure 1. Frame grabber block diagram
Additionally, the presented solution is uses the
clamping circuitry for proper A/D conversion being
independent from the contents of the image. The entire
interface has been designed with the use of
programmable logic devices (PLDs) in the form of half-
size IBM PC-compatible computer-card.- In order to
fasten the transmission and capturing rate, 8/16-bit
DMA transfer is applied. This feature allows to use the
presented interface in so-called "Life-video" mode,
where the moving images are being displayed on the
computer screen in real-time. A small size of developed
interface makes it possible to use it in the portable
Notebook Computer.
The presented frame grabber card for this system has
been made at the Institute of Electronics, Technical
University of Lodz. It has maximum 4 video analog
inputs for independent, parallel connection of 4 CCD
Panasonic cameras, which are compatible with
514
monochrome television video signal in CCIR standard
(25 full images/ sec.). The frame grabber uses the
composite video signal for digitization. The frame
grabber enables conversion of successive video
sequences generated by the CCD cameras from analog
to digital form, and further transmission to the
operational memory of a computer. Theoretical
dimensions of the image recorded by the frame grabber
before digitization amounts to 7.1(H) x 4.0(V) mm?
while dimensions of scene after frame grabbing
amounts to 5.3(H) x4.0(V) mm? respectively. Thanks
to high frequency of pixel digitization (ca 15 MHz)
pixels are approximately squares of 8.3 pum in size.
Ratio of the pixel sides lengths amounted to 1.007.
Others basic technical parameters of the designed
frame grabber board :
e frame size HxV 640x480
e number of digitized discrete grey levels 256
e number of grey levels (VGA) 64
e converter A/D and D/A
©
®
8 bit
file size with single image 307 kB
max. number of images displayed
at the same time 4
e max. number of measuring points
on the image 100
The frame grabber card has been installed to the PC
5P60 computer it means Pentium with PCI-GOMHz
board, 16 MB Ram, that was equipped with 64-bits
graphic accelerator SVGA, PCI Matrox II of 2MB
memory. Video is displayed on a 17" RGB monitor
manufactured by MAG Technology. For assurance of
correct and optimal work of the system, it is important
to use the SVGA graphic card configured to have
resolution of 800 x 600 and to display at least 256
colours. If the conditions are not fulfilled, the images
will be displayed in pseudo-colours, instead of proper
grey levels.
3.3 Control and manages software
The software that controls and manages the frame
grabber has been written in the Borland C++
programming language as application under MS
WINDOWS 3.1 environment and is steered by user
through a system of menu and submenu. The software
allows to capture the images as well as to process
them. The implemented procedures enable image
acquisition, processing enabling geometric
transformations of digital images and interactive
measurement of pixel coordinates. Processing is carried
out in off-line mode, after storing the images in
computer memory.
The basic menu of the programme consists of the
following options : File, Edit, View, Options, Camera,
Window, About. In case of choosen orders it is possible
to call the option in fast mode through pressing proper
buttons of the keyboard (e.g. zoom through F10). If
certain option cannot be used because of false using of
the program that controls the work of the frame
grabber, then the respective option is displayed in grey.
Some examples of windows displayed the digital
images are shown in the Figure 2.
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B5. Vienna 1996
Figure 2
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