15
Digital Frame Grabber Information
The WEN Signal
This single is an input to the frame grabber from the camera and is
typically treated as a FTV (Field Data Valid). This signal is available on
I/O line 1. The signal can be set to trigger a grab using the
SetTriggerSource function.
Data line Options
8 bit, 10 bit, 12 bit, 14 bit, 16 bit , 32 bit –
Bits/Pixel
For a monochrome camera this describes the maximum number of
resolvable gray levels that the camera can provide. Eight bits per pixel
(256 gray levels) is quite common with 10, 12 and 14 bits/pixel available
in some models. A distinct advantage of digital camera results from
having the digital-to-analog converter moved from the frame grabber card
into the camera. This reduces the effects of transmission line noise on the
quality of the image, making the least significant bits in each pixel more
meaningful.
Modes – 8x1, 8x2 – Channel
As the resolution of the image sensor and the bits/pixel and the frame rate
increase, larger and larger amounts of image data must be transferred to
the frame grabber. To keep frame rates high many digital cameras deliver
image data via multiple (synchronized) digital outputs called channels.
Each channel is used to transfer only a portion of the image information.
For example the Dalsa CA-D4 is 1024 x 1024, 8-bit/pixel camera can
operate as either a one or two channel camera.
In order for a digital frame grabber to be able to receive more than one
pixel at a time it must first have a digital input port that is wide enough to
handle the number of simultaneous data bits the camera is transmitting. In
two-channel mode, the Dalsa CA-D4 transmits two 8-bit pixels on each
clock. A digital grabber with at least a 16-bit input port would be required.
Triggers – methods and options
A trigger signal can be set to trigger a grab using the SetTriggerSource
function. The function can also define the type of trigger event that will
cause the trigger LATCH_RISING, LATCH_FALLING,
IO_INPUT_HIGH, IO_INPUT_LOW and DEBONCE. The input lines
that can serve to trigger a grab are the Trigger line I/O line 0, WEN I/O
line 1, and GPINO input 0 line I/O line number 7. (Refer to page 241 of
the PXD Users Guide).
Debounce
Mechanical switches used as trigger inputs typically bounce, creating
spurious edges, when the contacts open or close. You will probably need
