Theory of operation
Video Pipeline
A video signal contains all the pixels for every frame. The resolution determines the amount of pixels: for example,
1920 x 1080 means 1920*1080 pixels on your screen. Each of these pixels contains the color information it will show on
screen.
Colors are described using the RGB (Red-Green-Blue) format. For every video frame, each pixel has access to 24 bits of
color information (8 bits per color). This means, for example, that red can take values from 0 to 255 and consequently
that 256 different shades of red are possible. Red 0 signifies no red, while red 255 signifies 100% red color. All of the
three colors (RGB) have 8 bits, which creates 16 777 216 different possible colors. RGB colors are usually represented as
(R,G,B), where R, G and B are the respective color values [0-255].
A color is usually described with 8 bits of information. 8-bit information can be seen as R
7
R
6
R
5
R
4
R
3
R
2
R
1
R
0
, which is a
binary representation of the color (in this example, R for Red). Every bit (R
i
) can take the value 0 or 1, and the final
value will be a sum:
=
2
The color red 255 would be represented as 0b11111111, whereas red 16 would be 0b00010000. Since 255 represents
every bit at a value of 1, it is the maximum value for an 8-bit number.
Video and I/O synchronization
The PROPixx displays video information with no processing delay, and the I/O subsystems have microsecond-precise
synchronization with the incoming video vertical sync pulse. The system waits until it has received a complete video
frame, then presents all raster lines simultaneously (rather than being scanned from top to bottom) starting at about t =
8.33 ms in the case of a 120 Hz video refresh rate. In the case of 480 Hz stimulation, this fixed latency would drop to
about 2.08 ms.
DVI Out
A second display can be connected to the DVI Out port. This secondary display can be used, for example, by a remote
operator who wishes to monitor the stimuli being presented to a test subject.
Analog output interface
The PROPixx analog subsystem contains 4 DAC (Digital-to-Analog-Converter) channels, with 16-bit precision and ±10 V
output swing. The maximum update rate is 1 MSPS and all 4 channels update simultaneously. The DAC update rate can
be specified in samples per second, samples per video frame, or nanoseconds per sample. Waveform onset can be
synchronized to video refresh with microsecond precision.
Copyright © 2015 VPixx Technologies Inc. All Rights Reserved
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