EVT 2.0 Format
EVT 2.0 is a 32-bit data format supporting sensors with up to 2048x2048 resolution. It is a very robust format that does not contain any vectorization (contrary to EVT 3.0) and is destined for low event rate applications.
The data transmission follows either little or big-endian format, which is determined by the sensor configuration. By default, IMX636 and GenX320 sensors transmit data in little-endian format, where the least significant byte comes first and the most significant one comes last.
In each 32-bit EVT 2.0 word, the 4 Most Significant Bits (MSB) are used to define the word type.
The following table depicts the different types of events data that can be encountered:
Event |
Description |
Value |
---|---|---|
CD_OFF |
OFF CD event, i.e. decrease in illumination (polarity ‘0’) |
‘0000’ |
CD_ON |
ON CD event, i.e. increase in illumination (polarity ‘1’) |
‘0001’ |
EVT_TIME_HIGH |
Timer high bits: MSB part of the events timestamp. Least Significant Bits (LSB) are attached to CD_OFF / CD_ON words. |
‘1000’ |
EXT_TRIGGER |
External trigger output |
‘1010’ |
OTHERS |
To be used for extensions in the event types |
‘1110’ |
CONTINUED |
Extra data that are used for the events which arrive in several words. Vendor specific, contact your event-based camera distributor. |
‘1111’ |
Note
Other event types are reserved. Contact your event-based camera distributor if you receive EVT 2.0 words whose type is not described in this table.
Event Time Encoding
All events are timestamped with a micro-second precision. Timestamp are encoded with 34 bits, providing a rollout after: 234 μs = 4 hours and 46 minutes. In order to minimize the amount of information stored with each event, the event timestamp is encoded in two parts. Lower 6 significant bits (0..5) of the micro-second timestamp are directly encoded into the CD or Trigger event, while the 28 most significant bits (6..33) of the timestamp are stored in a dedicated EVT_TIME_HIGH event. To rebuild the full event timestamp, the lower bits of the timestamp embedded in the event must be concatenated with the last EVT_TIME_HIGH event information.
To compute the full resolution of the timestamp, decoding of the event stream should start after receiving the first event of type EVT_TIME_HIGH.
CD_OFF
Bit Range |
Bit Width |
Field Name |
Description |
Default Value |
---|---|---|---|---|
31..28 |
4 bits |
type |
Event type | CD_OFF (‘0000’) |
(‘0000’) |
27..22 |
6 bits |
timestamp |
Least significant bits of the event time base |
– |
21..11 |
11 bits |
x |
Pixel X coordinate |
– |
10..0 |
11 bits |
y |
Pixel Y coordinate |
– |
Note
Polarity of CD_OFF events is implicitly 0, encoding a decrease of illumination.
CD_ON
Bit Range |
Bit Width |
Field Name |
Description |
Default Value |
---|---|---|---|---|
31..28 |
4 bits |
type |
Event type | CD_ON (‘0001’) |
(‘0001’) |
27..22 |
6 bits |
timestamp |
Least significant bits of the event time base |
– |
21..11 |
11 bits |
x |
Pixel X coordinate |
– |
10..0 |
11 bits |
y |
Pixel Y coordinate |
– |
Note
Polarity of CD_ON events is implicitly 1, encoding an increase of illumination.
EVT_TIME_HIGH
Bit Range |
Bit Width |
Field Name |
Description |
Default Value |
---|---|---|---|---|
31..28 |
4 bits |
type |
Event type | EVT_TIME_HIGH |
(‘1000’) |
27..0 |
28 bits |
timestamp |
Most significant bits of the event time base (33..6) |
– |
EXT_TRIGGER
Bit Range |
Bit Width |
Field Name |
Description |
Default Value |
---|---|---|---|---|
31..28 |
4 bits |
type |
Event type | EXT_TRIGGER |
(‘1010’) |
27..22 |
6 bits |
timestamp |
Least significant bits of the event time base |
– |
21..13 |
9 bits |
– |
Unused |
– |
12..8 |
5 bits |
id |
Trigger channel ID |
– |
7..1 |
7 bits |
– |
Unused |
– |
0 |
1 bit |
value |
Trigger current value (edge polarity): 0: falling edge 1: rising edge |
‘0’ |
Note
Trigger Channel ID may vary from one event-based Camera to another. Contact your event-based Camera vendor to get more information on this value.
OTHERS
Bit Range |
Bit Width |
Field Name |
Description |
Default Value |
---|---|---|---|---|
31..28 |
4 bits |
type |
Event type | OTHERS |
(‘1110’) |
27..22 |
6 bits |
timestamp |
Least significant bits of the event time base |
– |
21..17 |
5 bits |
– |
Unused |
– |
16 |
bit |
class |
Event class: 0: Monitoring 1: TBD |
– |
15..0 |
16 bits |
subtype |
Event sub-type |
– |
Note
OTHERS EVT 2.0 words are vendor specific. Contact your event-based camera vendor to get more details.
CONTINUED
Bit Range |
Bit Width |
Field Name |
Description |
Default Value |
---|---|---|---|---|
31..28 |
4 bits |
type |
Event type | CONTINUED |
(‘1111’) |
27..0 |
28 bits |
– |
Depends on the previous event |
– |
Note
CONTINUED EVT 2.0 words are vendor specific. Contact your event-based camera vendor to get more details.