Re: [Elphel-support] exposure sync

[Andrey Filippov]

Hello Kaien,

> "http://192.168.0.9/tuneseq.php?mode=latency"; page, i set "21 EXPOSURE 0".

is not the right place to make the changes - this page is designed to
troubleshoot latency issues and then copy the data to the C header files
with the definitions. Please follow Oleg's recommendations how to adjust
frames ahead values.

The latencies  on the tuneceq.php  page (and the data is overwritten in
memory each time you switch between TRIG=4 and TRIG=2) need to precisely
match the actual hardware latencies so the driver "knows" when to apply
changes so the particular frame (but not the one before) will be acquire
with the new parameters. Reducing those values will not make sensor to
respond to the changes faster, driver will just "think" that sensor is
faster and send the related i2c command later.

The exposure latency is rather long, especially in the sensor free-running
mode (TRIG=0) - exposure starts during the previous frame readout, when
using TRIG=4 you can save one frame, because in this mode there is no frame
exposure overlap, sensor:
1 - waits for the trigger (by default generated internally in the camera
FPGA)
2 - skips 8 scan lines (fro some internal reasons)
3 - starts exposure of the first line
4 - waits exposure time (starting exposure of lines 2,3,...)
5 - starts readout of the first line

Additionally, when using TRIG=0 mode there is additional restrictions (seems
not to be documented in the sensor datasheet) - you can not change exposure
on the next frame after it was already changed, so when implementing "HDR"
mode (alternating short/long exposures) it is possible to have odd/even
exposure change only in TRIG=4 mode. With TRIG=0 the minimal period would be
4 frames (2 - long, 2 - short)

Andrey
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Re: [Elphel-support] exposure sync

[Oleg K Dzhimiev]

Dear Kaien,

How do you change the exposure?
a) camvc ui?
b) parameters editor (parsedit)? where you need to set ProgramAhead from 3
to 0.
c) calling a function in php or C? like "elphel_set_P_arr($parsForRaw,
$thisFrameNumber)" which when called with one parameter
elphel_set_P_arr($parsForRaw) affects the 3rd frame by default. A php
example can be found in the "raw.php".

Also you can can check the exposure changing more precisely if you:
1) go to parsedit->check autoexposure and follow View/Edit
Current<%20http://192.168.0.9/parsedit.php?title=Parameters+for+groups:+autoexposure+&EXPOS&AUTOEXP_ON&AUTOEXP_EXP_MAX&AEXP_FRACPIX&AEXP_LEVEL&HDR_DUR&HDR_VEXPOS&AE_THRESH&AE_PERIOD&HIST_DIM_01&HIST_DIM_23>link.
2) mark the "Test" checkbox (if it's not there change the EXPOS parameter
for example)
3) when Test is checked - change the EXPOS once more and follow the Last
acquired 
imageslink
where you can find out to what image exactly the change had effect on
since COMPRESSOR_RUN state 0x2 (try different ProgramAhead values).

Best regards,
Oleg K Dzhimiev

On 30 September 2010 22:56, Kaien Ban  wrote:

>
> hello elphel
>
> i'm using external trigger mode.(TRIG=4)
> "http://192.168.0.9/tuneseq.php?mode=latency"; page, i set "21 EXPOSURE 0".
> When I change the exposure setting it takes three or more frames to be
> adjusted in the image.
>
> Is there a way to set the exposure for the next frame?
>
> Can you give me some advice what I should do?
>
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>
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