[Elphel-support] rolling shutter or global shutter

[support-list]

Dear Servaas,

it is easy to get confused with Aptina documentation :-)

First of all - three sensors: MT9P001, MT9P031 and MT9P006 seem to have the same chip, differences are in intended market and microlens/filter array. When reading chip ID - the value is exactly the same for all 3 devices - 0x1801.

"Global reset release" in Aptina documentation means that in this mode reset is removed simultaneously from all the rows, but exposure is from the end of reset to the readout of the same line, so it this mode exposure of the last line is 1/15 sec longer than the exposure of the first line. This mode can be useful in 2 cases:
1 - scene is totally dark, so pixels are only exposed by the flash, no background illumination
2 - you have additional mechanical shutter to end exposure

In ERS mode both reset and readout are rolling, so exposure of each line is constant.

In addition to a free-running ERS mode we also use "snapshot" ERS (it is called so in Aptina docs, but it is not what people mean by snapshot shutter). In this mode rest of the sensor lines start after external trigger, readout starts exposure_time later, so exposure sweeps over the sensor once, starting at known time. We use this mode in all multisensor applications (such as Eyesis4pi) to provide precise synchronization between the channels.

We did not use the GRR mode, but it is rather easy to implement by overwriting the value of the sensor register 0x1e, setting bit 7 to "1" after the trigger mode is programmed. When the camera is triggered from the internal FPGA trigger (not from the external input) the programmable  trigger delay applies to output pulse that can be used for the flash. If you plan to use external trigger for the camera, you may just use it to trigger the flash also. In the GRR mode (that will require register overwrite after setting TRIG=4 http://wiki.elphel.com/index.php?title=Trigger ) programmed exposure will mean the shortest exposure (exposure of the first line), it should be set to be longer than the flash duration.

Alternatively you may use flash without synchronization in plain ERS mode with the exposure set to full frame duration and than add two consecutive frames that captured the flash.

Andrey  



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