Introduction

The CMOS sensor module (MT9P031) incorporates the following features:

resolution to 2592 x 1944 gray scale or RGB Bayer mosaic
supports window AOI mode with faster readout
programmable analog gain (0..32dB)
progressive scan sensor (no interlaced problems!)
rolling shutter / global reset release
programmable readout timing with free capture windows and partial scan
many trigger modes (free-running, hardware-triggered)

Details of operation

The sensor uses two acquisition modes:

rolling shutter (ShutterMode = "ElectronicRollingShutter") and
global reset release shutter (ShutterMode = "GlobalResetRelease").

With the rolling shutter the lines are exposed for the same duration, but at a slightly different point in time:

Note: Moving objects together with a rolling shutter can cause a shear in moving objects.

The global reset release shutter, which is only available in triggered operation, starts the exposure of all rows simultaneously and the reset to each row is released simultaneously, too. However, the readout of the lines is equal to the readout of the rolling shutter: line by line:

Note: This means, the bottom lines of the sensor will be exposed to light longer! For this reason, this mode will only make sense, if there is no extraneous light and the flash duration is shorter or equal to the exposure time.

Furthermore, the sensor offers two operating modes:

free running mode (Overlapping exposure and readout)
snapshot mode (Sequential exposure and readout) in triggered operation

Free running mode

In free running mode, the sensor reaches its maximum frame rate. This is done by overlapping erase, exposure and readout phase. The sensor timing in free running mode is fixed, so there is no control when to start an acquisition. This mode is used with trigger mode Continuous.

To calculate the maximum frames per second (FPS_max) in free running mode you will need following formula:

FrameTime = (ImageWidth + 900) * ((ImageHeight + 9) / PixelClock)

If exposure time is lower than frame time:

FPS_max =            1
           ----------------------
                 FrameTime

If exposure time is greater than frame time:

FPS_max =            1
           ------------------------
                ExposureTime

Snapshot mode

In snapshot mode, the image acquisition process consists off several sequential phases:

Trigger

Snapshot mode starts with a trigger. This can be either a hardware or a software signal.

The following trigger modes are available:

Mode	Description
Continuous	Free running, no external trigger signal needed.
OnDemand	Image acquisition triggered by command (software trigger).
OnLowLevel	Start an exposure of a frame as long as the trigger input is below the trigger threshold .
OnHighLevel	Start an exposure of a frame as long as the trigger input is above the trigger threshold.
OnHighExpose	Each rising edge of trigger signal acquires one image, exposure time corresponds to pulse width.

See also: Using external trigger with CMOS sensors

Erase, exposure and readout

All pixels are light sensitive at the same period of time. The whole pixel core is reset simultaneously and after the exposure time all pixel values are sampled together on the storage node inside each pixel. The pixel core is read out line-by-line after exposure.

Note: Exposure and read out cycle is carry-out in serial; that causes that no exposure is possible during read out.

The step width for the exposure time is 1 us.

Image data is then shifted out line-by-line and transferred to memory.

To calculate the maximum frames per second (FPS_max) in snapshot mode you will need following formula:

FrameTime = (ImageWidth + 900) * ((ImageHeight + 9) / PixelClock)

FPS_max =                  1
           ------------------------------------
                (FrameTime + ExposureTime)

Use Cases

As mentioned before, "Global reset release" will only make sense, if a flash is used which is brighter than the ambient light. The settings in ImpactControlCenter will look like this:

In this case, DigOut0 gets a high signal as long as the exposure time (which is synchronized with the GlobalResetRelease). This signal can start a flash light.

Measured frame rates

AOI	PixelClock (MHz)	Exposure Time (us)	Maximal Frame Rate (fps)	PixelFormat
Maximum	40	100	5.9	Mono8
W:2098 x H:1574	40	100	8.4	Mono8
W:1696 x H:1272	40	100	12.0	Mono8
W:1376 x H:1032	40	100	16.9	Mono8
W:1104 x H:832	40	100	23.7	Mono8
W:800 x H:616	40	100	32	Mono8

Sensor Data

Device Structure

Progressive scan CMOS image sensor
Image size: 5.70(H)x4.28(V)mm (Type 1/2.5")
Number of effective pixels: 2592 (H) x 1944 (V)
Unit cell size: 2.2um (H) x 2.2um (V)

Characteristics

Color version

Gray scale version

Device Feature And Property List