Multiple exposures in one frame¶

Multiple exposures in one frame

The multiple exposure feature effectively accumulates several exposures into a single frame.

At the end of each exposure, the pixel values are transferred to a pixel buffer, and the sensor starts again from zero.
The readout of the frame starts after the last exposure period has finished.
Once the required number of exposures is completed, the resulting output frame is the sum of all exposures for each pixel.
As you can see in the text below, this feature can work in two modes - either with defined bursts or controlled by the duration of the trigger pulse.

The number of exposures can be defined using the XiApi parameter XI_PRM_EXPOSURE_BURST_COUNT.

According to Sony, the maximum number of exposures per frame is 4095.
However, please note that there is a gap between each exposure, which could be ~50-150µs depending on the sensor.

Camera models supported¶

Some of the XIMEA cameras support multiple exposures captured in a single frame.
The models supporting this feature are based on Sony Pregius sensors like:

IMX252, IMX250, IMX255, IMX253

Camera models with these sensors can be found in the following camera families:

xiC camera family
xiX camera family

Sensor model	Camera model	Chroma	Interface
Sony IMX252	MC031MG-SY	Monochrome	USB3
Sony IMX252	MC031CG-SY	Color	USB3
Sony IMX252	MX031MG-SY-X2G2	Monochrome	PCIe Gen2 x2
Sony IMX252	MX031CG-SY-X2G2	Color	PCIe Gen2 x2
Sony IMX250	MC050MG-SY	Monochrome	USB3
Sony IMX250	MC050CG-SY	Color	USB3
Sony IMX250	MX050MG-SY-X2G2	Monochrome	PCIe Gen2 x2
Sony IMX250	MX050CG-SY-X2G2	Color	PCIe Gen2 x2
Sony IMX255	MC089MG-SY	Monochrome	USB3
Sony IMX255	MC089CG-SY	Color	USB3
Sony IMX255	MX089MG-SY-X2G2	Monochrome	PCIe Gen2 x2
Sony IMX255	MX089CG-SY-X2G2	Color	PCIe Gen2 x2
Sony IMX253	MC124MG-SY	Monochrome	USB3
Sony IMX253	MC124CG-SY	Color	USB3
Sony IMX253	MX124MG-SY-X2G2	Monochrome	PCIe Gen2 x2
Sony IMX253	MX124CG-SY-X2G2	Color	PCIe Gen2 x2

Note: This feature can also be implemented (currently is NOT) in cameras based on Sony Pregius S sensors, like:
IMX547, IMX546, IMX545, IMX542, IMX541, IMX540, IMX537, IMX536, IMX535, IMX532, IMX531, IMX530

Applications¶

A typical application is tracking a light spot in the dark, where the resulting image captures the trajectory of the point over time.

Exposure defined by XiApi parameter "XI_PRM_EXPOSURE"¶

In this mode, the trigger defines the start of the exposure, but the length of the exposure is defined by the XI_PRM_EXPOSURE xiApi parameter. Set exposure length using XI_PRM_EXPOSURE parameter and set XI_PRM_TRG_SELECTOR to XI_TRG_SEL_EXPOSURE_START.

// Set exposure
xiSetParamInt(xiH, XI_PRM_EXPOSURE, 1000);
// Set the number of times of exposure in one frame
xiSetParamInt(xiH, XI_PRM_EXPOSURE_BURST_COUNT, 5);
// Set trigger selector
xiSetParamInt(xiH, XI_PRM_TRG_SELECTOR, XI_TRG_SEL_EXPOSURE_START);

Exposure defined by the length of the trigger pulse¶

In this mode, both the start of the exposure as well as the length of the exposure is defined by the trigger pulse. Set XI_PRM_TRG_SELECTOR to XI_TRG_SEL_EXPOSURE_ACTIVE. The exposure length will be defined by the trigger pulse length.

// Set the number of times of exposure in one frame
xiSetParamInt(xiH, XI_PRM_EXPOSURE_BURST_COUNT, 5);
// Set trigger selector
xiSetParamInt(xiH, XI_PRM_TRG_SELECTOR, XI_TRG_SEL_EXPOSURE_ACTIVE);

Note: In both of the above modes, there is a short period (FOT) after each exposure during which time the next exposure cannot start. In the case of the cameras with IMX sensors, this period is 11*line_period (the line_period depends on various other parameters, see Line Period in the Camera performance calculator).

Note2: None of the above two modes support the start of exposure during readout (trigger overlap feature).

Note3: Limitations of the IMX sensors in multi-exposure mode lead to an increase in noise in comparison to a single exposure frame.

Note4: The multi exposure mode does not work ideally when ultra short exposure times are used (<15us).