...And Calculating Bandwidth


The PL-B780, PL-B740, and board level equivalents use a 40 MHz pixel clock to read out pixel data at 25 nanoseconds per pixel.  Each PL-B780 row has a delay of 7.3 microseconds and is padded with 10 isolation pixels, while each PL-B740 row has a delay of 3.55 us and is also padded with 10 isolation pixels.  If the camera is operating in 16-bit mode or YUV mode, the number of padded pixels becomes twice the ROI number of columns.  The row readout times, are given by:


PL-B780 8-bit mode RowReadoutTime = 7.3 us + 25 ns x (Npixels + 10)


PL-B780 16-bit mode/YUV RowReadoutTime = 7.3 us + 25 ns x (Npixels x 2)


PL-B740 8-bit mode RowReadoutTime = 3.5 us + 25 ns x (Npixels + 10)


PL-B740 16-bit mode/YUV RowReadoutTime = 3.5 us + 25 ns x (Npixels x 2)


where Npixels is the number of active pixels in the row.  


The PL-B770 cameras are similar with a 48 MHz pixel clock to readout data at 21 nanoseconds per pixel.  The PL-B774 row has a delay of 6.7 microseconds and is padded with 2 isolation pixels, while the PL-B776 row has a delay of 7.7 us and is padded with 21 isolation pixels.  The PL-B774 also has 15 rows added to the region of interest and the PL-A776 has 4 rows added.  If the camera is operating in 16-bit mode or YUV mode, the number of padded pixels becomes twice the ROI number of columns.  The row readout times, are given by:


PL-B774 8-bit mode RowReadoutTime = 7.3 us + 21 ns x (Npixels + 2)


PL-B774 16-bit mode/YUV RowReadoutTime = 7.3 us + 21 ns x (Npixels x 2)


PL-B776 8-bit mode RowReadoutTime = 6.7 us + 21 ns x (Npixels + 21)


PL-B776 16-bit mode/YUV RowReadoutTime = 6.7 us + 21 ns x (Npixels x 2)

 


For example, for the full ROI on the PL-B782, the row readout time is 7.3 + 25 x (2208+10) / 1000 = 62.75 µsec/row.


For Rolling Shutter operation with very short exposures, the minimum frame interval can be calculated by multiplying the minimum row readout time by the number of rows in the image.  


Example

For example, with a 1200 x 960 ROI and decimated by 2, the output image is 600 x 480.  


This ROI is readout once every 480*(7.3 +25*600/1000)/1000 = 10.7 milliseconds or at a maximum frame rate of 93.4 frames per second.  


In this example, the maximum frame rate is valid for exposures of 10.7 milliseconds or less.  For exposures greater than 10.7 milliseconds, the frame rate is a function of the exposure time.


For Fast Reset Shutter operation, the minimum frame interval can be found by adding together the row reset time of 3.55 µsec/row, the integration time and the minimum row readout time.  Note that during Fast Reset Shutter, the row delay decreases from 7.3 us to 3.55 us.


Example


Assume a 2 millisecond exposure time and output image ROI of 600 x 480.


480 x (3.55 us + 25 ns x 600) = 8.90 ms.

Therefore the minimum frame interval is 8.90 ms + 2 ms + 3.55 us x 480 = 12.60 ms which gives 79.4 frames per second.


The above calculations determine the maximum frame rates possible.  The actual frame rates achieved depend on the camera’s bandwidth controls, other traffic on the FireWire bus, and the resources available on the host computer.  Use the frame rate calculator, located on our web site under the product downloads, to determine the maximum frame rate a camera can achieve for given parameters.