January 30, 2018

Photo Finish

by Oleg Dzhimiev

Photo Finish: all cars driving in the same direction effect

Since 2005 and the older 333 model, Elphel cameras have a Photo Finish mode. First, it was ported to 353 generation, and then from 353 to 393 camera systems.

In this mode the camera samples scan lines and delivers composite images as video frames. Due to the Bayer pattern of the sensor the minimal sample height is 2 lines. The max fps for the minimal sample height is 2300 line pairs per second. The max width of a composite frame can be up to 16384px (is determined by WOI_HEIGHT). A sequence of these frames can be simply joined together without any missing scan lines.

Current firmware (20180130) includes a photo finish demo: http://<camera_ip>/photofinish

A couple notes for 393 photo finish implementation:

  • works in JP4 format (COLOR=5). Because in this format demosaicing is not done it does not require extra scan lines, which simplified fpga’s logic.
  • fps is controlled:
    • by exposure for the sensor in the freerun mode (TRIG=0, delivers max fps possible)
    • by external or internal trigger period for the sensor in the snapshot mode (TRIG=4, a bit lower fps than in freerun)

See our wiki’s Photo-finish article for instructions and examples.


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