ADPluginEdge

An EPICS areaDetector plugin to perform edge detection using the OpenCV Canny function.

Additional information:

• Documentation.

  This routine finds edges in an image using the Canny algorithm (John Canny. A computational approach to edge detection. Pattern Analysis and Machine Intelligence, IEEE Transactions on, (6):679–698, 1986.) The routine is cool if for no other reason than that the primary source shows an image of a Dalek before and after edge detection.

  There are two parameters: "LowThreshold" and "ThresholdRatio". Use the low threshold to adjust the sensitivity. Canny suggests that the threshold ratio be "two or three to one".

  To make use of this detector a vertical line is taken midway between the left and right edges of the image. The first edge from the top (TopPixel) and the first edge from the bottom (BottomPixel) are found TopEdgeFound and BottomEdgeFound. If the top and bottom edges are different then "VerticalFound" is set true.

  Likewise, a horizontal line is drawn midway between the top and bottom edges of the image.

• Input PVs

PV	Comment
LowThreshold	Lower values increase the sensitivity of the detector
ThresholdRatio	Sets the size of the hysteresis of the edge detector (2 to 3 are reasonable)

• Output PVs

PV	Comment
BottomEdgeFound	Indicates that a bottom edge was found (0 = 0, 1 = Yes)
BottomPixel	Location of the first edge from the bottom measured in pixels from the top edge
HorizontalCenter	Average of the LeftPixel and RightPixel
HorizontalFound	Indicates that both a left pixel and a right pixel were found and they are not the same
HorizontalSize	Difference between RightPixel and LeftPixel
LeftEdgeFound	Indicates that a left edge was found (0 = No, 1 = Yes)
LeftPixel	Location of the first edge from the left measured in pixels from the left edge
LowThreshold_RBV	Read back value for LowThreshold
RightEdgeFound	Indicates that a right edge was found (0 = No, 1 = Yes)
RightPixel	Location of the first edge from the right measured in pixels from the left edge
ThresholdRatio_RBV	Read back value for ThresholdRatio
TopEdgeFound	Indicates that a top edge was found (0 = No, 1 = Yes)
TopPixel	Location of the first edge from the top measured in pixels from the top edge
VerticalCenter	Average of TopPixel and BottomPixel
VerticalFound	Indicates that both a top pixel and a bottom pixel were found and they are not the same
VerticalSize	Difference between BottomPixel and TopPixel

• Release notes.

  For this implementation the image must be 8 bit monochromatic. Fortunately there are some other plugins (ColorConvert and Process) that allow you to convert to this format.

  There is a plethora of other functions in openCV that would likely be useful as areaDetector plugins.

  Needless to say, you'll need to install opencv (http://opencv.org). This code was built using verion 3.0 of the opencv API.