An EPICS areaDetector plugin to perform edge detection using the OpenCV Canny function.
Additional information:
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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.
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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 |
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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.