op minAreaRect

Compute minimum area RotatedRect for a range of pixel intensity values in a selected image channel. This FireSight operation relies on OpenCV minAreaRect.

• min Default value is 1. Minimum pixel value to consider.
• max Default value is 255. Maximum pixel value to consider.
• channel Default value is 0. Index of BGR image channel.

Stage Model

The minAreaRect operation is actually a fast single blob detector, and provides a single RotatedRect in the model using the JSON structure expected by op drawRects. The number of points in the RotatedRect region is also given so you can compute region density.

{
  "rects":[
    {
      "x":62.514705657958984,
      "y":127.30883026123047,
      "width":43.560646057128906,
      "height":27.268278121948242,
      "angle":-59.036239624023438
    }
  ],
  "points":792
}

Example 1: Find bright green things pipeline

firesight -i img/abc-color.png -p json/minAreaRect.json -o target/minAreaRect.png -Dmin=128 -Dchannel=1 -Dthickness=1

Pixel:0.4ms RPi:11ms

Consider a colorful picture:

We can find and box all bright green things using channel=1 and min=128:

Example 2: Detect a part pipeline

firesight -i img/part1-0.png -p json/minAreaRect-thresh.json -o target/minAreaRect-thresh.png

Pixel:3.6ms RPi:150ms

Suppose we have a pick-and-place head with no part:

We then pick up a part:

Using op absdiff we get:

Starting with the absdiff'ed image, the pipeline uses op threshold to generate this image with Otsu's method:

Finally, the minAreaRect stage itself gives us: