added aspect ratio formula to 'measure_shapes_act1.md'

_includes/measure_shapes/measure_shapes_act1.md

@@ -2,16 +2,17 @@
 
 - Using a drawing board discuss some shape features and concepts, e.g.,
   - Area
-  - Perimeter: Like all surface measurements, this is tricky, e.g., 
+  - Perimeter: Like all surface measurements, this is tricky, e.g.,
     - Counting the number of perimeter pixels approximates the bounding box
     - See the famous [england's coastline paradox](https://en.wikipedia.org/wiki/Coastline_paradox)
   - Circularity = ( 4 * Pi * Area ) / Perimeter^2: Designed to be 1.0 for a perfect circle
+  - Aspect ratio: Major ellipse axis length / Minor ellipse axis length
   - Solidity = Convexity = Area / Convex_hull_area: Useful to find objects with spikes or indentations
   - Ellipse fit parameters or Elongation: Useful to measure object elongation
   - Discuss issues with small object in digital images, e.g., by exploring a square (=circle?!) of 2x2 pixels.
 - Open an image with objects, e.g.,
   - Fluorescence image with nuclei of different shapes: [xy_16bit_calibrated__nuclei_various_shapes.tif](https://github.com/NEUBIAS/training-resources/raw/master/image_data/xy_16bit_calibrated__nuclei_various_shapes.tif)
   - Label image with objects of different shapes: [xy_8bit_labels__four_objects.tif](https://github.com/NEUBIAS/training-resources/raw/master/image_data/xy_8bit_labels__four_objects.tif)
-  - Label image with circles of different sizes: [xy_8bit_labels__circles_different_size.tif](https://github.com/NEUBIAS/training-resources/raw/master/image_data/xy_8bit_labels__circles_different_size.tif) 
+  - Label image with circles of different sizes: [xy_8bit_labels__circles_different_size.tif](https://github.com/NEUBIAS/training-resources/raw/master/image_data/xy_8bit_labels__circles_different_size.tif)
 - Perform shape features such as area, perimeter, circularity, and solidity
 - Discuss how objects can be distiguished by various shape measurements