circularity: Measure circularity of a circle in an image
In hoehleatsu/perfectcircle: Assess the Circularity of Circles via Image Aalysis

Description Usage Arguments Details Value References Examples

View source: R/perfectcircle.R

Measure circularity of a circle in an image

1	circularity(warp, seedPoints, progress, verbose = FALSE)

`warp`	The rectified image containing the circle
`seedPoints`	A `data.frame` containing the (x, y) coordinates of `type=="foreground"` and `type=="background"` pixels.
`progress`	A shiny progress bar. If `NULL` the argument is ignored. Otherwise, progress of the steps is communicated via a shiny progress bar.

Function executes the steps described in Judging Freehand Circle Drawing Competitions. Note: Opposite to the description in the blog post we assume that the image is already rectified. The steps are thus: 1. Identify the freehand circle in the image using a watershed algorithm based on seedpoint coordinates in the image. 2. Fit a perfect circle to the freehand circle using a total least squares (TLS) argument. The optimization occurs using optim. 3. Calculate the distance for each pixel on the freehand circle to the fitted perfect circle. 4. Sum of the distances.

The reported score is (1-r_{δ A})·100% where r_{Δ A} is the sum of the distances divided by the area of the fitted perfect circle, i.e. π · r².

A list containing several elements

outfile: File name (with path) of the image containing both the extracted freehand circle and the best fitting circle
outfile_intermediate: File name (with path) containing the intermediate results
area: Area of the disc made up by the freehand circle
ratio_area: Ratio between the above area and the corresponding area of the perfect circle. 1 is optimial
area_difference: Summing up all points inside and outside the perfect circle weighted by distance (see blog post for details)
score: Corresponds to (1-ratio_areadifference)*100. The optimal value is 100%.

Höhle, M. (2018), Judging Freehand Circle Drawing Competitions.

img <- imager::load.image(  system.file("extdata/", "localhost.jpg", package = "perfectcircle") )
seedPoints <- read.csv( system.file("extdata", "localhost.csv", package="perfectcircle"))
res <- perfectcircle::circularity(img, seedPoints, progress=NULL)
res

#Show the resulting file
plot(imager::load.file(res$outfile))