regionprops

Builtin index · Images

result = regionprops(labeled) (alias of blob_stats)

Input: labeled · Output: result

What it is

labeled is a Model produced by bwlabel/label_blobs. Takes that result and returns a List of one Record per blob, in label-id order, each with fields: label (integer id), area (pixel count), centroid_x, centroid_y (real pixel-coordinate means, not bbox-center approximations), bbox_x, bbox_y, bbox_width, bbox_height (tightest axis-aligned rectangle) — all numbers.

Overloads

One call shape — this function is not overloaded.

Examples

From the documentation, and run by the build -- the output and the figure below are what the engine actually produced. Simplest first.

# Three bright discs on a dark field, written out and read back. The blob

# count printed below is then checkable against an image the reader can

# see being built, rather than asserted about a file nobody has.

n = 60
field = zeros(n, n)
centres = [15, 15; 42, 20; 30, 45]
for i in 0 to n - 1
    for j in 0 to n - 1
        for k in 0 to 2
            dy = i - centres[k, 0]
            dx = j - centres[k, 1]
            if dy * dy + dx * dx < 64
                field[i, j] = 230
            end if
        end for
    end for
end for
save_image("cells.bmp", image_from_matrix(field))

img = load_image("cells.bmp")
level = otsu_threshold(img)
mask = threshold(img, level)
clean = bwareaopen(mask, 20)          # drop specks smaller than 20 px

imshow(clean)

labeled = bwlabel(clean)
print(labeled.count)                  # number of detected blobs


stats = regionprops(labeled)
for i = 1 to labeled.count
    r = stats[i - 1]
    print(r.label, r.area, r.centroid_x, r.centroid_y)
end for

3
1 193 15 15
2 193 45 30
3 193 20 42

from images

How it works

blob_stats(labeled) (alias regionprops) — per-blob geometry from a label_blobs/bwlabel result: a Value::List of one Value::Record per blob (label, area, centroid_x, centroid_y, bbox_x, bbox_y, bbox_width, bbox_height), in label-id order. centroid_x/centroid_y are the real arithmetic mean of that blob's own pixel coordinates (not a bounding-box-center approximation); bbox_* is the tightest axis-aligned rectangle containing every one of that blob's pixels.

From the note above this builtin in the interpreter, where the reasoning was written down as it was built.