features op• Data kinds: image → feature
• Call: fullseye.apply(img, "cv_hough_lines", a=0.5, b=0.5) (the 2-D model is one image plus two scalar knobs a,b∈[0,1])
• HALCON equivalent: hough_lines (the HALCON reference is a useful guide to its meaning and parameters)
*The figure is the actual output on a synthetic 128×128 input. Left: input, right: output. Point clouds are drawn as a top-down scatter (brightness = z), 1-D series as a line plot, volumes as the maximum-intensity projection along z, videos as the middle frame, complex images as magnitude; return values that are not pictures are shown as the values themselves.*
Sweeping knob a (0.1 / 0.5 / 0.9, the other knob at its default):
▸ cv_hough_lines: knob a sweep (docs site)
*Knob b does not change the output (measured: identical at 0.1 / 0.5 / 0.9).*
Line (line-segment) detection via the probabilistic Hough transform (a single scalar feature, OpenCV implementation). First creates an edge image with Canny, then uses a voting scheme to find sets of edge pixels arranged in a line and detects them as segments - here, only the number of detected segments is returned (0 if none).
Corresponds to HALCON's hough_lines (Detect lines in edge images with the help of the Hough transform and returns it in HNF.) (approximation: only the number of lines, not the line parameters). The implementation is cv2.HoughLinesP(Canny(_u8(v),50,150), 1, pi/180, threshold=int(20+40*a), minLineLength=int(10+20*b), maxLineGap=5) -- a sweeps the vote threshold (minimum number of votes to accept a straight line) over 20-60, and b sweeps the minimum segment length over 10-30. Canny's internal thresholds (50, 150) and maxLineGap (5) are fixed.
• gallery2d_features family guide
• Sample-data catalog (download URLs / licences) — 2-D uses skimage.data (BSD/public domain) plus synthetic images; 3-D lists download URLs for real data sources (Stanford, PDS, …).
• Operator provenance and references — the sources of the research/methods this op family came from.
• The canonical algorithm (author, year) and its uses are named in the family usage guide above.
The program below has been verified to run (same input as the figure). In Studio's help this block becomes buttons that load and run it on the spot.
cv_hough_lines 0.50 0.50
▸ Load this pipeline · Load & run
• gallery2d_features — py -3.11 examples/gallery2d_features.py
feature as input)features)effective_bit_depth · blob_count · area_frac · count_contours · total_length · vol_count · sk_euler · sk_entropy_feat
*Provenance: ops.py — 2D operator registry. This per-op note is generated by tools/opdocs.py md (do not hand-edit).*
© 2026 Kazufumi Furuse — Fullseye operator documentation. Licensed under Apache-2.0.