Pair presets
Presets configure the
top
and
bottom
figures together for classic, extreme, neutral and explanatory conditions.
Global
Canvas margin (px)
80
Line colour
Black
Blue
Magenta
Teal
Background stripes (assimilation)
None
Parallel to shafts
Orthogonal to shafts
Stripes contrast
20%
Underlay (Gregory perspective test)
Underlay type
None
Inside room corner
Outside building corner
Underlay strength (opacity)
40%
Perspective (vanishing) amount
60%
Swap between an
inside corner
and an
outside (building) corner
to see whether 3‑D interpretation modulates the illusion for you, as proposed by Richard Gregory.
Top figure
Configuration
Wings‑in (arrowheads)
Wings‑out (tails)
T‑caps (90°)
Circular end‑caps
No ends (plain line)
Feathered (multiple fins)
Shaft length (px)
420
Shaft thickness (px)
4
Wing angle (°)
45°
Wing length (px)
60
Wing thickness (px)
3
Feather fins (count)
4
Feather spacing (px)
12
Bottom figure
Configuration
Wings‑out (tails)
Wings‑in (arrowheads)
T‑caps (90°)
Circular end‑caps
No ends (plain line)
Feathered (multiple fins)
Shaft length (px)
420
Shaft thickness (px)
4
Wing angle (°)
135°
Wing length (px)
60
Wing thickness (px)
3
Feather fins (count)
4
Feather spacing (px)
12
Psychophysics mode
Lock lengths equal
Length offset (top − bottom, px)
0
Set
Lock lengths
on, then adjust
Length offset
until the two lines
look
equal to you: that difference is your approximate
PSE
(point of subjective equality).
Overlays & export
Show measuring ticks
Show central bisection marks
Export PNG
Export SVG
Reset
Illusion strength (heuristic)
—