Detail energy · % of open baseline
Methods & notes
Detail energy
Subtract a softly filtered image from the original, then average the squared difference to measure fine-detail contrast.
E = mean[(L − G₀.₈ ∗ L)²]
Energy (%) = 100 E / E₀
L: linear image brightness. G₀.₈ ∗ L: brightness smoothed by a Gaussian filter (σ = 0.8 px). E₀: unblurred, fully open energy.
The average covers the visible moving panel, excluding a 3 px edge margin. Treatment uses the transition's paper blur (growing with the sheet's distance from its image, with darkening that follows it) at the selected scattering strength.
Optical flow
Match image patches between two rendered frames, then average their displacement to estimate content motion.
d = argminᵤ Σq∈P [A(q) − B(q + u)]²
Motion = mean(‖d‖)
A, B: rendered brightness frames 2° apart. P: sampled image patch; q: a pixel in it. u: candidate pixel offset. d: best-matching offset; ‖d‖: its length. Motion is in pixels per 2° of folding.
Only reliable, visible moving-panel matches count; fewer than four produces a gap. Arrows exaggerate displacement ×5, capped at 34 px.
Fixed camera, 512 × 512 px. Graphs use 6° samples, a 1:2:1 smoothing filter, and interpolation. These metrics do not establish visual comfort.