Glossary#

Aligned frame — A frame after registration: warped onto frame 0's pixel grid, brightness equalized, ready to be compared pixel to pixel with the others.

Alignment model — How much a frame may be deformed to land on the previous one. Similarity is shift, scale and rotation; affine adds aspect and shear; projective adds perspective. See alignment.

Band-pass level — One level of a Laplacian pyramid: the detail that exists at one scale and not the next.

Batch — Several stacks run in turn from one command or one session, cut out of a long frame list by a splitting rule.

Coarsen — --align-coarsen N: stop the registration search N levels short of full resolution. A large speed-up at sub-pixel accuracy, because the transform is resolution-independent.

Confidence map — How much the depth pass trusted each pixel's own focus measurement, normalized so its 90th percentile is 1. Dark areas were filled in from neighbors.

Content credentials — C2PA provenance metadata embedded in a saved file, recording that lapstack made it and how. See saving.

Depth from focus (DFF) — Recovering a depth map from which frame each point came into focus in. See depth from focus.

Depth map — The fractional frame index at which each pixel came into focus. A measure of relative distance, in units of frame index.

DFR — depth-map rendering — A second stacked image rendered from the depth map: each pixel is the average of the one or two frames nearest its depth. See other renderings.

Draft — --draft N: run everything at 1/2^N the size, for checking settings quickly.

Dust map — A frame of an evenly lit blank surface shot out of focus, used to find and remove sensor dust from every frame before alignment. See dust map.

Focus bracketing — Taking a series of photographs with the plane of focus stepped between them. The camera-driven alternative to a focusing rail.

Focus measure — A per-pixel number saying how sharp the neighborhood is. lapstack's default is the ring difference filter.

Focus peaking — A magenta band painted over the pixels a frame has in focus, swept as you scrub. The check to run before trusting a stack.

Focus slice — One frame's focus measure on the depth pass's working grid, kept as the frame is folded. The one thing that grows with a stack's length.

Fold — Adding one frame into the running fused pyramid. lapstack folds frames in one at a time, which is why memory does not grow with the stack.

Gaussian pyramid — A sequence of progressively smaller, blurrier copies of an image.

Guide level — The pyramid level whose region energy drives halo control, and the level the winner map is read from. --depth-level, default 2.

Halo — A soft rim beside a bright or dark object, left by each pyramid level picking its own winner. See halo control.

In focus — A viewer layer showing one frame's own pixels with everything the result did not take from it dimmed away. Helicon's "source map".

Kept result — A result held on past its own run, so it can be compared, brushed from, or saved later. See project files.

LAP — lapstack's main output: the Laplacian-pyramid fusion.

Laplacian pyramid — The differences between consecutive Gaussian pyramid levels, plus a small residual. Complete, linear, and the structure the whole fusion is built on.

Linear DNG — A DNG written in the camera's own linear color space, so a raw converter develops the stacked image like a raw. See saving.

Near end — Which end of the stack frame 0 is. Decides who wins where surfaces overlap in the stereo, rocking and 3D outputs. Get it wrong and the relief looks inside out.

Pareto rule — lapstack's generalization of the paper's two-frame residual rule to N frames: a frame is dominated if another is at least as good on both measures and better on one, and the fused value is the mean of the non-dominated frames.

Peaking — See focus peaking.

Project file — A .lapstack.json holding a session's frames, settings, registration and retouch strokes. Not the images. See project files.

REDUCE / EXPAND — The two pyramid operations: blur and downsample, upsample and blur.

Refold — Making a stereo or rocking view by fusing the whole stack again with every frame shifted sideways by its index — Zerene's method — instead of shearing the result by its depth map.

Region energy — The sum of squared pyramid coefficients over a small weighted window. The measure the fusion picks winners by.

Registration — Finding the transform that brings one frame onto another. See alignment.

Residual — The small low-pass image at the bottom of a Laplacian pyramid, carrying the overall tone and color.

Retouch — Painting one rendering into another by hand, from a source frame, a slab, another stacked result or a kept result. See retouching.

Ring difference filter (RDF) — lapstack's default focus measure: the absolute difference between the mean of a small disk and the mean of a ring around it. From Jeon et al., 2019.

Shear — Making a side view by sliding every pixel sideways in proportion to its depth. The alternative to a refold, and much cheaper.

Slab — A run of consecutive frames fused on its own. A thick plane of focus, used as a retouch source and as a rendering mode. Zerene's term.

Splitting rule — How a batch cuts a frame list into stacks: by count, by pause in the capture times, or by folder.

Stack — A focus-bracketed series of photographs of one subject; also, what lapstack makes from one.

WAV — weighted average — A stacked image in which every frame is averaged with a weight following its local contrast, so nothing is ever picked outright. Helicon's method A. Softer than LAP, with no seams or halos.

Winner map — Which frame won at a given pyramid level. A by-product of the fusion, useful for debugging it and noisy wherever the scene is flat — not a depth estimate.

WLS — weighted least squares — The edge-aware smoothing that turns noisy per-pixel focus peaks into a coherent depth map, weighted by confidence so measured pixels dominate inferred ones.

Working grid — The reduced resolution the depth pass runs at, set by --depth-scale (default 1, meaning half resolution).