SHARPENING was the doc's §4.2 kernel with the two parts of §4.2 missing from
it. `CLARITY_SKSL` evaluated the 3x3 unsharp mask with Mask = 1 on every pixel
and no coring at all, so a flat sky, a cheek and a noise speckle all took the
gain an eyelash took. That is `thay_doi_thong_so_giong_lightroom.md` §1 written
out as a bug: "khi Sharpen, ảnh nổi đầy sạn hạt cát" — the knob could not raise
the contrast of an edge without raising the noise of everything beside it, and
on a grainy frame the second effect won.
`SHARPEN_SKSL` is the doc's own line, `Image + Amount x HighPass x Mask`, with
the two terms it names:
- EDGE DETECTION: the Sobel magnitude G = sqrt(Gx^2 + Gy^2) on luminance, put
through the doc's soft threshold smoothstep(T, T + 0.1, G). Flat fields
read G = 0 and get Mask = 0 — the pixel is handed back untouched.
- DETAIL (halo coring): a high-pass under SHARPEN_CORE is a speckle, not a
detail, and is suppressed. The coring is soft (a ramp across the threshold,
not a cliff) so a detail sitting on it is not switched on and off from one
pixel to the next.
The HIGH-PASS is the doc's Radius, held at one image pixel — 0.7-0.9px on a
Retina panel — and it is a LUMINANCE high-pass carried by all three channels.
A per-channel kernel sharpens a red edge against a green one and draws a colour
fringe down every contour; the file's own §3 rule is to keep R/L, G/L and B/L
where they were.
`scripts/sharpen-check.mjs` pins the three properties the old kernel could not
have: a flat field and a field of grain come back unchanged, a step below the
threshold comes back unchanged, and a hard step moves apart on both sides while
the flat halves beside it stay put. `CLARITY_SKSL` and `clarityUniforms` are
gone with it, and the header note that said CanvasKit had two convolution steps
to replace now says the one it has.
Checked: node scripts/sharpen-check.mjs; node scripts/denoise-check.mjs; node
scripts/tone-base-check.mjs; node scripts/highlight-knee-check.mjs; node
scripts/auto-tone-check.mjs; node scripts/half-check.mjs; node
scripts/mask-wb-check.mjs; node scripts/preview-match-check.mjs; node
scripts/raw-develop-check.mjs; node scripts/white-level-check.mjs; node
scripts/wb-table-check.mjs; npx tsc --noEmit.
