Image > Trap (CMYK prepress trapping)
Clean-room trap: per-ink grayscale dilation (separable max filter, par_rows/wasm-safe) applied only under already-inked pixels, so internal colour edges get a trap band while object-vs-paper edges stay clean. Engine image.trap (CMYK-only, active pixel layer, one history step). algo 3 tests + engine 2 tests. Parity 607 -> 608; FLOOR 603. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Brandon Thomas
parent
61aa2f9748
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@ -44,6 +44,7 @@ pub mod matting;
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pub mod quantize;
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pub mod stack;
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pub mod tone;
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pub mod trap;
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pub mod transform;
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pub mod warp;
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pub mod liquify;
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@ -0,0 +1,125 @@
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//! Image › Trap (prepress). Trapping spreads each ink slightly into neighbouring inked areas so
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//! that, if the press misregisters the plates, the colours still overlap at an edge instead of
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//! leaving a white gap. We spread every ink by `width` px (grayscale dilation) but only *under*
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//! already-inked pixels, so internal colour edges get a trap band while the object-vs-paper edge is
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//! left alone. Clean-room approximation of Photoshop's Trap, which works on a flattened CMYK image.
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//!
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//! Operates on an interleaved buffer of `ch` channels per pixel (CMYK = inks 0..4, plus alpha).
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use crate::photo_util::par_rows;
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/// Separable grayscale dilation (max filter) of one interleaved channel, radius `r` px.
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fn dilate_channel(src: &[f32], w: usize, h: usize, ch: usize, c: usize, r: usize) -> Vec<f32> {
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let get = |buf: &[f32], x: usize, y: usize| buf[(y * w + x) * ch + c];
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// Horizontal pass.
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let mut tmp = vec![0.0f32; w * h];
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par_rows(&mut tmp, w, 1, |y, row| {
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for (x, o) in row.iter_mut().enumerate() {
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let lo = x.saturating_sub(r);
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let hi = (x + r).min(w - 1);
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let mut m = 0.0f32;
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for xx in lo..=hi {
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m = m.max(get(src, xx, y));
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}
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*o = m;
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}
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});
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// Vertical pass over tmp.
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let mut out = vec![0.0f32; w * h];
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par_rows(&mut out, w, 1, |y, row| {
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let lo = y.saturating_sub(r);
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let hi = (y + r).min(h - 1);
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for (x, o) in row.iter_mut().enumerate() {
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let mut m = 0.0f32;
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for yy in lo..=hi {
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m = m.max(tmp[yy * w + x]);
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}
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*o = m;
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}
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});
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out
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}
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/// Trap an interleaved CMYK(+alpha) buffer in place. `width` is the trap in px (>=1). Inks 0..4 are
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/// spread; any alpha channel (`ch > 4`) is untouched. A pixel keeps its original ink where it has
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/// no ink at all (paper), so only internal colour edges gain a trap band.
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pub fn trap(px: &mut [f32], w: usize, h: usize, ch: usize, width: usize) {
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if width == 0 || w == 0 || h == 0 || ch < 4 {
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return;
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}
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let inks = 4.min(ch);
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let dil: Vec<Vec<f32>> = (0..inks).map(|c| dilate_channel(px, w, h, ch, c, width)).collect();
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par_rows(px, w, ch, |y, row| {
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for (x, pixel) in row.chunks_exact_mut(ch).enumerate() {
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let i = y * w + x;
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// Printed where any ink is present.
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let inked = (0..inks).any(|c| pixel[c] > 1e-4);
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if !inked {
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continue;
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}
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for c in 0..inks {
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pixel[c] = pixel[c].max(dil[c][i]);
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}
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}
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});
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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/// Two solid ink blocks meeting at x=4: cyan (C) on the left, magenta (M) on the right.
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fn two_blocks() -> (Vec<f32>, usize, usize) {
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let (w, h, ch) = (8usize, 4usize, 4usize);
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let mut px = vec![0.0f32; w * h * ch];
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for y in 0..h {
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for x in 0..w {
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let p = &mut px[(y * w + x) * ch..][..ch];
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if x < 4 {
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p[0] = 1.0; // cyan
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} else {
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p[1] = 1.0; // magenta
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}
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}
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}
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(px, w, h)
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}
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#[test]
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fn traps_the_internal_colour_edge() {
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let (mut px, w, h) = two_blocks();
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let ch = 4;
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trap(&mut px, w, h, ch, 1);
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// At the seam, cyan and magenta now overlap (both inks > 0) in a 1px band on each side.
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let at = |x: usize, y: usize, c: usize| px[(y * w + x) * ch + c];
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assert!(at(3, 0, 1) > 0.5, "magenta spread left into the cyan edge");
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assert!(at(4, 0, 0) > 0.5, "cyan spread right into the magenta edge");
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// Deep inside each block is unchanged (single ink).
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assert_eq!(at(0, 0, 1), 0.0, "far cyan has no magenta");
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assert_eq!(at(7, 0, 0), 0.0, "far magenta has no cyan");
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}
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#[test]
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fn leaves_paper_untouched() {
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let (w, h, ch) = (6usize, 3usize, 4usize);
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let mut px = vec![0.0f32; w * h * ch];
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// One cyan pixel in the middle, rest paper.
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px[(1 * w + 3) * ch] = 1.0;
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let before = px.clone();
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trap(&mut px, w, h, ch, 1);
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// Paper pixels (no ink) stay paper — no ink bleeds into white.
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for i in 0..w * h {
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if before[i * ch] == 0.0 {
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assert_eq!(px[i * ch], 0.0, "paper pixel {i} gained cyan");
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}
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}
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}
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#[test]
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fn width_zero_is_identity() {
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let (mut px, w, h) = two_blocks();
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let orig = px.clone();
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trap(&mut px, w, h, 4, 0);
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assert_eq!(px, orig);
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}
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}
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@ -838,6 +838,7 @@ fn build() -> Vec<CommandSpec> {
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v.extend(crate::pick_cmds::specs());
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v.extend(crate::frame_cmds::specs());
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v.extend(crate::migrate_cmds::specs());
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v.extend(crate::trap_cmds::specs());
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v.extend(crate::variables_cmds::specs());
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v
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}
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@ -57,6 +57,7 @@ pub mod comps_cmds;
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pub mod automate_cmds;
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mod frame_cmds;
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mod migrate_cmds;
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mod trap_cmds;
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mod variables_cmds;
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pub mod pick_cmds;
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pub mod print_cmds;
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@ -0,0 +1,108 @@
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//! Image › Trap. Trapping is a CMYK prepress step (see `photocraft_algo::trap`). Photoshop requires
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//! a flattened CMYK image; we trap the active pixel layer's inks over the canvas. One history step.
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use photocraft_color::ColorMode;
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use photocraft_doc::LayerContent;
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use serde_json::{Value, json};
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use crate::commands::CommandSpec;
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use crate::{EngineError, Result, Session};
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fn enabled(s: &Session) -> std::result::Result<(), String> {
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match s.active() {
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Some(d) if d.doc.mode == ColorMode::Cmyk => Ok(()),
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Some(_) => Err("Trap needs a CMYK document (Image › Mode › CMYK Color)".into()),
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None => Err("no document".into()),
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}
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}
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fn trap(s: &mut Session, p: &Value) -> Result<Value> {
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let cmd = "image.trap";
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let width = p.get("width").and_then(Value::as_f64).unwrap_or(1.0).round().max(0.0) as usize;
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if s.active().ok_or(EngineError::NoDocument)?.doc.mode != ColorMode::Cmyk {
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return Err(EngineError::BadParams { cmd: cmd.into(), msg: "Trap needs a CMYK document".into() });
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}
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s.edit("Trap", |doc, active| {
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let id = active.ok_or(EngineError::NoDocument)?;
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let bounds = doc.bounds();
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let l = doc.layer_mut(id).ok_or(EngineError::NoLayer(id))?;
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let LayerContent::Raster(surf) = &mut l.content else {
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return Err(EngineError::BadParams { cmd: cmd.into(), msg: format!("Trap needs a pixel layer (active layer is a {})", l.content.kind_name()) });
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};
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if bounds.is_empty() {
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return Ok(());
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}
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let ch = surf.channels();
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let (w, h) = (bounds.width() as usize, bounds.height() as usize);
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let mut data = surf.read_region(bounds);
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photocraft_algo::trap::trap(&mut data, w, h, ch, width);
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surf.write_region(bounds, &data);
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Ok(())
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})?;
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Ok(json!({"trapped": true, "width": width}))
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}
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pub fn specs() -> Vec<CommandSpec> {
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vec![CommandSpec {
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id: "image.trap",
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label: "Trap…",
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menu: &["Image"],
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shortcut: None,
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params: r#"{width:px>=1=1} → {trapped,width}: spread inks at colour edges (CMYK only)"#,
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enabled,
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journal: true,
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run: |s, p| trap(s, &p),
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}]
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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use photocraft_geom::Rect;
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#[test]
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fn traps_a_cmyk_document() {
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let mut s = Session::new();
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s.execute("file.new", json!({"width": 8, "height": 4, "mode": "cmyk"})).unwrap();
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// Paint cyan | magenta halves on the Background.
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s.edit("paint", |doc, active| {
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let id = active.unwrap();
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let fmt = doc.pixel_format();
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let l = doc.layer_mut(id).unwrap();
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if let LayerContent::Raster(surf) = &mut l.content {
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let ch = fmt.channels();
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let mut data = vec![0.0f32; 8 * 4 * ch];
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for y in 0..4 {
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for x in 0..8 {
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let px = &mut data[(y * 8 + x) * ch..][..ch];
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if x < 4 { px[0] = 1.0; } else { px[1] = 1.0; }
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if fmt.alpha { px[ch - 1] = 1.0; }
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}
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}
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surf.write_region(Rect::new(0, 0, 8, 4), &data);
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}
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Ok(())
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}).unwrap();
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let r = s.execute("image.trap", json!({"width": 1})).unwrap();
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assert_eq!(r["trapped"], true);
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// The seam now has overlapping inks.
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let st = s.active().unwrap();
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let id = st.active_layer.unwrap();
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if let LayerContent::Raster(surf) = &st.doc.layer(id).unwrap().content {
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let ch = surf.channels();
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let d = surf.read_region(Rect::new(0, 0, 8, 4));
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assert!(d[(3) * ch + 1] > 0.5, "magenta trapped into the cyan edge");
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assert!(d[(4) * ch + 0] > 0.5, "cyan trapped into the magenta edge");
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}
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// One history step.
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assert_eq!(st.history.entries().last().map(|e| e.as_str()), Some("Trap"));
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}
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#[test]
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fn rejects_non_cmyk() {
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let mut s = Session::new();
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s.execute("file.new", json!({"width": 8, "height": 4, "mode": "rgb"})).unwrap();
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assert!(s.execute("image.trap", json!({"width": 1})).is_err());
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}
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}
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@ -7,7 +7,7 @@ use crate::menu_catalog::CATALOG;
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use crate::menus::is_live;
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/// Minimum number of live catalog items. Raise it when parity grows; never lower it.
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pub const FLOOR: usize = 602;
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pub const FLOOR: usize = 603;
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/// One top-level menu's coverage.
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#[derive(Clone, Debug, serde::Serialize)]
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@ -2,13 +2,13 @@
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Generated by `cargo xtask parity` from `crates/ui-egui/src/menu_catalog.rs` (Photoshop's menu tree) and the live command registry. Do not edit by hand.
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**607 of 625 menu items live (97.1%).**
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**608 of 625 menu items live (97.3%).**
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| Menu | Live | Total | % |
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|---|---:|---:|---:|
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| File | 47 | 50 | 94% |
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| Edit | 75 | 75 | 100% |
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| Image | 60 | 61 | 98% |
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| Image | 61 | 61 | 100% |
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| Layer | 147 | 160 | 92% |
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| Type | 44 | 44 | 100% |
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| Select | 25 | 25 | 100% |
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@ -24,10 +24,6 @@ Generated by `cargo xtask parity` from `crates/ui-egui/src/menu_catalog.rs` (Pho
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- Import › Video Frames to Layers… (`file.import.videoFramesToLayers`)
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- Import › WIA Support… (`file.import.wiaSupport`)
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### Image (1)
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- Trap… (`image.trap`)
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### Layer (13)
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- Video Layers › New Blank Video Layer (`layer.videoLayers.newBlankVideoLayer`)
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