Edit Colors: convert embedded images to indexed color

Edit > Edit Colors > Convert to Indexed Color... (edit.colors.toIndexed) stores the embedded images in the selection as indexed-color PNGs: a palette of at most 256 RGB colors, each pixel the index of one. The dialog previews live and OK is one undo step. - The palette is chosen as for a PNG-8 export (selective, perceptual, adaptive, web, gray, black and white), as evenly spaced levels of red, green and blue (uniform), or from the document's swatches. Dithering is diffusion, pattern, noise or none, with an amount. - Pixels under half opacity become one transparent entry; the others become opaque in their own color. Linked images, colorized images and color glyph images keep their pixels. - An image that is already an indexed PNG and would show the same pixels is left as it is, and no undo step is recorded when no image changes. - An image of more than 134,217,728 pixels (33,554,432 in the web app) is refused, read from its header before decoding. - With Select All, locked and hidden objects that hold an image that is not an indexed PNG yet are counted in notChanged, without converting them. - The quantizer gains quantize_to, which maps pixels to a given palette. Docs: docs/mcp.md, docs/target-app-parity.md.
2026-11-15 13:36:53 +00:00 · 2026-11-13 09:49:00 -08:00
parent f520e6f8c5
commit 81d19f1718
44 changed files with 770 additions and 23 deletions
@@ -484,6 +484,250 @@ fn adjust_colors_converting_to_gray_stores_an_image_as_grayscale() {
    assert!(source(false).is_none(), "the colors keep their model");
 }

+/// Convert to Indexed Color stores an image as a palette PNG in one undo step; an image with few
+/// enough colors keeps them, and converting it again changes nothing and adds no undo step.
+#[test]
+fn convert_to_indexed_stores_an_image_as_a_palette_png() {
+    let mut s = session();
+    let id = image_node(&mut s);
+    let undo = s.doc().unwrap().history.undo.len();
+    let r = s.execute("edit.colors.toIndexed", &json!({})).unwrap();
+    assert_eq!(r["changed"], 1, "{r}");
+    let key = image_key(&s, id);
+    assert!(s.doc().unwrap().doc.images[&key].indexed_png(), "an indexed PNG");
+    assert_eq!(pixels(&s, id), [[255, 0, 0, 255], [0, 255, 0, 255], [0, 0, 255, 255], [255, 255, 255, 255]], "half opaque becomes opaque");
+    assert_eq!(s.doc().unwrap().history.undo.len(), undo + 1);
+    let again = s.execute("edit.colors.toIndexed", &json!({})).unwrap();
+    assert_eq!(again["changed"], 0, "{again}");
+    assert_eq!(image_key(&s, id), key);
+    assert_eq!(s.doc().unwrap().history.undo.len(), undo + 1, "no undo step when nothing changes");
+    s.execute("edit.undo", &json!({})).unwrap();
+    assert_eq!(pixels(&s, id)[3], [255, 255, 255, 128], "one undo step restores the image");
+}
+
+/// Pixels under half opacity become transparent; an indexed image converted to a palette it
+/// already shows is left as it is, and one converted to a smaller palette changes.
+#[test]
+fn convert_to_indexed_keeps_transparency_and_reduces_an_indexed_image() {
+    let mut s = session();
+    let id = image_of(&mut s, [[200, 30, 90, 255], [20, 40, 220, 255], [0, 0, 0, 100], [250, 250, 250, 255]]);
+    s.execute("edit.colors.toIndexed", &json!({"dither": "none"})).unwrap();
+    assert_eq!(pixels(&s, id)[2][3], 0, "under half opacity: transparent");
+    let r = s.execute("edit.colors.toIndexed", &json!({"reduction": "blackWhite", "dither": "none"})).unwrap();
+    assert_eq!(r["changed"], 1, "{r}");
+    let px = pixels(&s, id);
+    assert_eq!([px[0], px[1], px[3]], [[0, 0, 0, 255], [0, 0, 0, 255], [255, 255, 255, 255]]);
+    assert_eq!(px[2][3], 0);
+}
+
+/// The uniform reduction takes evenly spaced levels of each channel, and the document reduction
+/// the colors of the document's swatches.
+#[test]
+fn convert_to_indexed_uses_a_uniform_or_the_document_palette() {
+    let mut s = session();
+    let id = image_of(&mut s, [[200, 30, 90, 255], [20, 40, 220, 255], [120, 130, 140, 255], [250, 250, 250, 255]]);
+    s.execute("edit.colors.toIndexed", &json!({"reduction": "uniform", "colors": 9, "dither": "none"})).unwrap();
+    assert_eq!(pixels(&s, id), [[255, 0, 0, 255], [0, 0, 255, 255], [0, 255, 255, 255], [255, 255, 255, 255]]);
+    s.execute("edit.undo", &json!({})).unwrap();
+    s.execute("edit.colors.toIndexed", &json!({"reduction": "document"})).unwrap();
+    let swatches: Vec<[u8; 3]> = crate::cmd::swatchlib::library_colors(&s, "document")
+        .unwrap()
+        .iter()
+        .map(|c| {
+            let [r, g, b, _] = c.to_rgba8(1.0);
+            [r, g, b]
+        })
+        .collect();
+    for p in pixels(&s, id) {
+        assert!(swatches.contains(&[p[0], p[1], p[2]]), "{p:?} is a swatch color");
+    }
+}
+
+/// The start of a PNG of `w` × `h` RGBA pixels: its header and a first image data chunk, without
+/// the rest of the pixels.
+fn png_header(w: u32, h: u32) -> Vec<u8> {
+    let crc = |data: &[u8]| {
+        let mut c = !0u32;
+        for &b in data {
+            c ^= u32::from(b);
+            for _ in 0..8 {
+                c = if c & 1 == 1 { 0xEDB8_8320 ^ (c >> 1) } else { c >> 1 };
+            }
+        }
+        !c
+    };
+    let chunk = |ty: &[u8; 4], data: &[u8]| {
+        let body = [ty.as_slice(), data].concat();
+        [(data.len() as u32).to_be_bytes().as_slice(), &body, &crc(&body).to_be_bytes()].concat()
+    };
+    let ihdr = [w.to_be_bytes().as_slice(), &h.to_be_bytes(), &[8, 6, 0, 0, 0]].concat();
+    [b"\x89PNG\r\n\x1a\n".as_slice(), &chunk(b"IHDR", &ihdr), &chunk(b"IDAT", &[0x78, 0x9c, 0x03, 0x00])].concat()
+}
+
+/// An image larger than Convert to Indexed Color converts is refused by its size, read from the
+/// file's header, before any pixel is decoded; nothing changes.
+#[test]
+fn convert_to_indexed_refuses_an_image_too_large_to_convert() {
+    let mut s = session();
+    let id = image_node(&mut s);
+    assert_eq!(vectorcraft_doc::ImageBlob::png(png_header(30_000, 30_000)).pixel_size(), Some((30_000, 30_000)));
+    s.edit("Swap", |d, _| {
+        d.images.insert("pic".into(), vectorcraft_doc::ImageBlob::png(png_header(30_000, 30_000)));
+        Ok(())
+    })
+    .unwrap();
+    let undo = s.doc().unwrap().history.undo.len();
+    let e = s.execute("edit.colors.toIndexed", &json!({})).unwrap_err().to_string();
+    assert!(e.contains("an image of 30000 × 30000 pixels is too large to convert"), "{e}");
+    assert_eq!(image_key(&s, id), "pic");
+    assert_eq!(s.doc().unwrap().history.undo.len(), undo);
+}
+
+/// Convert to Indexed Color refuses parameters it can't use, and leaves the image as it is.
+#[test]
+fn convert_to_indexed_refuses_bad_params() {
+    let mut s = session();
+    let id = image_node(&mut s);
+    for (p, msg) in [
+        (json!({"colors": 1}), "`colors` must be a whole number from 2 to 256"),
+        (json!({"colors": 257}), "`colors` must be a whole number from 2 to 256"),
+        (json!({"colors": "8"}), "`colors` must be a whole number from 2 to 256"),
+        (json!({"colors": 16.5}), "`colors` must be a whole number from 2 to 256"),
+        (json!({"reduction": "uniform", "colors": 8}), "`colors` must be at least 9 for the uniform reduction"),
+        (json!({"reduction": "document", "colors": 16}), "`colors` does not apply to the document reduction"),
+        (json!({"reduction": "blackWhite", "colors": 2}), "`colors` does not apply to the blackWhite reduction"),
+        (json!({"reduction": "posterize"}), "unknown reduction `posterize`"),
+        (json!({"dither": "random"}), "unknown dither `random`"),
+        (json!({"ditherAmount": 101}), "`ditherAmount` must be a number from 0 to 100"),
+        (json!({"ditherAmount": "50"}), "`ditherAmount` must be a number from 0 to 100"),
+    ] {
+        let e = s.execute("edit.colors.toIndexed", &p).unwrap_err().to_string();
+        assert!(e.contains(msg), "{p}: {e}");
+    }
+    assert_eq!(image_key(&s, id), "pic");
+}
+
+/// An embedded `w` × `h` image of the pixels `f(x, y)`, placed and selected.
+fn placed(s: &mut Session, w: u32, h: u32, f: impl Fn(u32, u32) -> [u8; 4]) -> NodeId {
+    let mut png = Vec::new();
+    image::RgbaImage::from_fn(w, h, |x, y| image::Rgba(f(x, y))).write_to(&mut std::io::Cursor::new(&mut png), image::ImageFormat::Png).unwrap();
+    let r = s.execute("file.place", &json!({"name": "art.png", "dataBase64": vectorcraft_format::base64_encode(&png)})).unwrap();
+    NodeId(r["ids"][0].as_u64().unwrap())
+}
+
+/// `ids` picks the images to convert; a linked image and a colorized image keep their pixels.
+#[test]
+fn convert_to_indexed_takes_ids_and_leaves_linked_and_colorized_images() {
+    let mut s = session();
+    let a = placed(&mut s, 2, 1, |x, _| [200, 30 + x as u8, 90, 255]);
+    let b = placed(&mut s, 2, 1, |x, _| [20, 40, 200 + x as u8, 255]);
+    let (ka, kb) = (image_key(&s, a), image_key(&s, b));
+    s.execute("select.set", &json!({"ids": [a.0]})).unwrap();
+    let r = s.execute("edit.colors.toIndexed", &json!({"ids": [b.0]})).unwrap();
+    assert_eq!(r["changed"], 1, "{r}");
+    assert_eq!(image_key(&s, a), ka, "not in `ids`");
+    assert_ne!(image_key(&s, b), kb);
+    s.edit("Link", |d, _| {
+        let NodeKind::Image(im) = &mut d.node_mut(a).unwrap().kind else { panic!("not an image") };
+        im.link = Some(vectorcraft_doc::LinkInfo::new("art.png"));
+        Ok(())
+    })
+    .unwrap();
+    let undo = s.doc().unwrap().history.undo.len();
+    let r = s.execute("edit.colors.toIndexed", &json!({"ids": [a.0]})).unwrap();
+    assert_eq!(r["changed"], 0, "a linked image: {r}");
+    assert_eq!(image_key(&s, a), ka);
+    assert_eq!(s.doc().unwrap().history.undo.len(), undo, "no undo step");
+    let mut png = Vec::new();
+    image::GrayImage::from_pixel(4, 4, image::Luma([90])).write_to(&mut std::io::Cursor::new(&mut png), image::ImageFormat::Png).unwrap();
+    let r = s.execute("file.place", &json!({"name": "gray.png", "dataBase64": vectorcraft_format::base64_encode(&png)})).unwrap();
+    let gray = NodeId(r["ids"][0].as_u64().unwrap());
+    s.execute("paint.setFill", &json!({"ids": [gray.0], "color": "#ff0000"})).unwrap();
+    assert!(s.doc().unwrap().doc.node(gray).unwrap().extras().colorize.is_some(), "the fill colorizes the image");
+    let kg = image_key(&s, gray);
+    let r = s.execute("edit.colors.toIndexed", &json!({"ids": [gray.0]})).unwrap();
+    assert_eq!(r["changed"], 0, "a colorized image: {r}");
+    assert_eq!(image_key(&s, gray), kg);
+}
+
+/// With the selection Select All makes, locked and hidden images are left out and counted in
+/// `notChanged`; a left-out image too large to convert is counted without an error.
+#[test]
+fn convert_to_indexed_counts_left_out_images() {
+    let mut s = session();
+    let a = placed(&mut s, 2, 1, |x, _| [200, 30 + x as u8, 90, 255]);
+    let locked = placed(&mut s, 2, 1, |x, _| [20, 40, 200 + x as u8, 255]);
+    let hidden = placed(&mut s, 2, 1, |x, _| [120, 140 + x as u8, 20, 255]);
+    s.edit("Huge", |d, _| {
+        let NodeKind::Image(im) = &mut d.node_mut(locked).unwrap().kind else { panic!("not an image") };
+        im.key = "huge".into();
+        d.images.insert("huge".into(), vectorcraft_doc::ImageBlob::png(png_header(30_000, 30_000)));
+        Ok(())
+    })
+    .unwrap();
+    s.execute("object.lock", &json!({"ids": [locked.0]})).unwrap();
+    s.execute("object.hide", &json!({"ids": [hidden.0]})).unwrap();
+    s.execute("select.all", &json!({})).unwrap();
+    let kh = image_key(&s, hidden);
+    let r = s.execute("edit.colors.toIndexed", &json!({})).unwrap();
+    assert_eq!(r["changed"], 1, "{r}");
+    assert_eq!(r["notChanged"], json!({"locked": 1, "hidden": 1}), "{r}");
+    assert!(r["warning"].is_string(), "{r}");
+    assert!(s.doc().unwrap().doc.images[&image_key(&s, a)].indexed_png());
+    assert_eq!((image_key(&s, locked), image_key(&s, hidden)), ("huge".to_string(), kh));
+}
+
+/// The uniform reduction takes the most levels a channel whose cube leaves one entry for
+/// transparency (3 for 64 colors, 6 for 256), and the document reduction takes 1 to 255 swatch
+/// colors.
+#[test]
+fn convert_to_indexed_sizes_the_uniform_and_document_palettes() {
+    let mut s = session();
+    let id = image_of(&mut s, [[200, 30, 90, 255], [20, 40, 220, 255], [120, 130, 140, 255], [250, 250, 250, 255]]);
+    s.execute("edit.colors.toIndexed", &json!({"reduction": "uniform", "colors": 64, "dither": "none"})).unwrap();
+    assert_eq!(pixels(&s, id), [[255, 0, 127, 255], [0, 0, 255, 255], [127, 127, 127, 255], [255, 255, 255, 255]]);
+    s.execute("edit.undo", &json!({})).unwrap();
+    s.execute("edit.colors.toIndexed", &json!({"reduction": "uniform", "dither": "none"})).unwrap();
+    assert_eq!(pixels(&s, id), [[204, 51, 102, 255], [0, 51, 204, 255], [102, 153, 153, 255], [255, 255, 255, 255]]);
+    s.execute("edit.undo", &json!({})).unwrap();
+    s.edit("No swatches", |d, _| {
+        d.swatches.clear();
+        d.swatch_groups.clear();
+        Ok(())
+    })
+    .unwrap();
+    let e = s.execute("edit.colors.toIndexed", &json!({"reduction": "document"})).unwrap_err().to_string();
+    assert!(e.contains("the document has no color swatches"), "{e}");
+    s.edit("Many swatches", |d, _| {
+        for i in 0..256u32 {
+            let paint = Paint::solid(Color::rgb8(i as u8, 7, 9));
+            d.swatches.push(vectorcraft_color::swatch::Swatch { name: format!("c{i}"), paint, global: false, spot: false });
+        }
+        Ok(())
+    })
+    .unwrap();
+    let e = s.execute("edit.colors.toIndexed", &json!({"reduction": "document"})).unwrap_err().to_string();
+    assert!(e.contains("the document's swatches hold 256 colors; the document reduction takes at most 255"), "{e}");
+    assert_eq!(image_key(&s, id), "pic");
+}
+
+/// `dither` and `ditherAmount` reach the quantizer: a gray ramp reduced to black and white is
+/// dithered by each method, and at an amount of 0 it comes out as with no dither.
+#[test]
+fn convert_to_indexed_dithers_by_the_amount_given() {
+    let ramp = |p: Value| {
+        let mut s = session();
+        let id = placed(&mut s, 16, 4, |x, _| [(x * 17) as u8, (x * 17) as u8, (x * 17) as u8, 255]);
+        s.execute("edit.colors.toIndexed", &p).unwrap();
+        pixels(&s, id)
+    };
+    let none = ramp(json!({"reduction": "blackWhite", "dither": "none"}));
+    for d in ["diffusion", "pattern", "noise"] {
+        assert_eq!(ramp(json!({"reduction": "blackWhite", "dither": d, "ditherAmount": 0})), none, "{d} at 0");
+        assert_ne!(ramp(json!({"reduction": "blackWhite", "dither": d})), none, "{d} at 100");
+    }
+}
+
 /// A PDF of a CMYK document writes an image Convert to Grayscale made with one channel (#5632).
 #[test]
 fn a_converted_image_is_written_to_pdf_as_gray_in_a_cmyk_document() {
@@ -368,6 +368,7 @@ fn ids_cases(d: u64) -> Vec<(&'static str, &'static str, serde_json::Value, Unse
        ("edit.colors.invert", "ids", json!({}), Selected),
        ("edit.colors.toCMYK", "ids", json!({}), Selected),
        ("edit.colors.toGrayscale", "ids", json!({}), Selected),
+        ("edit.colors.toIndexed", "ids", json!({}), Selected),
        ("edit.colors.toRGB", "ids", json!({}), Selected),
        ("edit.colors.saturate", "ids", json!({"intensity": 50}), Selected),
        ("edit.colors.adjustBalance", "ids", json!({"r": 20}), Selected),