A JPEG rounds each 8 x 8 block's tone on its own, which leaves a small
step at every block edge. Where a dark ground changes slowly, those steps
decided which of two palette colors a whole block got, and the trace
followed the block edges as a staircase.
The new deblock pass finds the block grid in the image: the mean step
between neighboring opaque pixels must peak at the same one of eight
positions at both block edges of a 16 px span, across and down. Cropped
JPEGs and JPEGs saved in another format are found the same way; pictures
of flat 8 x 8 cells are not. At each block edge, a stretch of eight lines
whose step is under the limit and whose pixels hold no edge has the step
spread over the eight pixels around the edge, as the deblocking filters
of ITU-T H.263 Annex J and MPEG-4 Part 2 Annex F.3.1 do. Larger steps are
kept. The limit, the edge guard and how much of each line's own step is
smoothed depend on the mode: Black and White smooths only the smallest
steps, and traces of more than 16 colors move every line of a stretch
by the same amount. The pass runs before the photo pre-filter and works
in strips of rows, so only its output is as large as the image.
The Limited palette's median cut ranks cuts by pixel-weighted gain. A
large near-black ground with faint noise therefore took two colors less
than 0.02 apart in Oklab, and the trace drew blotches of one over the
other.
With 9 to 16 colors, a cut whose two sides both have a dark gray mean
(Oklab lightness under 0.30, chroma under 0.03) and lie less than 0.03
apart now has its gain scaled by (distance / 0.03)^2 while the cut is
chosen. The ground keeps one color, and the color it would have taken
goes to another cut. Document Library without swatches follows Limited.
Other color counts, Full Tone and Automatic choose the same cuts as
before.
The runs of transparent and left-out pixels that the first round checks
holes against were kept in a list for each row. A tall, narrow image paid
a list header for every row: 1.1 MB for a 3 x 20,000 pixel image with
two runs. The runs are now one list over the whole image, so they take
at most four bytes a pixel, as the half-gigabyte bound counts them.
The overlapping test now traces the same image eight times with several
levels found at a time and compares each result with the one traced a
level at a time. The doc comment of the stacked rounds says that the
components kept for the second pass take up to 256 MiB outside the half
gigabyte that sets how many levels are traced at once.
An Overlapping layer covers the colors above it within its area, so an
area of another color that a shape enclosed was a hole in that shape
and in the shape of every layer around it, and its outline was fitted
once for each of them. In a code-drawn test, a white disc in a black
ring that four grays touch had six copies of its outline.
With Fills and without Create Strokes, each shape is now filled whole,
by a fill rule of VectorCraft's own. The area inside a filled hole is
traced on its own and drawn after the shapes around it, so its outline
is fitted once. An area of one color is drawn from the hole's outline.
A shape keeps a hole where the area holds a transparent pixel or a
color that Ignore Color or Keep Colors leaves out, and a hole smaller
than Noise is filled with the shape's color as before. Nested areas are
traced within a work budget of VectorCraft's own: four times the
image's pixels (counted as at least 65,536) times its colors, each area
costing its box times its colors. An area that costs more than what is
left keeps its holes and is not charged. Create Strokes and outlines
without Fills are unchanged.
Shapes have holes only in those cases, there are more paths, and the
stacking order changes. Expand by Color starts another group of a color
where an area is drawn above the shape around it. The trace's progress
counts finer steps across the rounds of enclosed areas, not one step
per color layer.
A layer's components without its own color are now left out after its
mask is traced, instead of in a labeling pass before it. Every route
finds its components through the same function.
A blend pixel took a side of its edge only when the picture's own colors
on both sides lay within 2 px of it. With a limited palette, an edge
blurred over more than about 4 px kept the middle of its ramp in the
palette's in-between tones, which traced as rings of thin paths around
the edge.
With a Limited palette of at most 16 colors (3 Colors, 6 Colors,
16 Colors) and in Grayscale with at most 16 grays (Shades of Gray),
settled_wide looks for the own colors within 8 px, pairs the 8 of them
nearest to the pixel's color, and moves the pixel to the nearer side of
the best pair when that pair explains it twice as well as its own color,
or when it lies between the two and off the line between them by less
than 0.15 of their distance apart. These values are VectorCraft's own.
Of two pairs that explain it equally well it takes the closer one. A
pixel keeps its color when an own pixel of that color lies within 4 px
or when its color is one of the pair. Grayscale compares lightness. The
colors within reach are kept as bitsets for a strip of 7 columns at a
time.
High Fidelity Photo, Low Fidelity Photo, Black and White and the other
palettes keep the 2 px rule unchanged.
On the quality harness, blurred and scanned flat art with 6 and
16 Colors goes from 6 to 9 paths to 3, and from 0.23 to 0.26 px off to
0.07 to 0.11. Askew shapes take up to 11 px more area in colors the art
does not have, thin lines with 16 Colors lose more (largest distance
23.5 to 45.3 px), and Shades of Gray traces thin lines in 7.3 paths
where it took 5.3.
Noisy images settle more of their pixels: the dense grouping test
traces 150 x 150 noise instead of 120 x 120 to keep more than its 500
paths.
Covers the limited-palette part of #1911 (leogrox).
Docs: docs/target-app-parity.md, docs/image-trace-quality.md.
Stroke is the widest feature that can be stroked, and it was applied to
each connected shape as a whole: a thick body with thin arms stayed one
filled area. Now a shape wider than Stroke somewhere keeps as its area
every disc wider than Stroke that fits in it, and each piece outside
those discs that reaches out of them at least one and a half times its
own width (and 3 px) is traced as a stroked center line. A line's end at
the area goes to the cut, so the line's cap closes the join. Corners and
edge slivers stay in the area, and a piece that cannot be traced stays
in it too. Shapes no wider than Stroke trace as before.
Each line keeps one width; without Fills, the area is still a 1 px
outline.
Docs: docs/target-app-parity.md.
Color and Grayscale traces smoothed a gray photo before choosing its
colors, but a tinted photo with the same tones skipped smoothing: the
0.065 error rule applied only to pictures whose channels stay within 8
levels of each other. A picture whose opaque pixels lie, 19 in 20, within
6 levels of one tone curve now takes the same rule. The curve runs
through the median color of each 8-level stretch along the colors' main
direction, and a pixel on it must also lie within 6 levels of the plane
the colors spread along most, so art in several unrelated colors is not
counted. The sixteen-versus-eight exception still keeps clean flat art
on the flat-art route.
In a gradient or a shaded area the palette colors on either side of a band
border differ by more than the image changes across it, so pixel noise
decided where the border ran, and it was smoothed over 0.5 px like a real
edge: borders wobbled, kept stair steps and took many anchors.
Each crack between two colors now records how much of the step between
them the image makes next to it and a few pixels further out, how much the
image changes there along the line between the two colors and in any
direction, and how much it changes within each side (RGB distances, 0 to
255 a channel). A piece of outline is the contour of a smooth area when its
cracks show less than half of the step; either more of it further out, a
change along the line under 12, or no opaque pixels further out; some change
within the sides, at least 1/32 of the change along the line; and a whole change
under twice the change along the line, or under 24. Such a piece is
smoothed over 4 px (a closed one over at most an eighth of its smaller
width or height), keeps no corners, is fitted to at least 0.5 px and is
checked against its smoothed points. The values are the same from either
side of the crack.
Grayscale reads each pixel as its gray, for this rule and for every edge's
sub-pixel shift, which compared the pixels' colors with gray palette
entries.
Color traces of clean flat-color art and Black and White traces are
unchanged. Specks rise by up to 0.8 per image on gradient and photo
inputs, and Auto Color with Shapes leaves a 0.3 px gap there.
Docs: docs/target-app-parity.md, docs/image-trace-quality.md.
The continuous-tone test asked whether 8 colors leave more than a tenth
of the error of one color. A gray picture's tones lie along one line,
where 8 colors come nearer to them, so some gray photos scored 0.078 to
0.093 and were traced as flat art, without the smoothing color photos
get. Their noise then mixed neighboring tones (a 16 Colors trace could
keep 10 or 12 colors) and stepped the edges.
A picture with at least 95% of its opaque pixels within 8 levels across
their channels now also counts as continuous tone when 8 colors leave
more than 0.065 of the error of one color, unless 16 colors leave at
most a fifth of the error of 8. These are VectorCraft's own values. The
exception keeps gray flat art of up to 16 clean levels on its old
route. Pictures with more than 5% of their opaque pixels outside that
8-level range are unchanged.
Anti-aliased or noisy gray flat art can now take the smoothed route as
well. Very noisy gray scans of flat art get fewer specks and staircase
edges; some gray illustrations and sketches get more anchors and
staircase edges at 16 Colors and High Fidelity Photo. Some 16 Colors
and High Fidelity Photo palettes of gray photos grow toward the
requested count, with more anchors and regions, and some 6 Colors
traces get more staircase edges.
The fitter accepted a piece at depth 14, or with fewer than six points,
whatever its error, so a traced outline could stay farther than the
tolerance from its points. Synthetic 2 px block noise at Paths 100 and
Corners 0 kept a piece 2.7 px off at a tolerance of 0.1.
Such a piece is now accepted only when each point is within the tolerance
of the curve. Otherwise a short run is cut at its worst point, down to
two points, and a run at the depth limit is cut in the middle, which keeps
the recursion shallow. Every other piece is unchanged. Noisy art can get
more anchors.
a_traced_pixel_that_straightens_to_no_area_... now traces at Paths 80. At
Paths 90 that pixel's no-area result came from pieces over the tolerance.
Tracing a photo or a large image ran inside imageTrace.make on the UI
thread, so the window froze for as long as the trace took, with nothing
to say it was working.
A trace the user asks for (Object > Image Trace > Make and Make and
Expand, the task bar's Image Trace, the Image Trace panel's Trace and
presets) now runs on a thread of its own, as heavy plug-in filters do.
The status bar says so, and after 0.4 s a progress window shows how
many of the image's colors are traced, with Cancel and Continue in
Background (imageTrace.cancelRuns, imageTrace.hideRuns).
The result goes back to the command it was prepared for
(cmd::TraceRun, Traced::hand_in), which takes it only for the same
object, image and settings, so the edit is one undo step as before. A
newer trace of the same object replaces one still running, and a trace
whose image or settings changed meanwhile changes nothing. The control
channel, MCP, scripts and the web trace at once, as before.
The tracer reports its stages and color layers to a callback and stops
when it says so (trace_watched).
The loop that keeps rare colors stopped at the first color past the
budget of six, so a cut-edge blend listed after it was not recorded as
tracing as its rare color, even when that rare color was kept, and its
pixels went to the nearest color instead. The loop now goes on past the
budget and only stops keeping new rare colors. It moves into
`kept_rare`, which a new test calls with seven rare colors and a blend
of the first.
The test of an outline over a cut edge in the color of other art also
checks that the dark paths reach the top and the bottom of the disc,
which no bar comes near: before, the bars alone met its checks.
The test of a color whose every path straightens to no area traced a
pale blue row with a library of a light color, black and [40, 120, 240].
With Document Library weighing hue and chroma three times as much as
lightness, the row takes the light color instead of that blue, so the
test no longer traced any blue. The library blue is now [60, 130, 235],
which the row still maps to; the assertions are unchanged.
With the Document Library palette, each pixel took the library color
nearest in plain Oklab distance. A 50% gray lies nearer in that distance
to a saturated blue of the same lightness than to black or a light
cream, and a muted brown is also nearer to the blue than to either. With
a black, cream and blue library, both traced as the blue.
This changes how Document Library matches pixels: each pixel now takes
the library color nearest with differences in hue and chroma (Oklab a
and b) counted three times as much as lightness. The same measure picks
which library colors are used. Neutral and muted tones take a neutral
library color, and the other palettes are unchanged.
With Method Overlapping, each color layer covered every pixel of the colors
above it in the stack. A small dot or square on a background was then traced
once in its own color and again, at the same bounds, in every color between
the background and it, and with Shapes on each copy became its own live shape.
Those layers also ended on edges they never touched and showed through the
anti-aliased rim there.
Each layer now leaves out every 4-connected part of its stacked area that holds
no pixel of its own color. This changes the result of many Overlapping traces,
the photo presets included: fewer paths (High Fidelity Photo 121 to 69.6 on its
own quality inputs, Low Fidelity Photo 37.1 to 26.1) and no rim, around a
shape, of a color that sits apart from it. One existing test that counted the
extra copies now expects one layer per area, and another that compared layer
pixel counts now checks that the bottom layer covers the whole image.
Since main leaves a color with no paths out of the trace's palette, an
empty palette no longer shows that Ignore Color left out every color
keepColors matches. The trace result now says so in keep_ignored, and
the warning reads it, so a matched color that produces no paths is
reported as such with Ignore White on.
A filled path that straightens to no area is left out of the trace
(#3949). When that removed every path of a color, the color stayed in
the trace's palette, so the Image Trace panel's Colors count and the
`colors` that `imageTrace.make` returns included it. The palette now
lists only the colors that have a path.
A pixel on the edge of a cut-out image with an alpha of 128 or more was
traced with its own color. When that color was a darkened edge tone, it
took whichever palette color lay nearest, and the edge traced as 1 px
slivers of a color that appears nowhere near it.
In Color and Grayscale, a pixel with an alpha of 128 to 254 next to a
pixel under half opaque now takes a color of the fully opaque pixels
within two pixels of it when its own color is that color or a darker
shade of it, counting only pixels it reaches without crossing a
transparent gap; of several such colors, it takes the one the most of
those pixels have. It keeps its own color when one of those pixels has
it, or when its color is not a shade of any of theirs, so a thin
semi-transparent outline of another color stays as it is. Ties go to the color nearest its own, by its gray
in Grayscale. Opaque images trace as before.
Fitting straightens the pieces of an outline that lie close to a line, and
Snap Curves To Lines straightens more of them. The outline of a single
pixel, or of a region one pixel thick along an edge such as an opaque row
of a mid tone under a light shape, can then have all its pieces on one
line. The trace held a selectable path with no area, for example a path
140 x 0 px with Snap Curves To Lines.
In a Color, Grayscale or Black and White trace with Fills, a fitted
outline or hole whose area is below 1e-6 px^2 is now left out. A path
with no area paints nothing, so the traced result paints the same pixels
as before. Without Fills, the 1 px stroke that outlines each area draws
such a loop, so it is kept. A single closed loop keeps its area as
before.
Image Trace had no way to trace some of an image's colors and leave the
rest out. Ignore Color drops one color, so tracing only the line work of
a multi-color image took a full trace and then deleting the other
colors' paths by hand.
With "keepColors": ["#rrggbb", ...] in the params of imageTrace.make and
imageTrace.makeAndExpand, only the palette colors within about 30 levels
of a listed color are traced, the distance Ignore Color matches by. With
Method Abutting, the kept colors' paths are the same as in a trace of
every color. With Method Overlapping, a kept color's paths do not reach
under the colors left out, as with Ignore Color. An empty list traces
every color, and a value that is not a six-digit hex color is refused.
Flat Logo mode does not use the list.
The reply's warnings name each listed color that matches none of the
colors the trace found, and say when nothing was traced; the status bar
shows the first. The warnings are translated in every complete catalog.
The params help of imageTrace.make lists keepColors and the new
warnings, and the help of imageTrace.makeAndExpand lists the warnings
it returns.
The Automatic palette counts flat art's colours by area (a colour needs
about 1% of the picture, 0.5% at Colors 100) and fits that count with
median cut and area-weighted k-means. A stem, a highlight, or a near
white beside a pale background (within 24 levels, so in one box) was
averaged into a large neighbour; mixed-colour merging and Noise could
then remove what was left.
On the flat route only, after the count is fitted, rare_colours finds
the colours too rare or too close for it and keeps those that are
distinct (at least 2.5 in Oklab x 100 from every palette colour and from
the main colour each stands for), flat (mostly one histogram bin) and
drawn (a 4-connected region of their own unblended pixels of at least 8
pixels, or three of at least 4); a colour lying between two others, as
anti-aliasing mixes them, must also have an inside. At most six, largest
region first. They stay fixed while the other colours are refitted
around them; merge_mixed leaves them alone; denoise_keeping keeps their
regions of 4 pixels or more whatever Noise is (smaller specks still go).
Full Tone, Limited and Automatic's continuous-tone route are unchanged,
and denoise without kept labels is as before.
Methods cited in the code: median cut (Heckbert 1982), k-means (Lloyd
1982), Oklab (Ottosson 2020), salient-colour preservation (Fukuda et al.
2019, doi:10.1117/12.2521607). The rule and its numbers are VectorCraft's
own; Adobe does not document how its palettes are chosen.
Tests (code-drawn): a rare stem or patch over 2-8 flat colours, hard
and anti-aliased at 1x and 2x; near-white highlights on #FFF4E0 kept and
still paths at Noise 16; a 3 px #909090 stem on #808080; scattered
single pixels of the same areas add no colour; denoise_keeping at Noise
0-32.
Measured on 66 synthetic flat logos (22 designs x hard 1x, anti-aliased
1x and 2x; local inputs): every key colour and no spurious one in 66
(was 39); missing key colours 0 (was 43), spurious 0 (was 2), merged
pairs 0 (was 46); rendered dE00 0.348 -> 0.138. Four public-domain scan
crops take the continuous-tone route and are unchanged.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018tBcdwNhptqtmX32JCGFzB
Raster::new checked its RGBA length with assert_eq!, so bytes of the
wrong length (from a file, a plug-in or a control message) would abort
instead of reporting an error. It now returns Result<Raster, TraceError>
and gives TraceError::Decode naming the byte count and the size (the
existing variant, whose text is already translated, instead of a new
message every language would need). The size product is checked for
overflow.
Raster::pixel indexed the bytes directly; it now gives transparent
black outside the raster, or past the end of a raster whose public
fields were set to a size its bytes don't have (which mosaic reads).
The public signature changes: every caller in the workspace was a test
(trace unit tests, Flat Logo tests and the quality harness), updated to
unwrap. No shipped code built a Raster with new; decode, decode_to_fit
and from_fn always make the right length, and trace_within already
refuses a raster whose fields disagree.
Test (code-drawn): a_raster_of_the_wrong_length_is_an_error_not_a_crash
(short, long, empty, zero-width and overflowing sizes; pixel, trace and
mosaic on a raster whose fields disagree).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018tBcdwNhptqtmX32JCGFzB
A small closed loop whose fit collapsed to a single cubic (fit_closed),
or a piece returning to its own junction with fewer than two fitted
cubics (fit_piece), kept every positioned point as a straight segment.
A looser Paths collapses more loops, so it could give more segments
than a tighter one.
Such a loop now tries the fewest segments that still hold it, each only
if the result keeps an area (more than 0.25 px^2) and stays within
1.5 * max(tolerance, 0.5 px) of the points both ways: the fit at up to
three somewhat tighter tolerances (what a slightly higher Paths gives);
for a closed loop then two cubics split at its start and its farthest
point, then the outline simplified at the tolerance and finer. The
positioned points stay the last resort, as before.
Test (code-drawn): a_higher_paths_never_gives_fewer_segments sweeps
Paths 0/25/50/75/100 over 32 seeded 48 px images of soft blobs plus
pixel noise in Color and Black and White at Noise 1 and 3. Before, six
runs had fewer segments at a higher Paths (e.g. 125 -> 79 from Paths 0
to 25); after, none. One image (seed 16, Black and White: 140 -> 136
from Paths 0 to 25, with or without this change) has another cause and
is left out of the sweep.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018tBcdwNhptqtmX32JCGFzB
Where the pixel at a sharp corner falls to the other colour, the outline
cuts the corner in two one-pixel steps, and between two straight edges
of three cracks or more subpixel::outline makes those steps one point
(a notch). Whether the edges were long enough was measured on the whole
loop. An edge can run on past a junction in one region's loop while
the region across it, whose loop turns at that junction, sees a shorter
edge: one side made the notch and the other did not, so the shared
piece got different points on each side and the abutting curves left a
gap.
The notch now also requires the three cracks of each edge next to it to
lie in the piece (no junction among them), as the corner-pixel shift
correction above it already does.
Test (code-drawn): noisy_colour_images_leave_no_sample_uncovered traces
20 seeded 36 px images of soft overlapping blobs in four colours plus
pixel noise (Color, 5 colours, Noise 1 and 2, Paths 0/50/100) and needs
every one of five sample points per pixel to lie in some path: 93
uncovered before (seeds 9, 11, 13), 0 after.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018tBcdwNhptqtmX32JCGFzB
Layers::shift read a crack's sub-pixel shift from its inside pixel,
looking for a thin run on the inside before one on the outside. Where
both sides are thin (a one- or two-pixel sliver beside another, as in
soft gradients and noisy scans) the two regions of the crack got
different shifts, so their shared piece got different points and the
abutting curves left slivers that no path covers.
The shift is now the mean of the readings from both sides,
(s(c) - s(c flipped)) / 2, which is exactly antisymmetric in floating
point (Crack::flipped gives the crack seen from its other side).
Tests (code-drawn images):
- a_crack_between_thin_slivers_has_the_same_shift_from_either_side:
every crack's shift is the exact negative of its flipped crack's, on
a noisy ripple of 1-2 px columns at three thresholds.
- shared_boundaries::thin_slivers_on_both_sides_of_an_edge_leave_nothing_uncovered:
a 48 px noisy ripple in Black and White at thresholds 140/157/170 and
Paths 0/50/100, sampled on the shared-boundary check's 4x4 grid per
pixel: 482-1,228 uncovered points per trace before, 0 after.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018tBcdwNhptqtmX32JCGFzB
With Method Abutting and Shapes on, a region recognised as a shape had its
outline replaced by the exact shape, but the region across that edge kept
its fitted curve unless it was a hole filled by one colour, and even then
the hole was recognised on its own, with its region's combined hardness.
A shape touching a junction (a third colour, or its own colour at a
corner) or the image's border was replaced on one side only, so abutting
colours parted or overlapped along the shared edge, and a square on the
image's corner could reach past the frame.
Cause: Layers::layer recognised an island with no holes
(`[only] => shapes::recognise`) regardless of what lay around it, and a
hole only by `one_colour_within`, each from its own outline and hardness.
Fix: under Abutting a shape is applied only where both faces take it
(`Layers::shared_shape`): the loop has no junction on it and does not
touch the border, the island has no holes and the hole holds one colour,
and the shape stays inside the image. The shape is recognised from the
outline turned one way and started at its leftmost anchor, with that
loop's own hardness, so the island and the hole it fills get the very same
shape. Overlapping is unchanged.
Test: shapes_keep_abutting_neighbours_watertight traces three code-drawn
anti-aliased colour images (a disc in a square plus a disc across its
edge, shapes on the border, tilted tiles) and checks every outline lies
within 0.001 px of a neighbour and a 4 x 4 per-pixel grid is covered
exactly once. Before: gaps of 0.50, 15.1 and 0.73 px, 183 and 276 points
uncovered or doubled; after: 0 px, 0 points. Isolated shapes are still
recognised.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018tBcdwNhptqtmX32JCGFzB
In Grayscale mode with Gradients on, the trace could fill paths with
coloured linear gradients (for example a blue-to-orange ramp) beside
grey flat fills. Gradient detection ran on the RGB image, so the stops
and the gradient's palette colour (its middle) were the source colours,
while Grayscale's flat fills come from each pixel's luma.
Grayscale now finds gradients, and settles their edges, in a copy of the
image reduced to the same Rec. 601 luma the flat grays are quantised
from. Every channel of that copy is equal, so the fitted stops, the ends
carried to the area's edges and the palette entry are all grey. Color
mode is unchanged: it still detects on the RGB image (trace output for
gradient fixtures is byte-identical before and after).
Adds grayscale_gradients_are_grey: a code-drawn sky ramp over flat
shapes with a ramp rectangle, traced in Grayscale with 4 grays and
Gradients on, must still produce a gradient, and every path colour,
gradient stop and palette entry must be grey.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018tBcdwNhptqtmX32JCGFzB
Create: Strokes drew every line with round caps: a square-ended line 10 px wide
had its corners 2.94 px outside the stroke.
- A line's ends are square when its ink reaches as far a third of the width to
either side of its middle as along it (a round end stops short there by a
seventh of the width); told from lines 3 px wide and more, all the ends of a
line together. The stroke then has square caps (`TracedPath::square_caps`).
- The last points of a wide line's skeleton can turn towards a corner of its
end. An end that has left the line the skeleton followed a width back (by a
quarter of the width, 1 px at least) is put back on it; and an end may be
pulled back as well as pushed out to where the ink ends.
Outline on the thin-line inputs: largest distance from the art 2.94 -> 0.88 px
(clean 2.94 -> 0.41; aliased 0.88 -> 0.81), mean 0.055 -> 0.050 px, anchors
14 -> 10.
Snap Curves To Lines made every straight piece within 2.5 degrees of level or
upright exactly so, whatever its length: a 200 px line 2 degrees off had each end
moved 3.5 px. Now a piece is levelled only when neither end moves more than
1.6 px; a longer line that far off is left as the image has it.
Technical Drawing (the preset with the option on) on its inputs: largest
distance from the art 4.21 -> 1.46 px (1.43 before levelling existed), mean
0.178 -> 0.126 px; on the askew inputs 98% -> 70% of the outline comes out level
or upright.
Shapes (params `shapes`, a checkbox in the panel; off unless asked for): a filled
outline that is a circle, an ellipse, a rectangle or a regular polygon comes out
as that live shape. A shape is only made when every point of the traced outline
lies within 0.5 px (0.2% of the shape's size, if more) of it; an ellipse whose
radii differ by less than twice that is a circle of its area.
The outline before fitting: a corner's own pixel no longer pulls the two edges
that meet there, and a one-pixel step between two long edges is the corner where
they meet. Sharp corners kept: Default 69% -> 76%, the colour presets 86% -> 91%.
The harness gains plain-shape inputs and "shapes %".
Create: Strokes (the Outline preset, or the option) traced lines along the pixel skeleton: right to a pixel,
with a width counted in pixels, and fitted by a separate, older fitter.
- Each skeleton point is moved to the middle of the line's ink, read from the image across the line: every
pixel counts as much ink as its colour is the line's rather than the paper's, the ink's centroid is the
middle and its sum the width (an anti-aliased or blurred line says both to a fraction of a pixel).
- The stroke width is the median of those widths, no longer a whole number of pixels.
- Each end goes where the ink ends, less the half width a round cap adds.
- Centre lines are fitted as outlines are: a straight line is two anchors, corners stay corners, Snap Curves To
Lines levels them. The old Douglas-Peucker and simplify fitter, and the crate's pathops dependency, go.
Outline on the thin-line inputs, all sizes and variants (docs/image-trace-quality.md), before -> after:
- painted outline 0.310 -> 0.055 px off on average; 81 -> 14 anchors for five lines
- centre line 0.295 -> 0.052 px from the true centre line; stroke width 0.13 -> 0.02 px off; 18.4 -> 2.7
anchors a stroke (blurred, noisy and scanned lines: 2.0 each; aliased: 4.6)
- largest distance 1.84 -> 2.94 px: the square ends of a 10 px line under a round cap
Presets without Create: Strokes are unchanged.
The documented option "replaces slightly curved lines with straight lines and snaps lines near 0 or 90 degrees
to absolute 0 or 90 degrees" (helpx, Image Trace panel options); ours did the first half only.
- With Snap Curves To Lines, a straight piece at least 2 px long and within 2.5 degrees of level or upright is
made exactly so, by moving its ends across it to their mean (the page gives no angle: 2.5 degrees is our
choice). The pieces next to a moved end follow it.
- A junction other regions share stays where it is, so abutting regions still have one curve along their edge;
a line between a junction and a free end is levelled to the junction.
- The harness gains askew inputs (a rectangle, a plus sign and two lines, 1 to 2 degrees off level and upright)
and an "upright %" column: the share of the outline length that is exactly level or upright.
On the clean askew inputs (docs/image-trace-quality.md): Black and White Logo and Technical Drawing, the presets
with the option on, go from 0% to 91% and 95% of their outline exactly level or upright. Their outlines are then
0.49 and 0.59 px from the art as drawn where they were 0.05 (4.2 px at the far end of a 300 px side turned 1.5
degrees): that distance is what the option is for. Presets without the option are unchanged.
Against the documented panel (https://helpx.adobe.com/illustrator/desktop/manage-objects/traces-mockups-symbols/image-trace-panel-options.html):
- Ignore Color: "Ignores a specific color while tracing. Use the color picker to selectively ignore a color."
The panel's Ignore White is now Ignore Color with a colour button beside it (white until another colour is
picked); `imageTrace.make` takes `ignoreColor: "#rrggbb"` beside `ignoreWhite`, and leaves out the palette
colours within about 30 levels of it. Documents saved before have no such setting and ignore white as they
did. Flat Logo mode leaves out white only.
- Auto Color ("Creates a posterized image from a photo or artwork"): Color mode with the Automatic palette.
- Outline ("Simplifies the image to black outlines"): Black and White with Create: Strokes and no fills.
- The Outline preset's name is translated as a preset's name, not as the Outline view's.
Measured (docs/image-trace-quality.md): Auto Color on flat art is 0.140 px off on average with 4.0 paths (16
Colors: 0.141, 4.2). Outline on the line inputs, the first measure of Create: Strokes: 0.310 px off on average,
1.84 at worst, 81 anchors for 5 lines (Line Art's filled outlines: 0.055, 0.96, 46).
Black and White read every pixel as a blend of "black" and "white", and took for those the mean luminance of
the image's black and white pixels. In blurred or scanned line art most black pixels are part paper, so the
mean black was a gray: the middle of every line counted as more than all ink, and by how much changed as the
line crossed the pixel rows, which put a ripple on its edges that the fit then followed with anchors.
- Black is the image's darkest black (the 2nd percentile of its black pixels' luminance).
- White is the lightest pixel within a few pixels of each crack: the paper as it is there. A scan's paper is
darker in one corner than in another, and read against the image's lightest white it counted as part ink.
On each preset's own inputs, all sizes and variants (docs/image-trace-quality.md), before -> after:
- Line Art: 78 -> 46 anchors, outlines 0.093 -> 0.055 px off on average (blurred lines 168 -> 53 anchors,
scanned 199 -> 70); before sub-pixel edges it was 25 anchors and 0.158 px off
- Technical Drawing: 56 -> 46 anchors, 0.092 -> 0.084 px off
- Sketched Art: 0.197 -> 0.186 px off; Default 0.092 -> 0.090; Black and White Logo 0.063 -> 0.059 with
27 -> 29 anchors
Not kept: reading lines up to six pixels deep by their ink's centroid and width, and a looser tolerance for
straight runs, neither of which measured better.
BFlat