Every tool and command, what it actually does, and the behaviour that is easy to miss. Written against the shipping code — if something here is wrong, that is a bug in one of the two.
Thirteen rail buttons in three runs. Every one has a single-key shortcut, shown on hover and in the Tools menu.
| Tool | Behaviour | |
|---|---|---|
P |
Pencil | Always a hard 1px nib. Not size-aware on purpose — that is the promise of the tool; making it size-aware would make it a small brush. |
B |
Brush | Four tips at 1–96px. Round and square are hard-edged; soft antialiases over the outer ring; spray is the airbrush — it scatters coverage weighted to the centre and keeps spraying while you hold still, which is the whole feel of it. Flow sets density, and appears only for the spray tip. Seeded randomness, so a given engine sprays reproducibly. Spray used to be its own rail button; it is a nib, not a job. |
H |
Highlighter | A 4px floor, because the chisel nib clamps there: the size control shows what the stroke will be rather than a number the engine would round up. Arming it raises a smaller size to 4 and hands the old one back when you leave, so one highlighter stroke does not cost you the 1–3px sizes everywhere else. Coverage buffer, so overlapping passes within one stroke never darken. Drag back over your own line and it stays one flat tone, the way a real highlighter does. |
C |
Clone | Copy pixels from one part of the canvas to another, which is how you put back a chunk an AI generator left out. Click once to set the source, then drag where the pixels should go. The pairing is aligned: the offset holds across strokes, so you set it once and paint the hole in as many passes as it takes, and it survives until you pick a new source. Every destination reads the canvas as it was before the stroke started, so dragging back across your own source cannot turn the source into a copy of the hole. A source that falls outside the canvas is skipped rather than wrapped. Honours a selection, unlike the brush. |
F |
Soften | The same cell in its other mode, for hiding the seam a clone leaves. Blurs towards the neighbourhood as it was before the stroke, so holding still does nothing at all — the pixel you get after two hundred events is the pixel you got after one. That is what stops it being a smudge, and a smudge is what turns crisp artwork to mush. Strength runs 15–85%. |
E |
Eraser | Lays down the background colour — which is what makes it read as removing paint. Right-drag inverts that pairing. |
| Tool | Behaviour | |
|---|---|---|
U |
Shape | Fifteen kinds, below. Stroke weight, dash, fill/outline, corner radius, and Edges. A arms Shape with Arrow in one key. |
T |
Text | Drag a box and type in place, at the size and font it will land at. ⌘-drag moves the box while you type. ⌘↩ places it, ⎋ discards. Rasterises on commit. A click instead of a drag gets a one-line box pulled back inside the canvas, so clicking near an edge still gives you something usable. |
N |
Step badge | Click to drop 1, 2, 3… in the current colour, numeral auto-contrasted. Size follows the brush size. The options set the next number, so a run continued on a second screenshot can start at 4, and "Restart at 1" puts it back. |
K |
Fill | Scanline flood fill with a tolerance slider (0–32, per channel). A sweep on a real screenshot found coverage stable from 8 through 32, then a cliff at 48 where a probe in dark window chrome went from 4% to 91%. The slider stops at 32 because that is the last value the sweep covered. The engine still accepts 0–255. Explicitly iterative — a recursive fill overflows the stack on any realistic canvas. Filling with the colour already there is a no-op rather than an infinite loop. |
I |
Eyedropper | Samples into Colour 1. Hold ⌥ with any tool to do the same without switching — right-button samples into Colour 2. Never enters undo: a colour pick on the undo stack is a classic way to make ⌘Z feel broken. |
| Tool | Behaviour | |
|---|---|---|
M |
Select | Four modes in its options: rectangle, ellipse, lasso, Instant Alpha. Instant Alpha selects a connected colour without changing pixels; set tolerance, ⇧-click to add, ⌥-click to subtract, then choose Make transparent. Its marching ants follow the actual pixel mask rather than its bounds. |
R |
Pixelate | Mosaic effect. Averages each block to one value for visual obscuring, with a block size of 4–48. This is not secure redaction; use an opaque filled shape for secrets. |
S |
Spotlight | Drag a box and everything outside it dims, so the eye lands where you meant it to. Dim runs 10–90% and defaults to 45%, which leaves the surrounding UI readable as context. The corners are rounded by 10px. It scales the colour channels rather than compositing black over them, so alpha survives: veiling the outside would paint across the checkerboard on anything whose background you had already removed. Drags under 8px on either side do nothing, because a stray click would otherwise dim the entire image. |
Dragging inside an existing marquee lifts it and moves it, with no separate Cut step. Requiring Cut first is the classic reason people conclude a selection "doesn't do anything". Lifted content backfills with Colour 2.
Transparency is shown over a checkerboard on the canvas, so Instant Alpha's result is visible before save rather than inferred from a white background.
While content floats: drag to move, arrow keys to nudge one pixel, corner and
edge handles to resize (⇧ for uniform), ↩ to land it, ⎋ to discard. It keeps
its original pixels and re-renders on resize, so scaling down and back up does
not accumulate resampling loss.
Fifteen kinds inside the Shape tool, chosen from its gallery — which also arms
the tool, so it is a way in rather than a setting you can only reach once you
are already there. ⌥1–⌥9 pick the first nine.
Line · Curve · Arrow · Rectangle · Rounded rectangle · Ellipse · Triangle · Right triangle · Diamond · Pentagon · Hexagon · Five-point star · Six-point star · Speech bubble · Polygon
- Curve is two steps: drag the chord, release, then drag to bend it. The bend point is a point the curve actually passes through, not an off-curve control handle — dragging a handle the line never touches is why Bézier editors need explaining and this one does not.
- Polygon collects corners on each click and closes when you click the first
one again (or press
↩). Fewer than three corners is treated as a stray click and leaves nothing behind. - Both are pending until they finish: their pixels are on the canvas as a live
preview with no undo step, so
⎋leaves no trace and finishing records exactly one edit. Anything else you do lands them rather than dropping them. - Speech bubble leaves a gap in its outline where the tail meets the body, so it reads as one shape rather than a box with a triangle stuck on.
- The regular shapes (triangle through six-point star) come from one parametric generator sampled on the ellipse inscribed in the drag rect, so they stretch with the drag instead of staying stubbornly regular in a box that is not square.
Edges are antialiased by default. An outline is rendered by coverage rather than by stamping a nib along a Bresenham walk, so a diagonal has no staircase and a corner where two segments meet composites instead of overstamping. Switching it to hard pixels gives every covered pixel full coverage and nothing in between, which is what pixel art and nearest-neighbour scaling want. The pencil ignores the setting and is always hard, because that is the promise of the pencil.
Every outline can be solid, dashed or dotted, at any stroke weight; closed shapes can be outline, fill, or both.
- Outline uses Colour 1.
- Outline and fill uses Colour 1 for the edge and Colour 2 for the inside — the pairing the two loaded colours exist for.
- Fill uses Colour 1, because there is no edge to pair it with. It used to use Colour 2, which meant choosing Fill on a fresh document drew a white rectangle on white paper: the colour you had picked did nothing, and the shape was invisible.
Right-dragging swaps the pair, like everywhere else.
Hold ⇧ while dragging to constrain: lines snap to 45°, boxes and ellipses to
squares and circles.
- Colour 1 / Colour 2, overlapped in the rail. Click either for the system
picker;
Xswaps them. - The palette, always visible, two swatches across the rail. The bottom bar shows all 28; the narrower side rail shows the leading 14, truncated by column so every swatch keeps its place. Click for Colour 1, right-click for Colour 2.
- Colours you pick that are not in the palette land in a recent run in the popover, so the fixed 28 never move and the toolbar never changes height.
⇧⌘Copens the fuller swatch popover with hex read-outs and "Other colour…".
| Zoom | ⌘+ / ⌘− step the ramp (25% → 1600%); pinch and ⌘-scroll are continuous and anchored at the pointer; ⌘0 actual size; ⌘9 fit. |
| Pan | Hold Space and drag, with any tool. |
| Pixel grid | ⌘', shown once a pixel is comfortably bigger than the line that draws it (4× and above). |
| Footprint ring | Follows the pointer for every marking tool, showing exactly which pixels the next stroke covers. Past 4×, the single pixel under the pointer is outlined. |
| Toolbar position | ⌥⌘T moves the rail between left and bottom; remembered across launches. |
| Escape | Abandons whatever is in flight: stroke, pending shape, text box, floating paste, selection, options panel. |
Flip horizontal / vertical, rotate 90° either way or 180°, invert colours
(honours the selection — inverting one region is far more often what you want
on a screenshot), clear image, remove background, image size (⌘R), crop to
selection (⌘K), trim borders (⇧⌘T).
-
Crop to a lasso crops to the traced shape, clearing everything outside it to transparent — cropping to a freeform shape has to mean the shape, not the box around it.
-
Trim borders is tolerant by default (6/255 per channel): a screenshot's "solid" border is rarely one exact colour after a lossy format or a shadow, and a zero-tolerance trim silently does nothing on exactly the images people most want to trim.
-
Remove Background keys the page out from behind the subject in one command — the same flood Instant Alpha uses, seeded automatically at the four corners rather than by hand. Four corners, not one, because a subject that touches an edge splits the page into separate regions. An enclosed light area inside the subject is left alone: the flood is connected, and a hole in the middle of the artwork is not background.
It declines rather than guessing when the edges are all one region with the middle — on a flat image, removing the background would erase the picture — and says so, pointing at Instant Alpha for the version you steer yourself.
-
A size change clears undo history, because patches are addressed in canvas coordinates and would restore pixels into the wrong places.
⌘Vpastes as movable floating content, centred (or at the selection's origin).⇧⌘Vpastes and fits — growing the canvas rather than silently cropping a screenshot bigger than it.- Dropping an image from Finder, a browser or any app lands it at the pointer, growing the canvas if needed and clamping so it can never land entirely off-canvas.
⌥⌘Ccopies the whole image; Share… opens the system share sheet.- Pasteboard reads prefer the raw file or PNG data over
NSImage, whose representation can arrive scaled or DPI-adjusted.
The signature button in the header — or ⌃⌘S, or Tools ▸ Signature… — opens
the signing sheet. Sign in the box, or Import Image… a photo or scan of a
signature on paper. Saved signatures appear as chips at the top of the sheet;
clicking one inserts it, and right-clicking offers Delete.
The point of it is a PDF: open the contract, sign the page, save it back as a PDF. See Files and export below for what happens to the pages you did not touch.
- The ink is keyed to transparent, so a signature lands on artwork without a white rectangle behind it. Alpha comes from how dark each pixel is relative to its own local paper level, estimated per tile and interpolated, which is what survives the lighting gradient across a phone photo. Stroke ends stay soft rather than stair-stepping.
- It arrives floating, at most 40% of the canvas and inset from the lower-right. A signature never grows the canvas — that is the difference between signing something and pasting something.
- The ink takes Colour 1, so a blue-ink signature is one swatch away. A light Colour 1 falls back to black rather than saving invisible ink.
- A photo that is nearly blank, or nearly all dark, is reported rather than keyed — "no signature found" beats handing back a rectangle of noise.
- Signatures live as one PNG each in Application Support and are shared by every document. They are not document state: you capture one once and stamp it on everything you sign.
No camera capture yet — that needs a camera entitlement. AirDrop a photo from a phone and use Import Image…
Documents save as .itspaint: a package holding a lossless canvas.png plus
document.json (size, both colours, palette). Autosave-in-place applies to these
only — an imported PNG is your file and is never re-encoded in the background.
Export (⇧⌘E) offers format and scale in the save panel:
| Format | Notes |
|---|---|
| PNG, TIFF, GIF | lossless, alpha preserved |
| JPEG, BMP | no alpha — flattened onto Colour 2 first, rather than turning transparency black |
| HEIC, AVIF | modern, lossy, quality slider |
| a page, not a picture — see below | |
| ICO | fitted and centred into the nearest legal icon square (16–256); a non-square ICO is not a large icon, it is an invalid file |
The format list is filtered by what this machine's ImageIO can actually encode, so it never offers something that will fail at the last step. No WebP: macOS reads it but ships no encoder. PDF is the exception to that filter: Core Graphics' own PDF context writes it, not an ImageIO encoder.
PDF is paper. Opening one rasterises the page at 144 dpi so it can be drawn on — a signature, a correction, a circle round the clause that matters — and keeps the file it came from. Saving writes the edited page back into that document at its original size in points, and copies every page nobody touched through as itself, text and all. Multi-page documents get a page control at the bottom of the window; turning a page folds the current one back into the file first, and clears the undo stack, because an undo belongs to the page it was made on. A canvas that never came from a PDF still exports as a single page, one point per pixel.
- Tools — every tool by name with its key, a Shape submenu with all fifteen shapes, plus Signature…, Swap Colours and Larger / Smaller Brush.
- View — zoom commands, pixel grid, Move Toolbar, Colours…
- Edit — the usual, plus Invert Selection, Crop to Selection, Trim Borders, Swap Colours.
- Right-click on the canvas — cut, copy, paste, delete, select all, deselect,
crop, trim, copy whole image, export, swap colours, image size. A right-click
that drags paints Colour 2 instead;
⌃-click always opens the menu.
Every menu item routes through the responder chain, so it is enabled only when something can actually perform it.