Sprite Sheet Packers Compared — Size, Exact Pixels, Duplicates
Four free ways to pack a sprite sheet, run on the same five real CC0 frame sets with trim on and padding 2: CodeAndWeb's free web packer, the GAPTools texture packer, free-tex-packer's npm core 0.3.9, and the Studio's Pack & Export. Every one turns frames into a PNG and a data file. They differ in how big the sheet is, whether each frame comes back pixel for pixel, what happens to duplicate frames, and whether a page limit is respected.
Four free packers were run on the same five CC0 frame sets with trim on, padding 2 and max 4096: CodeAndWeb's free web packer, GAPTools, free-tex-packer's npm core 0.3.9 and Nerulio's Pack & Export. They differ less in the packing rule than in what they keep: two browser tools changed pixel colours on the way through a canvas, two stored every duplicate frame again, and one ignored the page limit. Nerulio made the smallest sheet on all five sets with rotation and on four of five without; free-tex-packer runs from a command line, which Nerulio cannot.
- Godot 4Verified· Godot 4.7.2
- Phaser 3 / 4Verified· Phaser 3.90 + 4.2
- PixiJS 8Verified· PixiJS 8.21
- Unity 6Verified· Unity 6000.5.3f1
- Aseprite JSONVerified· Phaser load.aseprite · PixiJS 8.21
- .asepriteVerified· Aseprite 1.3.18
- Spine / libGDXVerified· spine-canvas 4.2
- Starling / Sparrow XMLVerified· Phaser 4.2
- LÖVEVerified· LÖVE 11.5
- DefoldBuilt· Defold bob.jar 1.13.1
- GameMakerUNVERIFIED
- CSS spritesVerified· Chromium
- GIF / APNGDecoded· Pillow
What to compare in a packer
Sheet area: how much of the page is frames. Efficiency here is the sum of the frames' opaque bounding boxes divided by the page area, so 0.84 means 16 % of the page is padding or empty space. A long strip can have a small area but may not fit an engine's maximum texture size.
Exact pixels: each frame is cut back out of the sheet with its data (trim offsets, rotation) and compared with the source file pixel by pixel. A browser tool that draws frames through an image element and a 2D canvas can change colours: grey (50, 50, 50) came back as (46, 46, 46) on frames with gAMA/cHRM colour chunks, and soft edges moved by up to 10 levels through premultiplied alpha.
Behaviour at the edges of the task: identical frames stored once or every time, a maximum page size kept by spreading frames over pages or ignored, and whether the output was ever loaded by a game engine.
- Efficiency
- Opaque bounding-box area of all frames ÷ total page area.
- Exact
- Every frame restored from the atlas equals its source file, ignoring colour under fully transparent pixels.
- Alias / dedupe
- Identical frames stored once and referenced by several names.
Worked example: efficiency and exactness on the ninja set
Six frames of 40 × 29 px; the sum of their opaque bounding boxes is 1,591 px² (docs/STUDIO-PACK-H2H.md, 2026-09-23).
tool sheet area efficiency exact frames
Nerulio (rotation off) 38 × 50 1,900 0.84 6 / 6
Nerulio (rotation on) 33 × 57 1,881 0.85 6 / 6
GAPTools 64 × 36 2,304 0.69 0 / 6
free-tex-packer-core 0.3.9 129 × 20 2,580 0.62 6 / 6
CodeAndWeb free (no trim) 126 × 62 7,812 0.20 0 / 6
efficiency = 1,591 / area, e.g. 1,591 / 1,900 = 0.84On archer without rotation the order changes: free-tex-packer's 3037 × 540 strip (1,639,980 px²) is 0.3 % smaller than Nerulio's 1543 × 1066 page (1,644,838 px²).
What it does
- Smallest sheet on all five sets when rotation is allowed and on four of five without it. The exception is archer, where free-tex-packer's sheet was 0.3 % smaller as a 3037×540 strip.
- PNGs are decoded in JavaScript, never through a canvas, so a PNG with gAMA/cHRM colour chunks or soft alpha edges comes back unchanged — every frame of all five sets restored exactly.
- Identical frames are stored once after a byte check (18 ninja frames → 6 stored), and a maximum page size is kept by spreading frames over up to 64 pages.
- When an export needs a different setting — no rotation for Godot, one page for Aseprite JSON — it re-packs for that export and shows the change next to its button.
Four free packers on five CC0 frame sets
Width × height of the one sheet each tool made, trim on, padding 2, max 4096. The Studio column gives the sheet without rotation first, then with rotation.
| Nerulio Studio | CodeAndWeb free web packer | GAPTools | free-tex-packer-core 0.3.9 | |
|---|---|---|---|---|
| ninja (6 frames) | 38×50; rotated 33×57 | 126×62 (no trim) | 64×36 | 129×20 |
| archer (10 frames) | 1543×1066; rotated 1071×1526 | 1532×1668 | 1936×872 | 3037×540 (a strip) |
| samurai (60 frames) | 275×248; rotated 313×216 | 400×400 | 292×256 | 276×300 |
| toon (45 frames) | 631×591; rotated 587×592 | 784×780 | 760×496 | 3560×105 (a strip) |
| spaceshooter (294 frames) | 966×977; rotated 944×996 | 1158×1051 | 1024×1024 | 1003×1003 |
| Sets restored pixel-exact | 5 of 5 | samurai only | samurai only | 5 of 5 |
| ninja ×3 (18 frames, 6 distinct) | 6 stored, 38×50 | 18 stored, 168×155 | 18 stored, 120×52 | 6 stored |
| archer ×8, max 2048 | 5 pages, 12,841,021 px²; dedupe on: 10 stored, one 1543×1066 page | one 4213×4448 sheet (limit ignored) | 5 sheets, 13,253,792 px² | — |
| Trim and rotation | none / trim / crop-keep / crop; rotation per engine | neither (paid Pro) | trim, rotation | trim, rotation |
| Runs as | browser, local | browser, local | browser, local | npm package (web app gone) |
| Output loaded by the engines | Godot, Unity, Phaser 3/4, PixiJS 8, Spine, LÖVE, Aseprite; Defold built | — | — | — |
Source of these numbers: docs/STUDIO-PACK-H2H.md (2026-09-23)
Where free-tex-packer / GAPTools / CodeAndWeb is the better choice
- free-tex-packer's core is an npm package with a command line, so it runs inside a build script; the Studio has no command line. Its OptimalPacker was also 0.3 % smaller on archer without rotation (as a strip).
- GAPTools and CodeAndWeb's free packer are a single web page: add frames, press pack, done — quicker for a one-off sheet than opening a project.
- CodeAndWeb's paid TexturePacker Pro goes past every free tool here: polygon packing, GPU texture formats and a command line with smart folders. The Studio packs rectangles only.
How to do it
- Drop the frames — numbered PNGs, a folder, a GIF or an .aseprite — on this page; they open in Sprite and go on to Pack & Export.
- Set trim on, padding 2 and a max size to repeat this test with your own art.
- Raise the effort to best and compare the used % and the page tabs with what your current packer gives.
- Export for your engine, or as Generic JSON (a TexturePacker-style hash) for any loader that reads that.
Other ways to do it
| Option | When it is the better choice |
|---|---|
| free-tex-packer (npm core 0.3.9) | You pack in a build script or CI: it is a Node package with a command line, its frames came back exact and duplicates were stored once. Its web app is gone. |
| GAPTools or CodeAndWeb's free web packer | A one-off sheet from a single web page when exact colours do not matter; both restored only the samurai set exactly, and CodeAndWeb's free version does not trim or rotate. |
| TexturePacker Pro (paid) | Polygon packing, GPU texture formats, 68 data formats and a command line; measured against Nerulio on the TexturePacker comparison. |
| Aseprite's packed sheet export | The art is in Aseprite and one page with tags is enough: --sheet-pack with --trim and --merge-duplicates. It was not part of this measurement. |
| Nerulio Pack & Export | Frames must stay exact, duplicates merged and a page limit kept, and the result should load straight into an engine: sprite sheet maker. |
Engine exports and how each was checked
"Verified" means the exported files were loaded by the real engine or tool on real CC0 assets and the result was compared with the source. Anything that was not loaded is labelled as such.
| Target | Files | Check |
|---|---|---|
| Godot 4 | .tres SpriteFrames · .tscn AnimatedSprite2D · .png.import | Verified Godot 4.7.2Loaded by Godot; every animation frame drawn and compared with the source file. The scene uses Nearest filtering; rotation is never used. |
| Unity 6 | .unity.json · Editor/NerulioSpriteImporter.cs · AnimationClip | Verified Unity 6000.5.3f1Batch mode: sprite rects, pivots, pixels, clip keys and durations checked. |
| Phaser 3 / 4 | atlas JSON (multiatlas) · .anims.json | Verified Phaser 3.90 + 4.2Frames and animations drawn by both versions. |
| PixiJS 8 | spritesheet JSON · animations · anchor · meta.scale | Verified PixiJS 8.21Rotated and multi-page atlases included. |
| Aseprite JSON | hash / array · frameTags · slices | Verified Phaser load.aseprite · PixiJS 8.21Tags keep their direction and repeat count. |
| .aseprite | layers · tags · durations · slices | Verified Aseprite 1.3.18Opened and rendered by the Aseprite command line. |
| Spine / libGDX | .atlas | Verified spine-canvas 4.2Every region drawn by the Spine runtime, rotated and trimmed; libGDX itself was not run. |
| Starling / Sparrow XML | XML per page | Verified Phaser 4.2Phaser 3.90 draws trimmed XML frames wrongly (its own bug); the "Sparrow XML (Phaser 3)" preset turns trim off and passes in 3.90 and 4.2. |
| LÖVE | Lua quads · nerulio_atlas.lua · main.lua | Verified LÖVE 11.5Every frame drawn and every animation stepped through the shipped helper. |
| Defold | .atlas · .tilesource | Built Defold bob.jar 1.13.1Built by Defold's command-line builder; the built texture's UVs were read back. |
| GameMaker | spr_<name>_stripN.png · gamemaker.json | UNVERIFIEDNot loaded in GameMaker (no headless GameMaker). The strips are cut the way its strip importer cuts them. |
| CSS sprites | .css · preview .html | Verified ChromiumEvery class drawn from the shipped stylesheet. |
| GIF / APNG | one file per animation | Decoded PillowEvery frame and delay decoded again after export; APNG is exact. |
Evidence
Exports: 49 runs in the real engines on real CC0 assets, 47 pass — the 2 failures are Phaser 3.90's trimmed-XML bug, which the Phaser 3 preset avoids. Packer head-to-head on 5 real frame sets (CodeAndWeb free web packer, GAPTools, free-tex-packer): smallest sheet on all 5 with rotation allowed, 4 of 5 without; every frame restored pixel-exact.
What Nerulio lacks in this comparison
- No command line or npm package: packing needs the browser.
- On archer without rotation, free-tex-packer's sheet was 0.3 % smaller (as a 3037 × 540 strip).
- Rectangles only; no polygon packing.
- Pack time was not compared between tools; only Nerulio's own times were measured (2–60 ms per set in Node, spaceshooter 0.42 s).
- The web tools were measured as they were on 2026-09-23; they change without version numbers.
Limits
- Polygon (mesh) packing is not offered: none of the verified engines draws a mesh atlas from exported data.
- GameMaker strips are UNVERIFIED in GameMaker itself.
- Scale variants (@0.5x–@4x) use nearest-neighbour only.
- Trimmed Starling XML is drawn wrongly by Phaser 3.90; use the "Sparrow XML (Phaser 3)" preset there.
Versions and sources
Measured on 2026-09-23: CodeAndWeb's free web packer and GAPTools live through Playwright, free-tex-packer-core 0.3.9 from npm, and Nerulio with the modules the Studio runs. The judge restored every frame with TexturePacker-JSON rules. Nerulio's exports were loaded in Godot 4.7.2, Unity 6000.5.3f1, Phaser 3.90 and 4.2, PixiJS 8.21, spine-canvas 4.2 and LÖVE 11.5; Defold bob.jar 1.13.1 built the Defold files.
Official documentation used
Questions
Why does a web packer change the colours of my frames?
The browser tools in this test decode through an <img> and a 2D canvas. Colour management turned grey (50,50,50) into (46,46,46) on the ninja frames, which carry gAMA/cHRM chunks, and premultiplied alpha moved soft edges by up to 10 levels on the space shooter set.
What happened to free-tex-packer?
Its web app's domain no longer hosts the app. The npm core (0.3.9) still works, and that is what was measured here: exact frames, duplicates stored once, and the one sheet that beat the Studio (archer, without rotation).
How was "restored exactly" checked?
Each frame was cut back out of the atlas using its data file (trim offsets, rotation) with TexturePacker JSON rules and compared with the source file pixel for pixel, ignoring colour under fully transparent pixels.
Is it free, and do I need an account?
Everything on these pages is free and works without an account. There is no watermark and no export that is held back.
Are my sprites uploaded?
No. The Studio decodes, packs and exports in this browser tab. Projects are autosaved in the browser (IndexedDB) and can be saved as a .nerulio file.
Does it need Aseprite or an engine plugin installed?
No. .aseprite files are read and written in the browser, and each engine bundle carries what that engine needs (for Godot, the import settings and scene; for Unity and the Godot TileSet, a small editor script).