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.
- 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 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.
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.
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.
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).