The .cls project file
What a Celas Studio project holds, what it stores inside the file, what it only points to, and what it cannot be converted into.
A Celas Studio project is a single file with a .cls extension. It holds the whole scene: every layer, keyframe, bone, action, symbol and cell, along with the canvas size, frame rate, frame count and the playback settings you set in Project Settings.
Inside, a .cls is an archive with a few entries: a description of the scene, a small preview image, and an assets folder holding the artwork that had to travel with the project. You never work with those parts directly, but knowing what goes in explains why one project is a few hundred kilobytes and another is two hundred megabytes.
What travels inside the file
Anything you painted or drew in Celas Studio is stored in the project itself, and so is any still image you imported.
- Shape layers, groups, bones, mesh cages, weights, vertex welds and the symbol library
- Every keyframe and sub-track, actions, tags and markers, and the scene palette
- Raster drawing cells, one lossless image per cell
- A Pixel layer's bitmap, again lossless
- Imported images and Photoshop layers, kept as the original file bytes
- Per-layer switches such as alpha lock, and the full fill description of a gradient: its stop midpoints, its second radius, its angle and how it extends past its ends
Raster cells and Pixel layers are written losslessly, so a project survives any number of save-and-reopen rounds with the pixels untouched, including the colour that sits underneath fully transparent pixels, which is what a smudge or a soft eraser leaves behind.
What is only linked
Video and audio are the exception: the project stores the file path, the clip layout and the trims, never the media itself. A one-minute video adds only a few kilobytes to your .cls, and the layer keeps working as long as the file stays where it was.
The preview thumbnail
Every save renders the current frame into a small preview and stores it in the project. It is capped at 360 pixels on its long edge and drawn without selection handles or gizmos, so it shows the artwork rather than the editing state.
That preview is what you see on the cards in the Home window's Recent tab. It is refreshed on every save, so the card always shows the frame you were parked on when you last saved.
Why the same project can differ in size
The scene description is compressed in the released build. Development builds write it uncompressed so a crash leaves something readable, which can make the very same scene noticeably larger there. Either build opens either file, and the artwork is identical. Only the packing differs.
Beyond that, size follows what you drew. Vector work is tiny. Raster cells and Pixel layers are lossless, so a full-canvas painting costs roughly what a lossless image of that canvas costs, multiplied by the number of cells. Imported images are stored byte for byte, exactly as large as the files you brought in.
What .cls is not
There is no round trip to other formats. Photoshop and SVG files are read on the way in and converted into Celas Studio layers; nothing is written back to them, and saving never touches the file you imported from.
Celas Studio also does not write a .cls back out as a PSD, an SVG or any other editable document. Output means rendering: images, an image sequence, a sprite sheet, an animated GIF or a video, all covered under Exporting. If you want a copy of the project itself, use Save As.