A .CEL file has multiple possible meanings, so its explanation depends entirely on the software or field that produced it; in biotech/genomics it most often represents an Affymetrix/Thermo Fisher GeneChip microarray output that stores raw probe-intensity values from a scanned chip, where each tiny probe spot on the array is measured for brightness after hybridization, and the CEL file records those intensity readings—often indexed by X/Y grid location—along with scan metadata, forming "raw" data that still needs downstream steps like background correction, normalization, and probe summarization using tools such as R/Bioconductor’s oligo, plus companion files like .CDF and .CHP.

In animation and graphics, "cel" traces back to physical celluloid used in 2D animation, and a CEL file typically represents a single raster frame or layer—often transparent—stacked over backgrounds or other layers, usually appearing in sequences like `walk_001.cel` along with palette files or related images, though because different tools used different CEL variants, some open in standard editors while others require the original software or palette; meanwhile, certain games and niche apps also use `.CEL` as a custom sprite/texture container, so the extension alone can’t identify it, and the fastest way to figure out which type you have is by checking its origin, nearby files, naming patterns, size, and a quick look in a text/hex viewer to see whether it resembles microarray metadata or a binary art/game asset.

In 2D animation, a "cel" comes from the old method of layering drawings on cels to capture one moment of a character over a background, and digital techniques mimic this structure; in that context, a CEL file typically contains a raster layer or frame—maybe a pose, mouth shape, or effects sprite—with transparent areas enabling easy compositing with background and other layers.

Because ".CEL" appears in multiple software ecosystems, an animation CEL isn’t always a standardized image like PNG—it might be palette-based, stored in a tool-specific format, or rely on a separate palette file; that’s why CEL files often appear in art-pipeline folders (`frames`, `sprites`, `cels`, `anim`) or in sequences like `idle_001.cel`, and opening them can be easy in some editors or may require the original software or a converter, especially when colors depend on an external palette, with each CEL representing just one raster layer/frame rather than the entire animation.

To classify a .CEL file quickly, the most reliable move is to use context instead of guessing, since genomic sources typically point to microarray CELs, whereas art/game pipelines suggest animation layers or asset formats; look at nearby files for confirmation—microarray sets include .CDF or .CHP, while animation/game folders contain many numbered CELs and palette files—and then compare file size, count, and a small header peek in a text/hex viewer to spot either readable array metadata or primarily binary graphics/asset data.

".CEL isn’t a single universal standard" reflects that multiple industries repurposed the extension, leading to cases where Affymetrix CELs record raw intensity data, animation CELs hold raster cels or palette images, and game CELs pack proprietary resources, all under the same extension; because of that, identifying the correct flavor requires either context about its source or a look at file headers and related files.