A .CEL file can represent distinct file types, though in microarray genomics it is most often the Affymetrix/Thermo Fisher format capturing raw probe-level brightness for one chip: the scanner reads each probe’s signal intensity and the CEL file logs these values plus metadata, still considered raw until processed using background correction, normalization, and summarization methods found in R/Bioconductor tools like affy, with structure guided by companion files including .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" originally meant a transparent painted sheet showing one slice of artwork placed over a background, and modern digital animation preserves the layered approach; a CEL file therefore acts as a raster image representing a single layer or frame—like an arm movement, facial expression, or effects element—with alpha transparency so it stacks seamlessly with other layers.

Because ".CEL" isn’t tied to one universal standard, an animation CEL may be an indexed-color image, a tool-specific frame, or part of a pipeline that expects a separate palette file; you’ll often see folders like `sprites`, `frames`, or `anim` containing sequences such as `walk_002.cel`, and depending on the variant, some viewers can open them while others require the original program, since the CEL is only one raster layer/frame that gets combined with others to form the final animation.

To tell what type of .CEL file you’re dealing with, the fastest method is to ignore the extension initially and examine origin: lab/genomics sources strongly indicate microarray CELs, animation workflows suggest layered image cels, and game directories point toward proprietary assets; neighbor files give more clues—.CDF/.CHP near microarray CELs, palette and frame files near animation/game cels—and file size, name patterns, plus a text/hex-view peek will quickly reveal either structured scan metadata or binary image/asset data.

".CEL isn’t a single universal standard" explains that the suffix doesn’t map to one agreed structure, because different companies and industries have reused ".cel" for unrelated purposes, treating it as a simple filename suffix rather than a format with a shared specification; that’s why an Affymetrix CEL can store probe-intensity data, an animation CEL can be a raster frame with transparency, and a game CEL can be a proprietary sprite/resource file—same extension but entirely different "languages" inside, making context or header inspection necessary to know which tool can open it.