Opening a .BAY file depends on whether you want speed or accuracy, and the best-quality workflow is through Lightroom or Adobe Camera Raw where the BAY is decoded, demosaiced, white-balanced, and color-profiled so you can adjust highlights, shadows, and color before exporting JPG/TIFF; if Adobe doesn’t open it, your Camera Raw likely lacks support for that specific Casio type, so RawTherapee or darktable—both known to handle unusual RAWs—are excellent alternatives, while quick viewers like XnView MP or IrfanView may only show embedded previews; converting to DNG can help but isn’t guaranteed, and when a BAY fails entirely, it’s usually unsupported encoding, corruption, or bad SD copies, so re-copying and testing another BAY plus trying RawTherapee is often the fix.

Where a .BAY file comes from is a key clue, because BAY is usually a Casio RAW photo but can also be a mislabeled or device-specific file, so if it came directly from a Casio Exilim SD card it’s almost certainly real RAW data that needs a proper editor like Lightroom, Camera Raw, RawTherapee, or darktable—while Windows Photos or simple viewers may fail or only show previews; but if it came from a phone app, CCTV, dashcam, downloader, or website, it might be non-photo, meaning the correct tool is whatever created it, and if it came from a backup/export/data-recovery set, it may be incomplete or missing sidecars like .THM or .JPG previews, causing errors or odd colors, so re-copying the original or checking for companion files helps, and overall the source determines whether to treat it as normal RAW (edit then export) or as a proprietary format needing its original software.

A .BAY file, when used as a Casio RAW image, holds the camera’s original capture arranged in a Bayer-pattern grid where each pixel site measures only red, green, or blue, so the file doesn’t contain a finished color image and must be demosaiced; it carries higher bit-depth data for better dynamic range and editing flexibility, plus metadata—camera model, shooting settings, white balance—that influence how RAW software starts its rendering, and it usually embeds a small JPEG preview that simple viewers show even though it may appear dull or inaccurate next to a true RAW interpretation.

A .BAY RAW file does not contain a complete RGB photo like JPG/PNG because the capture isn’t baked in yet; it keeps raw sensor readings plus metadata that merely guides how the image might be rendered, so there’s no definitive RGB pixel layout until demosaicing and color processing occur, and without those steps the image can appear dull or off-color, with any embedded preview JPEG serving only as a quick-view thumbnail rather than the real finished result.

When you open a .BAY file, the software builds the image from the sensor data instead of loading a completed picture, starting by decoding that Casio RAW flavor—which may differ by model—then demosaicing single-color photosite readings into RGB pixels, applying white balance and a profile-based color transform, and compressing the high-bit-depth range with a tone curve so the result looks normal rather than dull, usually adding noise reduction, sharpening, and sometimes lens-profile corrections, and what you see is just this processed preview; exporting to JPG/PNG/TIFF bakes in these choices, while unsupported variants yield errors, strange color, or only the embedded preview.