COS File

What are COS files and how to open them

Are you having problems opening a COS file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your COS files.

What is a COS file?

COS files have multiple uses, and Capture One Settings/adjustment Info is one of them. Read more about the other uses further down the page.

Capture One Settings/adjustment Info

Capture One Settings/adjustment Info files store all the adjustments made to an image in Capture One. These files are created when an image is edited in a session, and they capture edits like exposure, white balance, lens correction, contrast, and other adjustments separately from the original RAW data so the edits can be changed or reset without altering the photo itself.

These adjustment-info files are produced by Phase One's Capture One software. In session-based workflows they are saved alongside the image files, inside a folder structure like …/CaptureOne/SettingsXX (where "XX" corresponds to the version of Capture One). Each image that has edits applied has a matching settings file with the same name as the image plus a settings file extension. The software reads that settings file to show the edited version of the photo whenever the RAW is viewed.

Because Capture One may also store edits in catalogs, some adjustment data are kept inside the catalog database; however many of the editing parameters and layer data are stored in individual settings files. Deleting these settings files causes those edits - particularly mask layers and other non-basic adjustments - to be lost or reset.

These files are in a proprietary binary format rather than a standard sidecar format like XMP. They encapsulate both simple edit values (such as EXPOSURE, WHITE BALANCE) and more complex data like adjustment curves, masks, lens corrections, chromatic aberration settings, and metadata about the image creation (camera model, firmware, etc.).

Technical signature data include an initial XML-like header sequence at the start (for example "<?xml version="1.0"?>"), followed by keywords such as LENSDIFFRACTIONCORRECTIONENABLED, GEOMETRYKEYSTONEFOCALLENGTH, COLORBALANCEMIDTONE, HIGHLIGHTRECOVERY, CAMERA_MODEL, IMAGE_DATECREATED, and many others.

How to open COS files

Important: Different programs may use files with the COS file extension for different purposes, so unless you are sure which format your COS file is, you may need to try a few different programs.

While we have not verified the apps ourselves yet, our users have suggested four different COS openers which you will find listed below.

Last updated: September 2, 2026

All known file formats using extension .COS

While Capture One Settings/adjustment Info is a popular type of COS-file, we know of 3 different uses of the .COS file extension. Different software may use files with the same extension for different types of data.

OMP Skin

OMP Skin is a theme package format used by Charamin OMP, a media player/3D character player that makes characters dance to music. The format stores graphics assets and user interface styling ("skin") that change how the Charamin OMP window looks - things like background images, colors, hover effects, and layout elements.

These skin files are created by the developers of Charamin OMP, or by content creators distributing custom skins for it. When Charamin OMP loads a skin, it applies the settings and assets stored in the file to draw its interface according to that design - things like button visuals, the window's appearance, and image overlays.

Internally, an OMP Skin file begins with the ASCII signature "OmpSkin" at file offset 0. It includes strings that refer to interface elements and layout options - SELECTED, ONIMAGE, BACKGR, DIMAGE, TCOLOR, HOVER - as well as entries suggesting embedded image data (.PNG) and references to PNG structure markers like IHDR, GAMA, IEND, and possibly IDAT.

WinArcadia Saved State

We know that one COS format is WinArcadia Saved State. We have not yet analyzed in detail what these files contain and what they are used for. We're working on it.

Various apps that use files with this extension

These apps are known to open certain types of COS files. Remember, different programs may use COS files for different purposes, so you may need to try out a few of them to be able to open your specific file.

Help us help others

File.org helps thousands of users every day, and we would love to hear from you if you have additional information about COS file formats, example files, or compatible programs. Please use the links below or email us at submit@file.org to discuss further.