COMASK File

What are COMASK files and how to open them

Are you having problems opening a COMASK 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 COMASK files.

What is a COMASK file?

A .COMASK file is a Capture One Layer Mask file.

Capture One Layer Mask files store the masking information that belongs to adjustment layers created in Capture One's editing software. They are used whenever parts of an image are selectively adjusted - such as by brushing, gradients, or healing/cloning - without altering the original RAW or base image data. These files carry only the mask data; settings like exposure or color balance live elsewhere, attached to the adjustment layer rather than inside the mask files.

Capture One writes these files automatically when any local adjustment layer includes a mask. The mask enables non-destructive editing and can be edited, combined (add, subtract, intersect), inverted, or feathered inside Capture One. These mask files travel with the session or catalog's settings folder alongside other sidecar files so that mask shapes, opacity, and density are preserved even if you move or back up the project folder.

The format begins with a binary signature near the start identifying it as a Capture One mask file (containing strings like TYPE, CaptureOneMask, VER, XCON, MASKINFO, USERINFO). Some bytes at specific offsets (for example around offset 0 and offset 47) encode headers such as MaskInfo or Hdr.

How to open COMASK files

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

We have not yet verified any programs for Windows that work with this specific file format. If you know one, please use the 'Suggest a program' link below. Thanks!

Last updated: September 2, 2026

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