One of our photographers lost his raw files from a photoshoot, but we still have the Capture One preview/proxy files (.CR2.cop) and I'm trying to find a way to extract image data from them to salvage the shoot.

I have read that they are JPGs, and I see evidence in the files (viewed with a hex editor) that they may be TIFFs – perhaps JPG-compressed TIFFs. Without success, I have tried (on copies):

  • changing file extensions
  • splicing and dicing blindly in the hex editor
  • "recovering" with Photorec (may not have done it properly)
  • opening the session in a fresh install of Capture One (nothing appears)
  • opening the proxy files directly in Capture One (nothing happens)

Can anyone shed light on the format of these files and/or how to open/display them?

I do have a request in to Phase One support to see if they can convert them for us. I've had one reply indicating "Normally it is not possible to convert preview files to jpegs," but they are passing it up the chain to see if something can be done.


For posterity, here's the ultimate solution we found.

  • Download trial version of Capture One.

  • Build a new session with dummy raw files (just the same JPG duplicated over and over) – the same number as in the failed session. Close the program.

  • Batch-rename (copies of) the failed session's proxy and settings files to match the equivalent files in the new dummy session. This consists of three files per photo: two (.cof, .cop) under CaptureOne > Cache > Proxies, and one (.cos) under CaptureOne > Settings70.

  • Transplant the renamed proxy and settings files into the dummy session, replacing the files already there. At this point, the dummy session will open in C1 and display the preview files from the failed session (albeit unstable – some preview files failed to display correctly, and C1 occasionally crashed – this may be a result of corruption in the original files).

  • Now it's a matter of saving them out in a usable format, which we did via screenshots. The preview files (per the preferences on the original C1 computer) had a resolution of 2560x1707. We were using a graphics card (NVIDIA) that allows creation of arbitrary resolutions, so we set the resolution to 2560x1707. The monitor wouldn't display this, so we used remote desktop software to view the display on another machine.

  • Step through and screenshot all the horizontal images, then invert the screen resolution to 1707x2560 and screenshot all the vertical ones.

It's not a "true" solution since we didn't find a way to open the proxy files directly, but we were able to retrieve the data with a minimum of data loss.


I believe Capture One v7 can open/view/edit the proxies without the original images present.

It may be possible to export ("process") the files to JPG or TIFF using only the previews, but obviously it will be limited to the quality and size of the preview images.

There's a 30 day free trial of C1 on their website. Might be worth a try to download it and try opening them.

  • Thank you for your reply! I have installed C1 and am trying it out. Do you mean to suggest opening the session, expecting the proxies to appear in it, or opening the proxies directly? I haven't had success with either approach yet. – Luke M May 30 '14 at 17:37

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