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KB 1721

Troubleshooting OpenCL

Last updated: 03-02-2021


I'm having problems with exporting/processing images; my images have artifacts in them when viewing/processing; processing/viewing images is slow. What's going on?



There are a few steps to troubleshoot OpenCL when performance is slow or when images are processed out with artifacts


The issues described in the title of this KB article are usually related to OpenCL. If you are unsure on what OpenCL is and how it works in Capture One, please see KB1720 on the link at the bottom

Whilst OpenCL is designed to increase performance in Capture One, you may find in some instances that it can decrease performance, or cause some issues when working on and processing images.

This is particularly important when working on machines which may not meet our recommended system requirements, which can be found in the release notes for the version of Capture One you are using.

Issues which may be related to OpenCL

- Scrambled or somewhat 'glitched' previews when making adjustments

- Crashes when processing/exporting images

- Artifacts in processed images

- Slow processing times

- Slow mask drawing

- Crash when opening Capture One

The first thing to do would be to see if the above issues disappear when setting OpenCL to 'Never'. This can be found in Preferences > General > Hardware Acceleration (Use OpenCL for)

If you have a machine which you consider to be 'high end' and meets our recommended system requirements, you may need to rebuild the kernels needed for OpenCL to initialise properly. This can be done by taking the following steps:

Rebuilding OpenCL kernels on Mac

Close Capture One and then delete the contents of this folder - however they may differ from the screenshot below - found in Macintosh HD/Users/Shared

When you restart Capture One, OpenCL will re-initialise.

Rebuilding OpenCL kernels on Windows

Just like the procedure on Mac, delete the contents of this folder - ignoring how the contents may differ - and restart Capture One, whereby OpenCL will re-initialise.

How can I tell if OpenCL is initialized?

  • Ensure that OpenCL is set to 'Auto' in your preferences
  • Reset adjustments on an image
  • Enable the focus mask by going to View > Show Focus Mask
  • Bring up the exposure slider gradually

If the focus mask disables while you are increasing your exposure, OpenCL is being utilized. If it remains visible while making these adjustments, then OpenCL has failed to initialize or is not in use.

Capture One Preferences will also show you when OpenCL is fully set up and in use

If Hardware Acceleration is stuck at 0% on initialization (Windows OS)

Its an access issue with Capture One enumerating installed OpenCL platforms. To Fix:

  • Close Capture One, then hold down the Windows key and push "r" on the keyboard
  • Type in "regedit" (without the quotes). This brings up the "Registry Editor"
  • Select "Yes" to make changes
  • From here go to: Computer\HKEY_Local_Machine\SOFTWARE\Khronos\OpenCL\Vendors
  • Right-click on IntelOpenCL64.dll and choose "Modify"
  • Enter 1 for Value. Leave Base alone

  • Then close out and restart the computer and Capture One
  • Hardware Acceleration on startup should initialize fully now.

Related Articles and Links:

KB1720: Capture One and OpenCL