CCP-EM

MRC File Format

MRC/CCP4 file format for images and volumes

The MRC format is widely used for image and volume data in cryoEM. It is closely related to the CCP4 map format for crystallography. Both originated from the MRC Laboratory of Molecular Biology, and the MRC format is now maintained by CCP-EM.

MRC2014

A major review of the MRC/CCP4 format was agreed in 2014. Details of the changes have been published in Cheng et al. (2015) “MRC2014: Extensions to the MRC format header for electron cryo-microscopy and tomography” (see also Short et al. 2023). Minor updates and clarifications have been made since then, formalised In January 2022 as update 20141.

See separate page for a detailed format specification.

MRC2000

The original MRC/CCP4 format was agreed between the crystallography and EM communities in 1982. An update to this format was agreed in 2000 to include a machine stamp in the file header, to aid file portability. This version is now obsolete, so please refer to the MRC2014 page for up-to-date information.

Future updates to the format

CCP-EM have undertaken to curate the MRC format on behalf of the EM community. The format is closely linked to the mrcfile software library and the MRC Image Processing package, both of which provide tools for working with MRC format files.

As part of the curation, we will look into possible future updates to the MRC/CCP4 format. The procedure will be:

  • Private concerns or suggestions for the format may be emailed to Martyn Winn.
  • Public discussions can take place on the CCP-EM mailing list.
  • Minor updates will be considered via lightweight discussion, and advertised on this updates page.
  • If the CCP-EM management committee consider that a serious issue/proposal has been raised, or if there has been an accumulation of small issues, we will convene a Change Committee to consider an update to the format. The committee will consist of representatives from at least 6 different institutions. It will be by invite only, but we welcome suggestions for membership.
  • If agreement can be reached, a draft format update will be advertised on the CCP-EM website, and interested parties invited to comment. We do not expect to achieve universal agreement, but will take note of any further issues raised.
  • Unless any major obstacles occur, the draft will be accepted 6 months after the issue/proposal was originally raised.