DICOM file format: what it is and how to use it

DICOM is medicine's imaging standard: pixel data wrapped in hundreds of metadata tags about the patient, the study and the machine that took it. Learn when to use it and what to choose instead.

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What is a DICOM file?

A .dcm/.dicom file is a medical image in DICOM, Digital Imaging and Communications in Medicine, the NEMA standard behind every CT, MRI, X-ray and ultrasound scanner. Each file pairs the pixel data with a rich dataset of tagged elements: patient and study identifiers, modality, device settings, windowing parameters and sometimes whole image series. It is a database row as much as a picture.

When should you use DICOM?

  • Clinical imaging: the only format PACS systems, scanners and hospital workflows accept.
  • Series with context: windowing, slice positions and acquisition data stay attached.
  • Medical research: anonymized datasets preserve machine parameters scientists need.

When is another format a better fit?

For publications and presentations, export PNG or JPG, a flat image with the patient data stripped. For astronomical data the analogous role belongs to FITS. And for long-term image storage outside medicine, TIFF carries pixels without the clinical overhead.

The short version: DICOM is the imaging record of medicine: pixels plus their full clinical context. Convert out only for display.

How to open a DICOM file

On Windows

Double-click the file, or open it with RadiAnt Viewer.

On macOS

Horos/OsiriX opens DICOM files on macOS.

In your browser

Open DICOM files right in a browser tab or with the dexrr viewer. No install, no upload.

Also opens in

  • RadiAnt Viewer
  • Horos/OsiriX
  • MicroDicom
  • GIMP (plugin)

View or convert DICOM files

A quick preview or a new format. No install, no upload.

View DICOM files Preview and inspect DICOM files Convert to DICOM Turn files into DICOM DICOM to FITS Flexible Image Transport System DICOM to TIFF Tagged Image File Format DICOM to PNG Portable Network Graphics

DICOM technical details

Full name
Digital Imaging and Communications in Medicine
Extensions
.dcm .dicom
MIME type
application/dicom, image/dicom-rle
Magic bytes
44 49 43 4D (DICM, offset 128)
Compression
Lossless or lossy
Developer
NEMA / ACR
Specification
www.dicomstandard.org

DICOM questions, answered

How do I open a .dcm/.dicom file?

Medical viewers like RadiAnt, Horos, Weasis or MicroDicom read it; GIMP and ImageMagick handle many too. dexrr displays and converts dicom files in your browser. Nothing is uploaded, which matters for patient data.

Can I convert DICOM files online?

Yes, dexrr converts dicom locally in your browser to png or jpg for reports and presentations.

What is the difference between .dcm and .dicom?

Same format: .dcm is the common short extension, .dicom the spelled-out variant. Both are DICOM datasets.

Why does my DICOM look too dark or washed out?

It stores raw values plus windowing parameters. Apply the embedded window/level or auto-window in the viewer to see the intended contrast.

Is the DICOM format outdated?

No, it is the living international standard of medical imaging, continuously maintained and universally deployed.