Both DICOM and JPEG store images. Both can display a CT scan. But they are built for completely different purposes — one for clinical diagnosis, the other for screen display. Understanding the difference explains why hospitals don't just save scans as JPEGs.
Side-by-side comparison
| Property | DICOM | JPEG |
|---|---|---|
| Bit depth | Up to 16-bit grayscale | 8-bit |
| Compression | Lossless or uncompressed | Lossy (standard JPEG) |
| Metadata | Hundreds of patient/study tags | EXIF only (camera data) |
| Multi-frame | Yes (video/slice series) | No |
| Window/Level | Stored in header; adjustable | Baked into pixels |
| File size | Large (uncompressed) | Small (compressed) |
| Primary use | Clinical storage & diagnosis | Display, sharing, web |
| Software needed | DICOM viewer required | Any image viewer |
The critical difference: bit depth
A standard JPEG image has 256 shades of gray (8-bit). A CT scan stored as DICOM can have up to 65,536 shades of gray (16-bit). This matters enormously for diagnosis.
Bone, air, soft tissue, and blood all have distinct Hounsfield unit values on a CT scan. A 16-bit DICOM preserves all of these distinctions. An 8-bit JPEG collapses the full range into 256 bins — fine details between tissue types that are diagnostically significant can be lost.
This is why radiologists use Window/Level controls: they choose which slice of the 16-bit range to display. A "lung window" emphasizes air-filled structures; a "bone window" emphasizes calcified tissue. You cannot do this with a JPEG — the window is permanently baked in at export time.
When converting DICOM to JPEG is appropriate
Despite the limitations, converting DICOM to JPEG (or PNG) is common and appropriate in these situations:
- Case reports and publications — journal articles require standard image formats, not DICOM files
- Patient communication — sharing a scan with a patient who doesn't have a DICOM viewer
- Presentations — PowerPoint and Keynote don't accept DICOM natively
- AI/ML preprocessing — many image classification pipelines require standard formats
- De-identification — converting to JPEG removes the DICOM header entirely, stripping PHI metadata
In all these cases, you are making a deliberate trade: you lose clinical adjustability in exchange for compatibility and simplicity.
How to convert DICOM to JPEG without uploading
The 365tools DICOM Converter converts .dcm files to JPG, PNG, or WebP entirely in your browser — no upload, no PHI exposure:
- Go to the DICOM Converter
- Drop your .dcm file onto the upload zone
- Adjust Window/Level (lung, bone, brain, soft tissue presets available)
- Select JPG, PNG, or WebP output
- Download — no PHI in the output file
Convert DICOM to JPG/PNG — no upload, PHI-safe
Window/Level controls, multi-frame support, runs entirely in your browser.
Open DICOM Converter →Frequently asked questions
Can I use JPEG instead of DICOM for medical images?
For clinical storage and transmission, no — DICOM is required by hospital systems (PACS) and regulatory standards. JPEG loses the metadata and bit depth needed for diagnosis. For sharing or publishing non-clinical images (case reports, presentations), JPEG is acceptable.
Does converting DICOM to JPEG lose diagnostic information?
Yes. DICOM images can have up to 16-bit grayscale depth. JPEG is 8-bit. The conversion discards the extra bit depth and applies a specific window/level to map the 16-bit range to 8-bit. The resulting JPEG is a visual snapshot — it cannot be used for clinical window/level adjustment.
Is JPEG compression bad for medical images?
JPEG compression is considered inappropriate for primary diagnostic imaging because it introduces artifacts that can mimic or obscure pathology. Lossless formats (lossless JPEG 2000, PNG) are preferred when a non-DICOM format is required.
How do I convert DICOM to JPEG without uploading?
Use the 365tools DICOM Converter — it runs entirely in your browser and converts .dcm files to JPG, PNG, or WebP without sending your files to any server.