Open DICOM (.dcm) images from CT, MRI, X-ray and ultrasound right in your browser. Adjust window and level, zoom, step through multi-frame series, inspect every DICOM tag and save the view as PNG. Files are read locally and never uploaded.
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For viewing and education only. Not a medical device and not for diagnosis.
Window / level
Image
DICOM tags
Tag
VR
Name
Value
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How to use the DICOM Viewer
Open your file: click Choose files or drop .dcm files in the box. A synthetic CT phantom is shown until you do.
Adjust the contrast by dragging on the image: left and right change the window width, up and down move the level. Or pick a preset.
Navigate with the toolbar: switch to Pan to move the image, zoom with + and −, and use Fit to reset the view.
Scroll through frames of multi-frame files with the slider, the arrow keys or Play.
Inspect the tags in the table below the image, filter them, and export them as JSON. Press Download PNG to save the current view.
Common CT window settings
CT pixel values are measured in Hounsfield units (HU), where water is 0 and air is about −1000. The window determines which HU range is shown as shades of gray: values below center − width ÷ 2 are black and values above center + width ÷ 2 are white.
Preset
Center (level)
Width
Visible HU range
Typical use
Brain
40
80
0 to 80
Gray and white matter of the head
Soft tissue
40
400
−160 to 240
Chest and neck organs, muscle, fat
Abdomen
60
400
−140 to 260
Liver, kidneys, bowel
Lung
−600
1500
−1350 to 150
Air-filled lung tissue
Bone
400
1800
−500 to 1300
Skeleton and calcifications
Approximate Hounsfield values
Material
Approximate HU
Air
−1000
Lung tissue
−900 to −500
Fat
−120 to −60
Water
0
Soft tissue and blood
+20 to +80
Contrast-filled vessels
+150 to +400
Bone
+300 to +2000
The stored pixel value is turned into a real-world value with output = stored value × Rescale Slope + Rescale Intercept. Many CT scanners store HU + 1024 and use an intercept of −1024.
What is inside a DICOM file?
Preamble and signature: 128 bytes followed by the letters DICM. Files without them are raw datasets, which this viewer also tries to read.
File meta information (group 0002): says which transfer syntax (byte order and compression) the rest of the file uses.
Data elements: each has a tag such as (0010,0010) Patient Name, a value representation (VR) like PN, DA or US, and a value. Sequences (SQ) nest whole sets of elements.
Pixel data (7FE0,0010): the image itself, described by Rows, Columns, Bits Allocated, Bits Stored and Photometric Interpretation tags.
To check what kind of file you have before opening it, the Image Format Detector reads file signatures, and the Image Metadata Viewer shows EXIF data of ordinary photos.
Frequently asked questions
How do I open a DICOM file without installing software?
Choose or drop the .dcm file into the viewer above. The file is parsed by JavaScript in your browser, the image is drawn on a canvas and the tags are listed below it. Nothing is installed and nothing is uploaded. Files exported from CDs often have no extension at all; they open the same way.
What are window and level?
Medical images often store more than 4,000 gray values, but a screen can show only 256. The window width sets how wide a range of values is spread from black to white, and the level (window center) sets the middle of that range. A narrow window gives high contrast for similar tissues, such as the brain; a wide window shows everything from air to bone, as in the lung or bone presets.
Why does my CT look completely gray or black?
The default window from the file may not suit what you want to see, or the file has none. Pick a preset such as CT soft tissue (center 40, width 400) or Full range, or drag on the image to find the right contrast. CT values are converted to Hounsfield units with the Rescale Slope and Intercept tags, where water is 0 and air is about -1000.
Which DICOM compressions are supported?
Uncompressed files in implicit or explicit VR little endian, explicit VR big endian, deflated explicit VR, RLE lossless and 8-bit baseline JPEG are supported. JPEG 2000, JPEG-LS and lossless JPEG need specialized decoders that this browser tool does not include; their tags are still shown and a clear message explains why the image cannot be drawn.
Is it safe to open patient scans here?
The files never leave your device: they are read and displayed with JavaScript in your browser and are not sent to any server. Turn on Hide patient details before sharing a screenshot to mask the name, ID and birth date in the overlay and the tag table.
Can I use this viewer for diagnosis?
No. It is a general-purpose viewer for education, curiosity and quick checks, not a certified medical device. Screens, browsers and lossy exports can change how an image looks, so diagnostic reading must be done with approved software by qualified professionals.
How do I convert a DICOM image to PNG or JPG?
Open the file, set the window and level so the image looks the way you want, then press Download PNG. The current frame is saved at its original resolution with your contrast, rotation and flip settings applied. Convert the PNG to JPG with an image converter if you need a smaller file.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.