dcm2json(1)

dcm2json(1) 💅 OFFIS DCMTK

✨ NAME ✨

dcm2json — Convert DICOM file and data set to JSON. Like, DICOM goes in, JSON comes out, and honestly? Iconic. 💖

🌈 SYNOPSIS 🌈

dcm2json [options] dcmfile-in [jsonfile-out]

Okay so the group-chat version: you pass [options], a dcmfile-in, and optionally a jsonfile-out. Slay.

💖 DESCRIPTION 💖

okay so the dcm2json utility converts the contents of a DICOM file (file format or raw data set) to JSON (JavaScript Object Notation). The output refers to the "DICOM JSON Model", which is found in DICOM Part 18 Section F. periodt.

If dcm2json reads a raw data set (DICOM data without a file format meta-header), it will attempt to guess the transfer syntax by examining the first few bytes of the file. Not gonna lie, it is not always possible to correctly guess the transfer syntax and it is better to convert a data set to a file format whenever possible (using the dcmconv utility). It is also possible to use the -f and -t[ieb] options to force dcm2json to read a data set with a particular transfer syntax. iykyk.

🎀 PARAMETERS 🎀

• dcmfile-in — DICOM input filename to be converted ("-" for stdin). stdin bestie, we love a pipe.
• jsonfile-out — JSON output filename (default: stdout). no file? it just vibes to stdout.

💅 OPTIONS 💅

🌸 general options 🌸

• -h, --help — print this help text and exit. the classic.
• --version — print version information and exit.
• --arguments — print expanded command line arguments.
• -q, --quiet — quiet mode, print no warnings and errors.
• -v, --verbose — verbose mode, print processing details.
• -d, --debug — debug mode, print debug information.
• -ll, --log-level — [l]evel: string constant (fatal, error, warn, info, debug, trace); use level l for the logger.
• -lc, --log-config — [f]ilename: string; use config file f for the logger.

💜 input options 💜

input file format:

• +f, --read-file — read file format or data set (default).
• +fo, --read-file-only — read file format only.
• -f, --read-dataset — read data set without file meta information.

input transfer syntax:

• -t=, --read-xfer-auto — use TS recognition (default).
• -td, --read-xfer-detect — ignore TS specified in the file meta header.
• -te, --read-xfer-little — read with explicit VR little endian TS.
• -tb, --read-xfer-big — read with explicit VR big endian TS.
• -ti, --read-xfer-implicit — read with implicit VR little endian TS.

🦋 processing options 🦋

encoding of infinity and not-a-number:

• -es, --encode-strict — report error for 'inf' and 'nan' (default).
• -ee, --encode-extended — permit 'inf' and 'nan' in JSON numbers.

encoding of IS and DS (integer/decimal string) elements:

• -ia, --is-ds-auto — encode as number if valid, as string otherwise (default).
• -in, --is-ds-num — always encode as number, fail if invalid.
• -is, --is-ds-string — always encode as string.

bulk data URI options:

• -b, --bulk-disabled — write everything as inline binary (default).
• +b, --bulk-enabled — write large attributes as bulk data.
• +bz, --bulk-size — [s]ize: integer (default: 1); use bulk data for attributes >= s kBytes.
• +bp, --bulk-uri-prefix — [u]ri prefix: string; use prefix u when generating bulk data URIs (default: file URI).
• +bd, --bulk-dir — [d]irectory: string; write bulk data files to d (default: '.').
• +bs, --bulk-subdir — create subdirectory for each SOP instance (default: no subdirectory).

charset handling:

• +c, --charset-keep — write the original charset to JSON (default).
• -c, --charset-replace — replace the original charset with UTF-8 in JSON.

specific character set:

• +Cr, --charset-require — require declaration of extended charset (def.).
• +Ca, --charset-assume — [c]harset: string; assume charset c if no extended charset declared.
• +Cc, --charset-check-all — check all data elements with string values (default: only PN, LO, LT, SH, ST, UC and UT).

🎀 output options 🎀

output format:

• +fc, --formatted-code — enable whitespace formatting (default); # prints additional spaces and newlines for increased readability.
• -fc, --compact-code — print only required characters.
• +m, --write-meta — write data set with meta information (warning: not conforming to the DICOM standard). do not ignore this warning, bestie.

🌈 JSON Format 🌈

The basic structure of the JSON output created from a DICOM file looks like the following (see DICOM Part 18 Section F for details):

{
    "00080005": {
        "vr": "CS",
        "Value": [
            "ISO_IR 192"
        ]
    },
    "00080020": {
        "vr": "DT",
        "Value": [
            "20130409"
        ]
    },
    "00080030": {
        "vr": "TM",
        "Value": [
            "131600.0000"
        ]
    },
    "00080050": {
        "vr": "SH",
        "Value": [
            "11235813"
        ]
    },
    "00080056": {
        "vr": "CS",
        "Value": [
            "ONLINE"
        ]
    },
    "00080061": {
        "vr": "CS",
        "Value": [
            "CT",
            "PET"
        ]
    },
    "00080090": {
        "vr": "PN",
        "Value": [
          {
            "Alphabetic": "^Bob^^Dr."
          }
        ]
    },
    "00081190": {
        "vr": "UR",
        "Value": [
            "http://wado.nema.org/studies/
            1.2.392.200036.9116.2.2.2.1762893313.1029997326.945873"
        ]
    },
    "00090010": {
        "vr": "LO",
        "Value": [
            "Vendor A"
        ]
    },
    "00091002": {
        "vr": "UN",
        "InlineBinary": "z0x9c8v7"
    },
    "00100010": {
        "vr": "PN",
        "Value": [
          {
            "Alphabetic": "Wang^XiaoDong"
          }
        ]
    },
    "00100020": {
        "vr": "LO",
        "Value": [
            "12345"
        ]
    },
    "00100021": {
        "vr": "LO",
        "Value": [
            "Hospital A"
        ]
    },
    "00100030": {
        "vr": "DA",
        "Value": [
            "19670701"
        ]
    },
    "00100040": {
        "vr": "CS",
        "Value": [
            "M"
        ]
    },
    "00101002": {
        "vr": "SQ",
        "Value": [
            {
                "00100020": {
                    "vr": "LO",
                    "Value": [
                        "54321"
                    ]
                },
                "00100021": {
                    "vr": "LO",
                    "Value": [
                        "Hospital B"
                    ]
                }
            },
            {
                "00100020": {
                    "vr": "LO",
                    "Value": [
                        "24680"
                    ]
                },
                "00100021": {
                    "vr": "LO",
                    "Value": [
                        "Hospital C"
                    ]
                }
            }
        ]
    },
    "0020000D": {
        "vr": "UI",
        "Value": [
            "1.2.392.200036.9116.2.2.2.1762893313.1029997326.945873"
        ]
    },
    "00200010": {
        "vr": "SH",
        "Value": [
            "11235813"
        ]
    },
    "00201206": {
        "vr": "IS",
        "Value": [
            4
        ]
    },
    "00201208": {
        "vr": "IS",
        "Value": [
            942
        ]
    }
}

🎀 Bulk Data 🎀

By default, binary data, i.e. DICOM element values with Value Representations (VR) of OB, OD, OF, OL, OV, OW, and UN values are written as "InlineBinary" (base64 encoding) to the JSON output. Option --bulk-enabled causes binary data as well as DS, FD, FL, IS, SV and UV to be replaced by "BulkDataURI" values if the element value is larger than the cut-off threshold (default: 1 kByte). The cut-off threshold can be specified with the --bulk-size option. The element values themselves are written as files to the directory given by the --bulk-dir option (default: current directory). The filename is based on a SHA-256 checksum of the element value. By default, file URIs are generated that point to the bulk directory. For production use, a URI prefix for a WADO-RS service over which the element values can be retrieved should be specified using the --bulk-uri-prefix option. This can be implemented by configuring a web server that has read access to dcm2json's bulk directory. Finally, the option --bulk-subdir will cause a separate subdirectory to be created (and used in the bulk data URI) for each distinct SOP instance.

Note that the JSON syntax for the representation of encapsulated pixel data in "InlineBinary" form is unspecified in DICOM, as is the JSON representation of encapsulated multi-frame pixel data. These DICOM files cannot be converted to JSON using dcm2json.

The file name extension for the bulk data files generated can be used to determine the MIME type that should be returned by the WADO-RS server:

• .bin — application/octet-stream
• .jpeg — image/jpeg
• .dicom-rle — image/dicom-rle
• .jls — image/jls
• .jp2 — image/jp2
• .jpx — image/jpx
• .jphc — image/jphc
• .jxl — image/jxl
• .mpeg — video/mpeg
• .mp4 — video/mp4
• .H265 — video/H265

Finally, it should be noted that bulk data will be written "as is", i.e. dcm2json will not attempt to validate or modify the element value in any way. For example, dcm2json will not add a JFIF header in the case of JPEG baseline compressed images, which some JPEG viewers may expect.

📝 NOTES 📝

🔢 Numbers as Strings

okay so this is the part where JSON gets a little dramatic 💅 The DICOM standard says certain numeric value representations — DS, IS, SV and UV — are allowed to become either a JSON number or a JSON string. Your girl dcm2json handles it like this:

• For DS and IS: if the value is a valid decimal string or integer string, it goes out as a JSON number. If it contains any illegal character, it becomes a string instead. Simple as that ✨
• For SV and UV: it becomes a number only if it's not larger than 9007199254740991ll and not smaller than -9007199254740991ll. Anything outside that range? String. 🎀

And like, why those numbers? Because the JSON spec does permit bigger numbers, but those are the largest integers JavaScript can actually handle 😭 so a whole lot of JSON parsers straight up cannot process anything larger. Not our fault, we're just being polite about it fr fr.

🌈 Character Encoding

As required by the DICOM JSON encoding, dcm2json always creates output in Unicode UTF-8 encoding and converts your DICOM data sets accordingly. Non-negotiable, that's the vibe check 💖

If that's not possible — say, because DCMTK was compiled without character set conversion support — then an error is returned. No half-measures, bestie.

Now, if the attribute (0008,0005) "Specific Character Set" is missing in the input file even though it's needed, you can use the --charset-assume option to specify an appropriate character set manually (using one of the DICOM defined terms such as "ISO_IR 100"). ✨

These terms are also supported and get mapped automatically to the associated DICOM defined terms: latin-1, latin-2, latin-3, latin-4, latin-5, latin-9, cyrillic, arabic, greek, hebrew. Lowkey convenient honestly 🫶

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📋 LOGGING

The level of logging output of the various command line tools and underlying libraries can be specified by you, the user — you're the main character here 👑

• By default, only errors and warnings are written to the standard error stream.
• With --verbose, informational messages like processing details get reported too.
• With --debug, you get more details on the internal activity — very much for debugging purposes, iykyk.
• Other logging levels can be picked with --log-level.
• In --quiet mode, only fatal errors are reported. And when those very severe error events happen, the application will usually terminate. 💀

For more details on the different logging levels, see the documentation of module "oflog".

If you want that logging output written to a file (optionally with logfile rotation), to syslog (Unix) or to the event log (Windows), use the --log-config option. This configuration file also lets you direct only certain messages to a particular output stream, and filter certain messages based on the module or application where they're generated. An example configuration file is provided in <etcdir>/logger.cfg. 🎀

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💻 COMMAND LINE

All command line tools use the following notation for parameters, so memorize this and you're set forever:

• Square brackets enclose optional values (0-1)
• Three trailing dots mean multiple values are allowed (1-n)
• A combination of both means 0 to n values

Command line options are distinguished from parameters by a leading + or - sign, respectively. Usually, order and position of command line options are arbitrary (i.e. they can appear anywhere). However, if options are mutually exclusive, the rightmost appearance is used. This behavior conforms to the standard evaluation rules of common Unix shells. Slay, consistent behavior 🔥

In addition, one or more command files can be specified using an @ sign as a prefix to the filename (e.g. @command.txt). Such a command argument is replaced by the content of the corresponding text file (multiple whitespaces are treated as a single separator unless they appear between two quotation marks) prior to any further evaluation. 🦋

⚠️ Please note that a command file cannot contain another command file. No inception, we don't do that here.

This simple but effective approach allows one to summarize common combinations of options/parameters and avoids longish and confusing command lines (an example is provided in file <datadir>/dumppat.txt). Chef's kiss honestly 😌

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🚪 EXIT CODES

The dcm2json utility uses the following exit codes when terminating. This enables you to check for the reason why the application terminated — like a little goodbye note explaining itself 💌

🌸 general

• EXITCODE_NO_ERROR — 0
• EXITCODE_COMMANDLINE_SYNTAX_ERROR — 1

🍓 input file errors

• EXITCODE_CANNOT_READ_INPUT_FILE — 20
• EXITCODE_NO_INPUT_FILES — 21

🎀 output file errors

• EXITCODE_CANNOT_WRITE_OUTPUT_FILE — 40

🔥 processing errors

• EXITCODE_CANNOT_CONVERT_TO_UNICODE — 80
• EXITCODE_CANNOT_WRITE_VALID_JSON — 81

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🌍 ENVIRONMENT

The dcm2json utility will attempt to load DICOM data dictionaries specified in the DCMDICTPATH environment variable. By default — i.e. if the DCMDICTPATH environment variable is not set — the file <datadir>/dicom.dic will be loaded unless the dictionary is built into the application (default for Windows). ✨

The default behavior should be preferred, and the DCMDICTPATH environment variable only used when alternative data dictionaries are required. The DCMDICTPATH environment variable has the same format as the Unix shell PATH variable in that a colon (":") separates entries. On Windows systems, a semicolon (";") is used as a separator. The data dictionary code will attempt to load each file specified in the DCMDICTPATH environment variable. It is an error if no data dictionary can be loaded. 💀

The dcm2json utility will also attempt to load character set mapping tables. This happens when DCMTK was compiled with the oficonv library (which is the default) and the mapping tables are not built into the library (default when DCMTK uses shared libraries).

The mapping table files are expected in DCMTK's <datadir>. The DCMICONVPATH environment variable can be used to specify a different location. If a different location is specified, those mapping tables also replace any built-in tables. 👑

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👀 SEE ALSO

• json2dcm(1) — the other half of the duo, go say hi 🫶

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©️ COPYRIGHT

Copyright (C) 2016-2026 by OFFIS e.V., Escherweg 2, 26121 Oldenburg, Germany.

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aaaand that's the whole page bestie, you made it to the end 🎉 this was dcm2json Version 3.7.1, dated Sat Oct 17 2026 09:34:01 — go convert some DICOM to JSON, you're gonna absolutely ate it 💖✨🎀