dcmicmp(1)                        OFFIS DCMTK                       dcmicmp(1)

NAME
       dcmicmp - Compare DICOM images and compute difference metrics


SYNOPSIS
       dcmicmp [options] dcmfile-in-1 dcmfile-in-2

DESCRIPTION
       The  dcmicmp  utility  reads  two  DICOM images, an original 'reference
       image' and a  post-processed  'test  image',  to  which  some  kind  of
       processing   such   as   a   lossy   image   compression,  followed  by
       decompression, has been applied. This tool requires  that  both  images
       have the same resolution, the same number of frames and are either both
       color or monochrome. Compressed images are not supported.

       The  dcmicmp  utility then compares both images and computes and prints
       metrics that describe how similar or different both images are:

       • the maximum absolute error is the largest difference between an pixel
         value in the reference image and the corresponding pixel value in the
         test image.

       • the mean absolute error  (MAE)  is  the  average  difference  between
         original pixel value and test image pixel value

       • the  root  mean square error (RMSE) is computed by adding the squares
         of all difference values, then  dividing  by  the  number  of  values
         added, and then taking the square root.

       • The  peak  signal to noise ratio (PSNR) considers the reference image
         as a signal and the differences between reference and test  image  as
         noise.  PSNR is the maximum signal strength (i.e. maximum pixel value
         in  the  reference  image)  divided  by  the  RMSE,  expressed  on  a
         logarithmic scale in dB.

       • The  signal  to noise ratio (PSNR) also considers the reference image
         as a signal and the differences between reference and test  image  as
         noise.  SNR  is  the  average  signal  strength  divided by the RMSE,
         expressed on a logarithmic scale in dB.

       All metrics are computed as defined in R.C. Gonzalez  and  R.E.  Woods,
       'Digital Image Processing,' Prentice Hall 2008.

PARAMETERS
       dcmfile-in-1  Reference DICOM image file for comparison

       dcmfile-in-2  Test DICOM image file for comparison ("-" for stdin)

OPTIONS
   general options
         -h    --help
                 print this help text and exit

               --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

   image processing options
       modality LUT transformation:

         +M    --use-modality
                 use modality LUT transformation (default)

         -M    --no-modality
                 ignore stored modality LUT transformation

       VOI LUT transformation:

         -W    --no-windowing
                 no VOI windowing (default)

         +Wi   --use-window  [n]umber: integer
                 use the n-th VOI window from image file

         +Wl   --use-voi-lut  [n]umber: integer
                 use the n-th VOI look up table from image file

         +Wm   --min-max-window
                 compute VOI window using min-max algorithm
                 on both images separately

         +Wn   --min-max-window-n
                 compute VOI window using min-max algorithm
                 on both images separately, ignoring extremes

         +Wr   --min-max-ref
                 compute VOI window using min-max algorithm
                 and use same window for the test image

         +Wq   --min-max-n-ref
                 compute VOI window using min-max algorithm,
                 ignoring extreme values
                 and use same window for the test image

         +Ww   --set-window  [c]enter [w]idth: float
                 compute VOI window using center c and width w

         +Wfl  --linear-function
                 set VOI LUT function to LINEAR

         +Wfs  --sigmoid-function
                 set VOI LUT function to SIGMOID

       presentation LUT transformation:

         +Pid  --identity-shape
                 set presentation LUT shape to IDENTITY

         +Piv  --inverse-shape
                 set presentation LUT shape to INVERSE

         +Pod  --lin-od-shape
                 set presentation LUT shape to LIN OD

   image comparison metrics options
         +ce   --check-error  [l]imit: integer
                 check if max absolute error <= limit

         # Return exit code EXITCODE_LIMIT_EXCEEDED_MAX_ERROR if the computed
         # maximum absolute error is larger than the given limit.

         +cm   --check-mae  [l]imit: float
                 check if mean absolute error <= limit

         # Return exit code EXITCODE_LIMIT_EXCEEDED_MAE if the computed
         # mean absolute error is larger than the given limit.

         +cr   --check-rmse  [l]imit: float
                 check if root mean square error <= limit

         # Return exit code EXITCODE_LIMIT_EXCEEDED_RMSE if the computed
         # root mean square error is larger than the given limit.

         +cp   --check-psnr  [l]imit: float
                 check if PSNR >= limit

         # Return exit code EXITCODE_LIMIT_EXCEEDED_PSNR if the computed
         # peak signal to noise ratio is smaller than the given limit
         # (for PSNR, higher values mean better image quality)

         +cs   --check-snr  [l]imit: float
                 check if SNR >= limit

         # Return exit code EXITCODE_LIMIT_EXCEEDED_PSNR if the computed
         # signal to noise ratio is smaller than the given limit
         # (for SNR, higher values mean better image quality)

   output options
         +sd   --save-diff  [f]ilename: string
                 write secondary capture difference image

         # Create a Multiframe Secondary Capture image that contains a
         # difference image between reference and test image. For monochrome
         # images, one difference frame is created for each frame in the reference
         # image. For color images, three monochrome frames are created for each
         # frame in the reference image, corresponding to the differences in the
         # red, green and blue color plane. The difference image will have
         # BitsStored 8 or 16, depending on the properties of the reference image.

         +a    --amplify  [f]actor: float
                 multiply diff image pixel values by f

         # This option can be used to amplify the grayscale values in the
         # difference image by multiplying each value with the given factor.
         # Alternatively, a DICOM VOI LUT window may be used when visualizing
         # the difference image.

NOTES
   grayscale display pipeline
       Monochrome  DICOM images require that a multi-stage display pipeline is
       executed in order to convert the raw  pixel  values  to  the  so-called
       presentation   values   (p-values)  that  are  sent  to  the  (possibly
       calibrated) display. When comparing the similarity of images before and
       after post-processing, it can be relevant to activate  some  stages  of
       this  display  pipeline  before  calculating  the  difference image and
       metrics. The image  processing  options  allow  the  caller  to  either
       activate  or  deactivate the Modality LUT, VOI LUT and Presentation LUT
       transformations. In any case, the same  transformation  is  applied  to
       both images, although possibly with different parameters if for example
       the  'first  VOI  LUT  window'  stored  in  each image is applied. This
       assumes that the post-processing algorithm (e.g. compression algorithm)
       has adapted the values of such windows during compression such that the
       image display after applying the window is as close as possible to  the
       reference.  For images with more than 8 bits/sample it may be important
       to known which VOI LUT transformation will be applied by the user  when
       viewing the image, because this may affect the perceived image quality.
       Therefore, absolute Window parameters can also be given with the --set-
       window option, which will then be applied to both images.

   suitability of images for diagnostic purposes
       The user should also note that the metrics computed by this tool cannot
       predict  or  estimate  the  suitability  of  lossy compressed image for
       diagnostic  purposes.  Much  more  complex  image  processing  and   an
       understanding of the image content (e.g. body part) would be needed for
       this  purpose.  The metrics computed provide an estimation of the level
       of distortion caused by the post-processing - no more and no less.

TRANSFER SYNTAXES
       dcmicmp supports the following transfer syntaxes for input:

       LittleEndianImplicitTransferSyntax             1.2.840.10008.1.2
       LittleEndianExplicitTransferSyntax             1.2.840.10008.1.2.1
       DeflatedExplicitVRLittleEndianTransferSyntax   1.2.840.10008.1.2.1.99 (*)
       BigEndianExplicitTransferSyntax                1.2.840.10008.1.2.2

       The difference image file is always written in Little  Endian  Implicit
       Transfer Syntax.

       (*) if compiled with zlib support enabled

LOGGING
       The  level  of  logging  output  of  the various command line tools and
       underlying libraries can be specified by the  user.  By  default,  only
       errors  and  warnings  are  written to the standard error stream. Using
       option --verbose also informational messages  like  processing  details
       are  reported.  Option  --debug  can be used to get more details on the
       internal activity, e.g. for debugging purposes.  Other  logging  levels
       can  be  selected  using option --log-level. In --quiet mode only fatal
       errors are reported. In such very severe error events, the  application
       will  usually  terminate.  For  more  details  on the different logging
       levels, see documentation of module 'oflog'.

       In case the logging output should be written to file  (optionally  with
       logfile  rotation),  to syslog (Unix) or the event log (Windows) option
       --log-config can be used.  This  configuration  file  also  allows  for
       directing  only  certain messages to a particular output stream and for
       filtering certain messages based on the  module  or  application  where
       they  are  generated.  An  example  configuration  file  is provided in
       <etcdir>/logger.cfg.

COMMAND LINE
       All command line tools  use  the  following  notation  for  parameters:
       square  brackets  enclose  optional  values  (0-1), three trailing dots
       indicate that 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.

       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.

EXIT CODES
       The dcmicmp utility uses the following  exit  codes  when  terminating.
       This  enables  the  user  to  check  for the reason why the application
       terminated.

   general
       EXITCODE_NO_ERROR                         0
       EXITCODE_COMMANDLINE_SYNTAX_ERROR         1

   input/output file errors
       EXITCODE_INVALID_INPUT_FILE              22
       EXITCODE_CANNOT_WRITE_OUTPUT_FILE        40

   image processing errors
       EXITCODE_INITIALIZE_DIFF_IMAGE           80
       EXITCODE_DISPLAY_PIPELINE                81
       EXITCODE_IMAGE_COMPARISON                82

   error codes for exceeded limits
       EXITCODE_LIMIT_EXCEEDED_MAX_ERROR        90
       EXITCODE_LIMIT_EXCEEDED_MAE              91
       EXITCODE_LIMIT_EXCEEDED_RMSE             92
       EXITCODE_LIMIT_EXCEEDED_PSNR             93
       EXITCODE_LIMIT_EXCEEDED_SNR              94

ENVIRONMENT
       The dcmicmp 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.

SEE ALSO
       dcm2pnm(1)

COPYRIGHT
       Copyright  (C)  2018-2024  by OFFIS e.V., Escherweg 2, 26121 Oldenburg,
       Germany.

Version 3.6.9                   Wed Dec 11 2024                     dcmicmp(1)
