Provided by: dcmtk_3.6.4-2_amd64 bug

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

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 by OFFIS e.V., Escherweg 2, 26121 Oldenburg, Germany.