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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:

       o 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.

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

       o 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.

       o 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.

       o 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.

Version	3.6.6			Thu Jan	14 2021			    dcmicmp(1)

NAME | SYNOPSIS | DESCRIPTION | PARAMETERS | OPTIONS | NOTES | TRANSFER SYNTAXES | LOGGING | COMMAND LINE | EXIT CODES | ENVIRONMENT | SEE ALSO | COPYRIGHT

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