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Comparing the same files results in differences

https://imagemagick.com/discourse-server/viewtopic.php?t=20660

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Comparing the same files results in differences

Posted: 2012-04-02T12:26:49-07:00
by sven
Problem
When comparing an image with itself the result using the option -metric AE is expected to be 0. However, the result in case of the file below is (most frequently a value around) 487.

File
Download file

Commands

Code: Select all

convert -density 300 testfile.pdf testfile_1.tif
convert -density 300 testfile.pdf testfile_2.tif
compare -density 300 -metric AE testfile_1.tif testfile_2.tif testfile_out.pdf
Result
487 (= number of different pixels)
Please note that this value is not always the same using the same command on the same system.

Enlarged result
Note the red pixels.
Image

Note: TIFF files are different

Code: Select all

md5 testfile_1.tif testfile_2.tif 
MD5 (testfile_1.tif) = 5ee81c2214fc719eabaf004aa349c637
MD5 (testfile_2.tif) = c351ce04a9570d795c32ec839a0897c0
Version of ImageMagick
ImageMagick 6.7.6-0 2012-04-01 Q16

Version of GhostScript
GPL Ghostscript 9.05 (2012-02-08)

Results of calling convert -list format

Code: Select all

   Format  Module    Mode  Description
-------------------------------------------------------------------------------
      3FR  DNG       r--   Hasselblad CFV/H3D39II
        A* RAW       rw+   Raw alpha samples
      AAI* AAI       rw+   AAI Dune image
       AI  PDF       rw-   Adobe Illustrator CS2
      ART* ART       rw-   PFS: 1st Publisher Clip Art
      ARW  DNG       r--   Sony Alpha Raw Image Format
      AVI  MPEG      r--   Microsoft Audio/Visual Interleaved
      AVS* AVS       rw+   AVS X image
        B* RAW       rw+   Raw blue samples
      BGR* BGR       rw+   Raw blue, green, and red samples
     BGRA* BGR       rw+   Raw blue, green, red, and alpha samples
      BMP* BMP       rw-   Microsoft Windows bitmap image
     BMP2* BMP       -w-   Microsoft Windows bitmap image (V2)
     BMP3* BMP       -w-   Microsoft Windows bitmap image (V3)
      BRF* BRAILLE   -w-   BRF ASCII Braille format
        C* RAW       rw+   Raw cyan samples
      CAL* CALS      rw-   Continuous Acquisition and Life-cycle Support Type 1
           Specified in MIL-R-28002 and MIL-PRF-28002
     CALS* CALS      rw-   Continuous Acquisition and Life-cycle Support Type 1
           Specified in MIL-R-28002 and MIL-PRF-28002
   CANVAS* XC        r--   Constant image uniform color
  CAPTION* CAPTION   r--   Caption
      CIN* CIN       rw-   Cineon Image File
      CIP* CIP       -w-   Cisco IP phone image format
     CLIP* CLIP      -w+   Image Clip Mask
     CMYK* CMYK      rw+   Raw cyan, magenta, yellow, and black samples
    CMYKA* CMYK      rw+   Raw cyan, magenta, yellow, black, and alpha samples
      CR2  DNG       r--   Canon Digital Camera Raw Image Format
      CRW  DNG       r--   Canon Digital Camera Raw Image Format
      CUR* CUR       rw-   Microsoft icon
      CUT* CUT       r--   DR Halo
      DCM* DCM       r--   Digital Imaging and Communications in Medicine image
           DICOM is used by the medical community for images like X-rays.  The
           specification, "Digital Imaging and Communications in Medicine
           (DICOM)", is available at http://medical.nema.org/.  In particular,
           see part 5 which describes the image encoding (RLE, JPEG, JPEG-LS),
           and supplement 61 which adds JPEG-2000 encoding.
      DCR  DNG       r--   Kodak Digital Camera Raw Image File
      DCX* PCX       rw+   ZSoft IBM PC multi-page Paintbrush
      DDS* DDS       r--   Microsoft DirectDraw Surface
    DFONT* TTF       r--   Multi-face font package (Freetype 2.4.9)
      DNG  DNG       r--   Digital Negative
      DOT  DOT       ---   Graphviz
      DPX* DPX       rw-   SMPTE 268M-2003 (DPX 2.0)
           Digital Moving Picture Exchange Bitmap, Version 2.0.
           See SMPTE 268M-2003 specification at http://www.smtpe.org
           
     EPDF  PDF       rw-   Encapsulated Portable Document Format
      EPI  PS        rw-   Encapsulated PostScript Interchange format
      EPS  PS        rw-   Encapsulated PostScript
     EPS2* PS2       -w-   Level II Encapsulated PostScript
     EPS3* PS3       -w+   Level III Encapsulated PostScript
     EPSF  PS        rw-   Encapsulated PostScript
     EPSI  PS        rw-   Encapsulated PostScript Interchange format
      EPT  EPT       rw-   Encapsulated PostScript with TIFF preview
     EPT2  EPT       rw-   Encapsulated PostScript Level II with TIFF preview
     EPT3  EPT       rw+   Encapsulated PostScript Level III with TIFF preview
      ERF  DNG       r--   Epson RAW Format
      FAX* FAX       rw+   Group 3 FAX
           FAX machines use non-square pixels which are 1.5 times wider than
           they are tall but computer displays use square pixels, therefore
           FAX images may appear to be narrow unless they are explicitly
           resized using a geometry of "150x100%".
           
     FITS* FITS      rw-   Flexible Image Transport System
  FRACTAL* PLASMA    r--   Plasma fractal image
      FTS* FTS       rw-   Flexible Image Transport System
        G* RAW       rw+   Raw green samples
       G3* FAX       rw-   Group 3 FAX
      GIF* GIF       rw+   CompuServe graphics interchange format
    GIF87* GIF       rw-   CompuServe graphics interchange format (version 87a)
 GRADIENT* GRADIENT  r--   Gradual linear passing from one shade to another
     GRAY* GRAY      rw+   Raw gray samples
   GROUP4* TIFF      rw-   Raw CCITT Group4
     HALD*           r--   Identity Hald color lookup table image
      HDR* HDR       rw+   Radiance RGBE image format
HISTOGRAM* HISTOGRAM -w-   Histogram of the image
      HRZ* HRZ       rw-   Slow Scan TeleVision
      HTM* HTML      -w-   Hypertext Markup Language and a client-side image map
     HTML* HTML      -w-   Hypertext Markup Language and a client-side image map
      ICB* TGA       rw-   Truevision Targa image
      ICO* ICON      rw+   Microsoft icon
     ICON* ICON      rw-   Microsoft icon
     INFO  INFO      -w+   The image format and characteristics
   INLINE* INLINE    r--   Base64-encoded inline images
      IPL* IPL       rw+   IPL Image Sequence
   ISOBRL* BRAILLE   -w-   ISO/TR 11548-1 format
      JNG* PNG       rw-   JPEG Network Graphics
           See http://www.libpng.org/pub/mng/ for details about the JNG
           format.
     JPEG* JPEG      rw-   Joint Photographic Experts Group JFIF format (80)
      JPG* JPEG      rw-   Joint Photographic Experts Group JFIF format (80)
        K* RAW       rw+   Raw black samples
      K25  DNG       r--   Kodak Digital Camera Raw Image Format
      KDC  DNG       r--   Kodak Digital Camera Raw Image Format
    LABEL* LABEL     r--   Image label
        M* RAW       rw+   Raw magenta samples
      M2V  MPEG      rw+   MPEG Video Stream
      M4V  MPEG      rw+   Raw MPEG-4 Video
      MAC* MAC       r--   MAC Paint
      MAP* MAP       rw-   Colormap intensities and indices
      MAT  MAT       rw+   MATLAB level 5 image format
    MATTE* MATTE     -w+   MATTE format
      MEF  DNG       r--   Mamiya Raw Image File
     MIFF* MIFF      rw+   Magick Image File Format
      MNG* PNG       rw+   Multiple-image Network Graphics (libpng 1.4.10)
           See http://www.libpng.org/pub/mng/ for details about the MNG
           format.
     MONO* MONO      rw-   Raw bi-level bitmap
      MOV  MPEG      rw+   MPEG Video Stream
      MP4  MPEG      rw+   MPEG-4 Video Stream
      MPC* MPC       rw+   Magick Persistent Cache image format
     MPEG  MPEG      rw+   MPEG Video Stream
      MPG  MPEG      rw+   MPEG Video Stream
      MRW  DNG       r--   Sony (Minolta) Raw Image File
      MSL* MSL       rw+   Magick Scripting Language
     MSVG  SVG       rw+   ImageMagick's own SVG internal renderer
      MTV* MTV       rw+   MTV Raytracing image format
      MVG* MVG       rw-   Magick Vector Graphics
      NEF  DNG       r--   Nikon Digital SLR Camera Raw Image File
      NRW  DNG       r--   Nikon Digital SLR Camera Raw Image File
     NULL* NULL      rw-   Constant image of uniform color
        O* RAW       rw+   Raw opacity samples
      ORF  DNG       r--   Olympus Digital Camera Raw Image File
      OTB* OTB       rw-   On-the-air bitmap
      OTF* TTF       r--   Open Type font (Freetype 2.4.9)
      PAL* UYVY      rw-   16bit/pixel interleaved YUV
     PALM* PALM      rw+   Palm pixmap
      PAM* PNM       rw+   Common 2-dimensional bitmap format
  PATTERN* PATTERN   r--   Predefined pattern
      PBM* PNM       rw+   Portable bitmap format (black and white)
      PCD* PCD       rw-   Photo CD
     PCDS* PCD       rw-   Photo CD
      PCL  PCL       rw+   Printer Control Language
      PCT* PICT      rw-   Apple Macintosh QuickDraw/PICT
      PCX* PCX       rw-   ZSoft IBM PC Paintbrush
      PDB* PDB       rw+   Palm Database ImageViewer Format
      PDF  PDF       rw+   Portable Document Format
     PDFA  PDF       rw+   Portable Document Archive Format
      PEF  DNG       r--   Pentax Electronic File
      PES* PES       r--   Embrid Embroidery Format
      PFA* TTF       r--   Postscript Type 1 font (ASCII) (Freetype 2.4.9)
      PFB* TTF       r--   Postscript Type 1 font (binary) (Freetype 2.4.9)
      PFM* PFM       rw+   Portable float format
      PGM* PNM       rw+   Portable graymap format (gray scale)
    PICON* XPM       rw-   Personal Icon
     PICT* PICT      rw-   Apple Macintosh QuickDraw/PICT
      PIX* PIX       r--   Alias/Wavefront RLE image format
    PJPEG* JPEG      rw-   Joint Photographic Experts Group JFIF format (80)
   PLASMA* PLASMA    r--   Plasma fractal image
      PNG* PNG       rw-   Portable Network Graphics (libpng 1.4.10)
           See http://www.libpng.org/ for details about the PNG format.
    PNG24* PNG       rw-   opaque 24-bit RGB (zlib 1.2.6)
    PNG32* PNG       rw-   opaque or transparent 32-bit RGBA
     PNG8* PNG       rw-   8-bit indexed with optional binary transparency
      PNM* PNM       rw+   Portable anymap
      PPM* PNM       rw+   Portable pixmap format (color)
  PREVIEW* PREVIEW   -w-   Show a preview an image enhancement, effect, or f/x
       PS  PS        rw+   PostScript
      PS2* PS2       -w+   Level II PostScript
      PS3* PS3       -w+   Level III PostScript
      PSB* PSD       rw+   Adobe Large Document Format
      PSD* PSD       rw+   Adobe Photoshop bitmap
     PTIF* TIFF      rw+   Pyramid encoded TIFF
      PWP* PWP       r--   Seattle Film Works
        R* RAW       rw+   Raw red samples
RADIAL-GRADIENT* GRADIENT  r--   Gradual radial passing from one shade to another
      RAF  DNG       r--   Fuji CCD-RAW Graphic File
      RAS* SUN       rw+   SUN Rasterfile
      RGB* RGB       rw+   Raw red, green, and blue samples
     RGBA* RGB       rw+   Raw red, green, blue, and alpha samples
     RGBO* RGB       rw+   Raw red, green, blue, and opacity samples
      RLA* RLA       r--   Alias/Wavefront image
      RLE* RLE       r--   Utah Run length encoded image
      SCR* SCR       r--   ZX-Spectrum SCREEN$
      SCT* SCT       r--   Scitex HandShake
      SFW* SFW       r--   Seattle Film Works
      SGI* SGI       rw+   Irix RGB image
    SHTML* HTML      -w-   Hypertext Markup Language and a client-side image map
      SR2  DNG       r--   Sony Raw Format 2
      SRF  DNG       r--   Sony Raw Format
  STEGANO* STEGANO   r--   Steganographic image
      SUN* SUN       rw+   SUN Rasterfile
      SVG  SVG       rw+   Scalable Vector Graphics (XML 2.7.8)
     SVGZ  SVG       rw+   Compressed Scalable Vector Graphics (XML 2.7.8)
     TEXT* TXT       rw+   Text
      TGA* TGA       rw-   Truevision Targa image
THUMBNAIL* THUMBNAIL -w+   EXIF Profile Thumbnail
     TIFF* TIFF      rw+   Tagged Image File Format (LIBTIFF, Version 3.9.5)
   TIFF64* TIFF      ---   Tagged Image File Format (64-bit) (LIBTIFF, Version 3.9.5)
     TILE* TILE      r--   Tile image with a texture
      TIM* TIM       r--   PSX TIM
      TTC* TTF       r--   TrueType font collection (Freetype 2.4.9)
      TTF* TTF       r--   TrueType font (Freetype 2.4.9)
      TXT* TXT       rw+   Text
     UBRL* BRAILLE   -w-   Unicode Text format
      UIL* UIL       -w-   X-Motif UIL table
     UYVY* UYVY      rw-   16bit/pixel interleaved YUV
      VDA* TGA       rw-   Truevision Targa image
    VICAR* VICAR     rw-   VICAR rasterfile format
      VID* VID       rw+   Visual Image Directory
     VIFF* VIFF      rw+   Khoros Visualization image
      VST* TGA       rw-   Truevision Targa image
     WBMP* WBMP      rw-   Wireless Bitmap (level 0) image
     WEBP* WEBP      rw-   WebP Image Format
      WMV  MPEG      rw+   Windows Media Video
      WPG* WPG       r--   Word Perfect Graphics
        X* X         rw+   X Image
      X3F  DNG       r--   Sigma Camera RAW Picture File
      XBM* XBM       rw-   X Windows system bitmap (black and white)
       XC* XC        r--   Constant image uniform color
      XCF* XCF       r--   GIMP image
      XPM* XPM       rw-   X Windows system pixmap (color)
      XPS  XPS       r--   Microsoft XML Paper Specification
       XV* VIFF      rw+   Khoros Visualization image
      XWD* XWD       rw-   X Windows system window dump (color)
        Y* RAW       rw+   Raw yellow samples
    YCbCr* YCbCr     rw+   Raw Y, Cb, and Cr samples
   YCbCrA* YCbCr     rw+   Raw Y, Cb, Cr, and alpha samples
      YUV* YUV       rw-   CCIR 601 4:1:1 or 4:2:2

* native blob support
r read support
w write support
+ support for multiple images

Re: Comparing the same files results in differences

Posted: 2012-04-03T00:14:11-07:00
by anthony
The TIFF md5 being different is not suprising. It may have a different 'creation date'. JPEG and PNG images have the same thing.


Howver having different image data. That is suprizing. The only thing I can think of is that ghostscript is doing some randomized dithering. Perhaps without initializing the dither registers at the start. I have seen dither algorithms do that before.

Try runing the ghostscript equivelent directly and comparing its output.
See IM Examples, Using Ghostscript Directly
http://www.imagemagick.org/Usage/text/#ghostscript

Re: Comparing the same files results in differences

Posted: 2012-04-03T02:03:16-07:00
by sven
Anthony,

Thanks for your reply.

Obviously, there's no issue when running GhostScript directly.
Here's what I've tried:

Code: Select all

gs -dBATCH -dNOPAUSE -sDEVICE=tiff48nc -r300x300 -sOutputFile=gs_file1.tif logo.pdf
gs -dBATCH -dNOPAUSE -sDEVICE=tiff48nc -r300x300 -sOutputFile=gs_file2.tif logo.pdf
compare -density 300 -metric AE gs_file1.tif gs_file2.tif gs_out.pdf
Result
0

Here are the corresponding files:
Download files

Any ideas?

Cheers,
Sven

Re: Comparing the same files results in differences

Posted: 2012-04-05T06:55:47-07:00
by sven
So is this a bug in ImageMagick, since the results using GhostScript directly are correct?

Re: Comparing the same files results in differences

Posted: 2012-04-08T20:03:28-07:00
by anthony
I would use the PbmPLus encoded for gjostscript before discounting it.
That and PNG encoder is what IM uses.

Re: Comparing the same files results in differences

Posted: 2012-04-10T01:54:41-07:00
by sven
Anthony,

Thanks for your reply.
However, to be honest, I have no idea how to do so. Would you be so kind and assist me in this case?

Re: Comparing the same files results in differences

Posted: 2012-04-11T00:02:25-07:00
by anthony
Adding -verbose to convert before reading the image will print the delegate command (for "gs") so you can see what IM is doing.
the -f options are for the input file (saved to /tmp to allow the use of pipelined images and security measures).

Re: Comparing the same files results in differences

Posted: 2012-05-21T08:33:38-07:00
by sven
This is the Ghostscript command used by ImageMagick:

Code: Select all

"gs" -q -dQUIET -dSAFER -dBATCH -dNOPAUSE -dNOPROMPT -dMaxBitmap=500000000 -dAlignToPixels=0 -dGridFitTT=2 "-sDEVICE=pngalpha" -dTextAlphaBits=4 -dGraphicsAlphaBits=4 "-r150x150"  "-sOutputFile=/tmp/magick-IW9e6gXg-%08d" "-f/tmp/magick-eHVqVwOS" "-f/tmp/magick-Q1JxSVFu"
Using this command with Ghostscript directly leads to no differences. Using ImageMagick instead results in differences.
So this indicates a problem with ImageMagick...?
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