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Conversion from PDF to PNG contains unwanted artifacts

Posted: 2015-02-04T12:12:44-07:00
by vmrob
While attempting to convert a pdf document to a png using the following command, the output is inconsistent with the input. Note the artifacts near the arrows.

Version:
$ convert --version
Version: ImageMagick 6.9.0-3 Q16 x86_64 2015-02-04 http://www.imagemagick.org
Copyright: Copyright (C) 1999-2015 ImageMagick Studio LLC
Features: DPC Modules
Delegates (built-in): bzlib cairo fontconfig freetype jng jp2 jpeg lcms ltdl lzma openexr png rsvg tiff webp xml zlib
Command:

Code: Select all

convert -density 400 gitdags.pdf gitdags.png
Input:
https://s3.amazonaws.com/vmrob/imagemag ... itdags.pdf

Output:
Image

Input PDF details:

Code: Select all

$ identify -verbose gitdags.pdf
Image: gitdags.pdf
  Format: PDF (Portable Document Format)
  Mime type: application/pdf
  Class: DirectClass
  Geometry: 159x76+0+0
  Resolution: 72x72
  Print size: 2.20833x1.05556
  Units: Undefined
  Type: PaletteAlpha
  Endianess: Undefined
  Colorspace: sRGB
  Depth: 16/8-bit
  Channel depth:
    red: 8-bit
    green: 8-bit
    blue: 8-bit
    alpha: 8-bit
  Channel statistics:
    Pixels: 12084
    Red:
      min: 0 (0)
      max: 65535 (1)
      mean: 18001.7 (0.274688)
      standard deviation: 24388.9 (0.37215)
      kurtosis: -0.914249
      skewness: 0.869938
      entropy: 0.385675
    Green:
      min: 0 (0)
      max: 65535 (1)
      mean: 18532.3 (0.282786)
      standard deviation: 24553.6 (0.374664)
      kurtosis: -1.06098
      skewness: 0.789896
      entropy: 0.395248
    Blue:
      min: 0 (0)
      max: 65535 (1)
      mean: 17772.3 (0.271187)
      standard deviation: 23235.7 (0.354554)
      kurtosis: -1.11204
      skewness: 0.743544
      entropy: 0.39425
    Alpha:
      min: 0 (0)
      max: 65535 (1)
      mean: 20267.9 (0.309268)
      standard deviation: 28534.5 (0.435408)
      kurtosis: -1.1953
      skewness: -0.833664
      entropy: 0.312278
  Image statistics:
    Overall:
      min: 0 (0)
      max: 65535 (1)
      mean: 24893.4 (0.379848)
      standard deviation: 25257.7 (0.385408)
      kurtosis: -0.919662
      skewness: 0.561842
      entropy: 0.371863
  Alpha: srgba(255,255,255,0)   #FFFFFFFFFFFF0000
  Colors: 195
  Histogram:
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        10: (14649,15934,16962,65535) #39393E3E4242 srgba(57,62,66,1)
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         1: (23130,28527,30326,35980) #5A5A6F6F76768C8C srgba(90,111,118,0.54902)
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         9: (23644,24158,21074,65535) #5C5C5E5E5252 srgba(92,94,82,1)
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         6: (23901,29041,30840,43176) #5D5D71717878A8A8 srgba(93,113,120,0.658824)
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         2: (24158,29298,30840,39064) #5E5E727278789898 srgba(94,114,120,0.596078)
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         1: (24415,29298,30840,34695) #5F5F727278788787 srgba(95,114,120,0.529412)
         1: (24672,29555,30840,51657) #606073737878C9C9 srgba(96,115,120,0.788235)
         4: (24672,29555,31097,35723) #6060737379798B8B srgba(96,115,121,0.545098)
         1: (24672,29555,31097,65535) #606073737979 srgba(96,115,121,1)
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         5: (25186,22102,23644,65535) #626256565C5C srgba(98,86,92,1)
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         3: (33924,29298,29298,65535) #848472727272 srgba(132,114,114,1)
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         3: (34952,34181,26471,65535) #888885856767 srgba(136,133,103,1)
         6: (35723,36237,31354,65535) #8B8B8D8D7A7A srgba(139,141,122,1)
         8: (36237,39835,42148,65535) #8D8D9B9BA4A4 srgba(141,155,164,1)
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        20: (37522,37522,37522, 8738) #9292929292922222 srgba(146,146,146,0.133333)
        19: (37522,37522,37522,13107) #9292929292923333 srgba(146,146,146,0.2)
        19: (37522,37522,37522,52428) #929292929292CCCC srgba(146,146,146,0.8)
        19: (37522,37522,37522,17476) #9292929292924444 srgba(146,146,146,0.266667)
        12: (37522,37522,37522,21845) #9292929292925555 srgba(146,146,146,0.333333)
        12: (37522,37522,37522,26214) #9292929292926666 srgba(146,146,146,0.4)
        11: (37522,37522,37522,  771) #9292929292920303 srgba(146,146,146,0.0117647)
        11: (37522,37522,37522,30583) #9292929292927777 srgba(146,146,146,0.466667)
        10: (37522,37522,37522,48059) #929292929292BBBB srgba(146,146,146,0.733333)
        10: (37522,37522,37522,56797) #929292929292DDDD srgba(146,146,146,0.866667)
         9: (37522,37522,37522, 5140) #9292929292921414 srgba(146,146,146,0.0784314)
         8: (37522,37522,37522,43690) #929292929292AAAA srgba(146,146,146,0.666667)
         8: (37522,37522,37522,61166) #929292929292EEEE srgba(146,146,146,0.933333)
         8: (37522,37522,37522, 2570) #9292929292920A0A srgba(146,146,146,0.0392157)
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         7: (37522,37522,37522,39321) #9292929292929999 srgba(146,146,146,0.6)
         5: (37522,37522,37522,65535) #929292929292 srgba(146,146,146,1)
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         4: (37522,37522,37522,43176) #929292929292A8A8 srgba(146,146,146,0.658824)
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         3: (37522,37522,37522, 1285) #9292929292920505 srgba(146,146,146,0.0196078)
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         2: (37522,37522,37522, 8481) #9292929292922121 srgba(146,146,146,0.129412)
         1: (37522,37522,37522, 7453) #9292929292921D1D srgba(146,146,146,0.113725)
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         1: (37522,37522,37522,23901) #9292929292925D5D srgba(146,146,146,0.364706)
         1: (37522,37522,37522,52685) #929292929292CDCD srgba(146,146,146,0.803922)
         1: (37522,37522,37522,54998) #929292929292D6D6 srgba(146,146,146,0.839216)
         1: (37522,37522,37522,16448) #9292929292924040 srgba(146,146,146,0.25098)
         1: (37522,37522,37522,13364) #9292929292923434 srgba(146,146,146,0.203922)
         1: (37522,37522,37522, 7710) #9292929292921E1E srgba(146,146,146,0.117647)
         1: (37522,37522,37522,57568) #929292929292E0E0 srgba(146,146,146,0.878431)
         1: (37522,37522,37522,35723) #9292929292928B8B srgba(146,146,146,0.545098)
         1: (37522,37522,37522,39578) #9292929292929A9A srgba(146,146,146,0.603922)
         1: (37522,37522,37522,41120) #929292929292A0A0 srgba(146,146,146,0.627451)
         1: (37522,37522,37522,46774) #929292929292B6B6 srgba(146,146,146,0.713725)
         1: (37522,37522,37522,48316) #929292929292BCBC srgba(146,146,146,0.737255)
         3: (38036,33153,35466,65535) #949481818A8A srgba(148,129,138,1)
         4: (38293,32896,32896,65535) #959580808080 srgba(149,128,128,1)
         1: (39321,38550,29812,65535) #999996967474 srgba(153,150,116,1)
         3: (39578,40349,34952,65535) #9A9A9D9D8888 srgba(154,157,136,1)
        22: (39835,43690,46260,65535) #9B9BAAAAB4B4 srgba(155,170,180,1)
         3: (42148,36751,39321,65535) #A4A48F8F9999 srgba(164,143,153,1)
         1: (42405,36751,36494,65535) #A5A58F8F8E8E srgba(165,143,142,1)
        26: (43433,44204,38550,65535) #A9A9ACAC9696 srgba(169,172,150,1)
         5: (43690,42919,33153,65535) #AAAAA7A78181 srgba(170,167,129,1)
         7: (43690,47802,50629,65535) #AAAABABAC5C5 srgba(170,186,197,1)
         1: (44204,38036,38036,65535) #ACAC94949494 srgba(172,148,148,1)
         8: (46260,40606,43433,65535) #B4B49E9EA9A9 srgba(180,158,169,1)
         9: (46774,40349,40092,65535) #B6B69D9D9C9C srgba(182,157,156,1)
        11: (47288,51657,54741,65535) #B8B8C9C9D5D5 srgba(184,201,213,1)
         5: (47545,48316,41891,65535) #B9B9BCBCA3A3 srgba(185,188,163,1)
         3: (48059,47031,36494,65535) #BBBBB7B78E8E srgba(187,183,142,1)
         3: (50629,44204,47288,65535) #C5C5ACACB8B8 srgba(197,172,184,1)
         5: (50886,43947,43690,65535) #C6C6ABABAAAA srgba(198,171,170,1)
        10: (50886,55769,59110,65535) #C6C6D9D9E6E6 srgba(198,217,230,1)
         9: (51400,52428,45489,65535) #C8C8CCCCB1B1 srgba(200,204,177,1)
         4: (52428,51400,39835,65535) #CCCCC8C89B9B srgba(204,200,155,1)
       547: (54484,59624,63222,65535) #D4D4E8E8F6F6 srgba(212,232,246,1)
         5: (54741,47802,51143,65535) #D5D5BABAC7C7 srgba(213,186,199,1)
         7: (55255,47545,47545,65535) #D7D7B9B9B9B9 srgba(215,185,185,1)
         7: (55512,56283,48830,65535) #D8D8DBDBBEBE srgba(216,219,190,1)
         2: (56797,55769,43176,65535) #DDDDD9D9A8A8 srgba(221,217,168,1)
         2: (59110,51657,55255,65535) #E6E6C9C9D7D7 srgba(230,201,215,1)
         2: (59367,51400,51143,65535) #E7E7C8C8C7C7 srgba(231,200,199,1)
      1117: (59367,60395,52428,65535) #E7E7EBEBCCCC srgba(231,235,204,1)
         2: (61166,59881,46517,65535) #EEEEE9E9B5B5 srgba(238,233,181,1)
       223: (63222,55255,59110,65535) #F6F6D7D7E6E6 srgba(246,215,230,1)
       176: (63736,54998,54741,65535) #F8F8D6D6D5D5 srgba(248,214,213,1)
       305: (65535,64250,49858,65535) #FFFFFAFAC2C2 srgba(255,250,194,1)
        76: (65535,65535,65535,    0) #FFFFFFFFFFFF0000 srgba(255,255,255,0)
  Rendering intent: Perceptual
  Gamma: 0.454545
  Chromaticity:
    red primary: (0.64,0.33)
    green primary: (0.3,0.6)
    blue primary: (0.15,0.06)
    white point: (0.3127,0.329)
  Background color: white
  Border color: srgba(223,223,223,1)
  Matte color: grey74
  Transparent color: none
  Interlace: None
  Intensity: Undefined
  Compose: Over
  Page geometry: 159x76+0+0
  Dispose: Undefined
  Iterations: 0
  Compression: Undefined
  Orientation: Undefined
  Properties:
    date:create: 2015-02-04T13:16:00-06:00
    date:modify: 2015-02-04T13:16:00-06:00
    pdf:Version: PDF-1.5 
    signature: 7e9bb187fbfef57c0e1a9c6c0862ad82b1efde9a64d842e3a627d4dc6457092a
  Artifacts:
    filename: gitdags.pdf
    verbose: true
  Tainted: False
  Filesize: 5.08KB
  Number pixels: 12.1K
  Pixels per second: 12.084EB
  User time: 0.000u
  Elapsed time: 0:01.000
  Version: ImageMagick 6.9.0-3 Q16 x86_64 2015-02-04 http://www.imagemagick.org

Re: Conversion from PDF to PNG contains unwanted artifacts

Posted: 2015-02-04T14:20:45-07:00
by pipitas
What 'identify -verbose some.pdf' tells you are many details supposedly about the input PDF which are not relevant at all for the PDF. The reason: identify (as ImageMagick in general) cannot directly handle PDF itself. It uses Ghostscript as its 'delegate' to process input PDF pages and convert them to a series of raster images.

Only then 'identify' gets its turn: it then reports all the many details -- but most of these are details about the newly generated raster image, not about the original PDF. The only items which are appropriate for the input PDF are the few (3-5?) lines (out of almost 300!) reported underneath the 'Properties' line: 'date:create', 'date:modify', 'pdf:Version' and 'signature'. How reliable these are, is doubtful...

So unfortunately, the info you provided does not help much.

There are better (free) command line tools tools to investigate the PDF. First, 'pdfinfo':

Code: Select all

pdfinfo gitdags.pdf 

 Creator:        TeX
 Producer:       pdfTeX-1.40.15
 CreationDate:   Tue Feb  3 17:56:43 2015 
 ModDate:        Tue Feb  3 17:56:43 2015
 Tagged:         no 
 UserProperties: no
 Suspects:       no
 Form:           none
 JavaScript:     no
 Pages:          1
 Encrypted:      no
 Page size:      158.799 x 75.717 pts
 Page rot:       0
 File size:      44261 bytes
 Optimized:      no
 PDF version:    1.5
As you can see, this PDF info is more complete than what you get from 'identify -verbose'. Also, the 'CreationDate' and 'ModDate' metadata do differ from what identify reports... (OK, I tested shortly: `identify` reports the current time as 'date:create' and 'date:modify'. This is plain wrong by identify and has to be regarded as a bug!)

Second, 'pdfimages':

Code: Select all

pdfimages -list gitdags.pdf 

 page   num  type   width height color comp bpc  enc interp  object ID x-ppi y-ppi size ratio
 --------------------------------------------------------------------------------------------
So, no results here. There are no embedded images in the PDF. What we see is vector graphics.

Third, 'pdffonts':

Code: Select all

pdffonts gitdags.pdf
 name                     type    encoding  emb sub uni object ID
 ------------------------ ------- --------- --- --- --- ---------
 APTQJI+LMMono9-Regular   Type 1  Custom    yes yes no      32  0
 NSZVGH+LMMono8-Regular   Type 1  Custom    yes yes no      33  0
Now let's see how ImageMagick processes the PDF:

Code: Select all

convert -verbose gitdags.pdf gitdags.png

 /var/tmp/magick-38522tfS9sU7JKOO01 PNG 159x76 159x76+0+0 8-bit sRGB 5.4KB 0.000u 0:00.000
 gitdags.pdf PDF 159x76 159x76+0+0 16-bit sRGB 5.4KB 0.000u 0:00.000
 gitdags.pdf=>gitdags.png PDF 159x76 159x76+0+0 8-bit sRGB 186c 2.79KB 0.000u 0:00.000
 
 [ghostscript library] -q -dQUIET -dSAFER -dBATCH -dNOPAUSE -dNOPROMPT -dMaxBitmap=500000000 \
    -dAlignToPixels=0 -dGridFitTT=2 "-sDEVICE=pngalpha" -dTextAlphaBits=4 -dGraphicsAlphaBits=4 \
    "-r72x72"  "-sOutputFile=/var/tmp/magick-38522tfS9sU7JKOO0%d" "-f/var/tmp/magick-38522GemGFJkDIY3Z" \
    "-f/var/tmp/magick-38522zBpgqK8MGSKz"
You can clearly see how Ghostscript is at work as ImageMagick's delegate for processing PDF input.

Finally, I did run the conversion with a direct Ghostscript command like so:

Code: Select all

gs -r400 -sDEVICE=pngalpha -o gitdags.png gitdags.pdf
I used different Ghostscript versions: v9.10, v9.15 and a self-compiled v9.16 (from today's Git clone of the Ghostscript sources). I also tried it with different resulutions (up to 1200 PPI!, not just your 400 PPI).

I'm sorry to report: in every single case this results in similar artifacts you you reported.

So this is nothing the ImageMagick developers can do anything about.

Maybe you should report this problem in the Ghostscript bugzilla? ( http://bugs.ghostscript.com/ )

Re: Conversion from PDF to PNG contains unwanted artifacts

Posted: 2015-02-04T16:16:04-07:00
by glennrp
I don't see the artifacts. I'm using IM-6.9.0-4 with libnpg-1.6.16 and (I believe) ghostscript 9.10. I do see drop shadows but I assume those were deliberately included.

Re: Conversion from PDF to PNG contains unwanted artifacts

Posted: 2015-02-04T16:53:37-07:00
by vmrob
pipitas wrote:I'm sorry to report: in every single case this results in similar artifacts you you reported.

So this is nothing the ImageMagick developers can do anything about.

Maybe you should report this problem in the Ghostscript bugzilla? ( http://bugs.ghostscript.com/ )
Thanks for the quick reply! I'll be sure to submit something to Ghostscript for that bug though. I really appreciate the additional debug work you put into it as well. The additional commands are also really helpful; I'll keep those in mind next time I need to debug this sort of thing.
glennrp wrote:I don't see the artifacts. I'm using IM-6.9.0-4 with libnpg-1.6.16 and (I believe) ghostscript 9.10. I do see drop shadows but I assume those were deliberately included.
Would you happen to have an output example? I would really like to see what that looked like.

Re: Conversion from PDF to PNG contains unwanted artifacts

Posted: 2015-02-04T17:25:38-07:00
by glennrp
Here's my output: http://www.simplesystems.org/users/glennrp/im/
Note that the transparency was lost.

EDIT: transparency is not lost. About 5 columns along the left border are fully transparent; all others are opaque.

Re: Conversion from PDF to PNG contains unwanted artifacts

Posted: 2015-02-04T17:39:46-07:00
by vmrob
The artifacts are present in the centers of the arrowheads:

Image

Re: Conversion from PDF to PNG contains unwanted artifacts

Posted: 2015-02-04T17:46:04-07:00
by glennrp
OK I do see those. I thought they were put there on purpose.

Re: Conversion from PDF to PNG contains unwanted artifacts

Posted: 2015-02-04T17:47:34-07:00
by vmrob
glennrp wrote:OK I do see those. I thought they were put there on purpose.
Nope. I know it's a little small, but this is the reference pdf: https://s3.amazonaws.com/vmrob/imagemag ... itdags.pdf

Re: Conversion from PDF to PNG contains unwanted artifacts

Posted: 2015-02-04T17:56:38-07:00
by glennrp
I added a -density 4800 closeup of one of the arrowheads to the above-mentioned web page. It does look to me as though the little triangle was deliberately drawn there.

Re: Conversion from PDF to PNG contains unwanted artifacts

Posted: 2015-02-05T08:43:37-07:00
by pipitas
glennrp wrote:I added a -density 4800 closeup of one of the arrowheads to the above-mentioned web page. It does look to me as though the little triangle was deliberately drawn there.
If so, then all the PDF viewers I tested[*][/color][/b] the input PDF with (apart from Ghostscript-based 'gv'), do have the same bug: because these do not show this intentional 'artifacts', not even with their respective maximum zoom-in level. Likely?!?

(I still have to test with Acrobat...)

[*]:[/b][/color] These were: Chrome's builtin PDF viewer, Firefox with PDF.js, evince, XPDF, Preview.app, MuPDF -- all on Mac OS X.

Re: Conversion from PDF to PNG contains unwanted artifacts

Posted: 2015-02-05T09:11:13-07:00
by snibgo
Adobe Reader 11.0.6 does not show white outlined triangles. The arrowheads show as solid gray.

Re: Conversion from PDF to PNG contains unwanted artifacts

Posted: 2015-02-05T11:26:15-07:00
by fmw42
For me, Mac Preview on OSX 10.6.8 (snow leopard) does not show the white triangles in the middle of arrow heads for the original PDF file. It does not show in my Safari browser 5.1.10 either, nor in my Acrobat Reader 11.

Re: Conversion from PDF to PNG contains unwanted artifacts

Posted: 2015-02-05T11:50:48-07:00
by pipitas
It's clear then: a Ghostscript bug.

Re: Conversion from PDF to PNG contains unwanted artifacts

Posted: 2015-02-05T12:11:51-07:00
by pipitas
I tested a few more (direct) Ghostscript-conversions to raster formats: '-sDEVICE={tiff24nc,png16m,jpeg}'. All these didn't produce the artifact. It's only the 'pngalpha'-device which has the problem.

Maybe this is a chance to find a workaround?[*][/b][/color]

Provided, your IM has a setup which does not go through Ghostscript's 'pngalpha' device when converting to TIFF in the first stage:

Code: Select all

convert -verbose -density 400 gitdag.pdf gitdag.tiff

convert gitdag.tiff gitdag.png
You can check your specific delegates setup for PDF processing like this:

Code: Select all

convert -list delegate | grep pdf
Check here how you can change or add your own delegate setup: If this isn't possible, you'll need to run a Ghostscript command first:

Code: Select all

gs -o gitdag.tiff -r400x400 -sDEVICE=tiff32nc gitdag.pdf

convert gitdag.tiff gitdag.png
I hope one of these approaches will work for you.

[*][/b][/color] (It may be quite a long time before a GS bugfix arrives in user space for this specific problem...)

Re: Conversion from PDF to PNG contains unwanted artifacts

Posted: 2016-01-23T21:26:25-07:00
by aaron.cuffman
pipitas wrote:I tested a few more (direct) Ghostscript-conversions to raster formats: '-sDEVICE={tiff24nc,png16m,jpeg}'. All these didn't produce the artifact. It's only the 'pngalpha'-device which has the problem.
I've come from the future to thank you. Thanks! I'm a noob with Ghostscript and had no clue why my images had those crappy artifacts. I was using Png256 and simply switching to Png16m fixed the issue completely. Again, thank you!