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Making thumbnails efficiently with ghostscript
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bugbear
May 22, 2012, 9:05:50 AM5/22/12
to
(I've asked this before, but the thread fizzled)
http://groups.google.com/group/comp.lang.postscript/browse_thread/thread/ca973ffaf885834c/56f107d7b68ee435?hl=en#56f107d7b68ee435
I would like to use ghostscript to make a thumbnail of the first page of a PDF file,
or an EPSF file, to the following spec.
* The thumbnail must have the SAME aspect ratio as the original
* the size of the longest side of the thumbnail must be 128 pixels
The correct pixels can be easily made, by simply rendering at a "too-high"
resolution, and then using ImageMagick:
convert <raster> -resize 128x128 <thuumbnail>
But this can be resource hungry for large media sources. Setting the
resolution high enough to get good thumbs for tiny images
(e.g. a business card image) leaves the resolution FAR
too high for large images (like a newspaper page).
Using info from the previous thread the closest approach is to use these flags:
-r72 -dDEVICEWIDTHPOINTS=128 -dDEVICEHEIGHTPOINTS=128 -dPDFFitPage -dEPSFitPage
Which gives me a 128x128 raster every time. But if the aspect ratio
of the original is NOT 1:1, I either get white padding
on the right, or white padding on the top.
Can anyone suggest a way to get my "dream" thumbnail,
i.e. the same pixels as I'm currently getting, but with
no padding?
The closest I can get at the moment is a second pass with ImageMagick using
options to trim any exterior whitespace
-bordercolor white -border 1x1 -trim +repage
But this will remove any peripheral white
*content* as well as the white padding from the rendering.
All help welcomed (and I bet I'm not the only one wanting this)
BugBear
http://groups.google.com/group/comp.lang.postscript/browse_thread/thread/ca973ffaf885834c/56f107d7b68ee435?hl=en#56f107d7b68ee435
I would like to use ghostscript to make a thumbnail of the first page of a PDF file,
or an EPSF file, to the following spec.
* The thumbnail must have the SAME aspect ratio as the original
* the size of the longest side of the thumbnail must be 128 pixels
The correct pixels can be easily made, by simply rendering at a "too-high"
resolution, and then using ImageMagick:
convert <raster> -resize 128x128 <thuumbnail>
But this can be resource hungry for large media sources. Setting the
resolution high enough to get good thumbs for tiny images
(e.g. a business card image) leaves the resolution FAR
too high for large images (like a newspaper page).
Using info from the previous thread the closest approach is to use these flags:
-r72 -dDEVICEWIDTHPOINTS=128 -dDEVICEHEIGHTPOINTS=128 -dPDFFitPage -dEPSFitPage
Which gives me a 128x128 raster every time. But if the aspect ratio
of the original is NOT 1:1, I either get white padding
on the right, or white padding on the top.
Can anyone suggest a way to get my "dream" thumbnail,
i.e. the same pixels as I'm currently getting, but with
no padding?
The closest I can get at the moment is a second pass with ImageMagick using
options to trim any exterior whitespace
-bordercolor white -border 1x1 -trim +repage
But this will remove any peripheral white
*content* as well as the white padding from the rendering.
All help welcomed (and I bet I'm not the only one wanting this)
BugBear
Thomas Kaiser
May 22, 2012, 10:11:25 AM5/22/12
to
["Followup-To:" comp.text.pdf]
bugbear wrote in <news:PKKdnck_eruzEibS...@brightview.co.uk>
to get the approriate resolution for an image with at least 256x256
pixels and then use this as $MyRenderResolution. This
gs -dUseTrimBox -q -dBATCH -dNOPAUSE -r${MyRenderResolution} \
-sDEVICE=... -dDOINTERPOLATE -dTextAlphaBits=4 -dGraphicsAlphaBits=4 \
-dMaxBitmap=100000000 -dMaxPatternBitmap=2000000 -sOutputFile=... \
-c 100000000 setvmthreshold -f /path/to/pdf
will produce an image with correct aspect ratio (-dTextAlphaBits=2 and
-dGraphicsAlphaBits=2 should work a bit faster without decreasing
rendering quality since you get an image with twice the pixel dimensions
as necessary).
When you scale down using ImageMagic in a second step you can then apply
some slight sharping or unsharp masking which will produce superiour
results.
Regards,
Thomas
bugbear wrote in <news:PKKdnck_eruzEibS...@brightview.co.uk>
> I would like to use ghostscript to make a thumbnail of the first page of a PDF file,
> or an EPSF file, to the following spec.
>
> * The thumbnail must have the SAME aspect ratio as the original
> * the size of the longest side of the thumbnail must be 128 pixels
>
> The correct pixels can be easily made, by simply rendering at a
> "too-high" resolution, and then using ImageMagick:
Use the dimensions of the trimbox (or mediabox if missing), do some math
> or an EPSF file, to the following spec.
>
> * The thumbnail must have the SAME aspect ratio as the original
> * the size of the longest side of the thumbnail must be 128 pixels
>
> The correct pixels can be easily made, by simply rendering at a
> "too-high" resolution, and then using ImageMagick:
to get the approriate resolution for an image with at least 256x256
pixels and then use this as $MyRenderResolution. This
gs -dUseTrimBox -q -dBATCH -dNOPAUSE -r${MyRenderResolution} \
-sDEVICE=... -dDOINTERPOLATE -dTextAlphaBits=4 -dGraphicsAlphaBits=4 \
-dMaxBitmap=100000000 -dMaxPatternBitmap=2000000 -sOutputFile=... \
-c 100000000 setvmthreshold -f /path/to/pdf
will produce an image with correct aspect ratio (-dTextAlphaBits=2 and
-dGraphicsAlphaBits=2 should work a bit faster without decreasing
rendering quality since you get an image with twice the pixel dimensions
as necessary).
When you scale down using ImageMagic in a second step you can then apply
some slight sharping or unsharp masking which will produce superiour
results.
Regards,
Thomas
bugbear
May 22, 2012, 10:19:22 AM5/22/12
to
Thomas Kaiser wrote:
> ["Followup-To:" comp.text.pdf]
> bugbear wrote in<news:PKKdnck_eruzEibS...@brightview.co.uk>
>> I would like to use ghostscript to make a thumbnail of the first page of a PDF file,
>> or an EPSF file, to the following spec.
>>
>> * The thumbnail must have the SAME aspect ratio as the original
>> * the size of the longest side of the thumbnail must be 128 pixels
>>
>> The correct pixels can be easily made, by simply rendering at a
>> "too-high" resolution, and then using ImageMagick:
>
> Use the dimensions of the trimbox (or mediabox if missing), do some math
> to get the approriate resolution for an image with at least 256x256
> pixels and then use this as $MyRenderResolution. This
OK - any recommendation for "getting the trimbox/mediabox/cropbox"
> ["Followup-To:" comp.text.pdf]
> bugbear wrote in<news:PKKdnck_eruzEibS...@brightview.co.uk>
>> I would like to use ghostscript to make a thumbnail of the first page of a PDF file,
>> or an EPSF file, to the following spec.
>>
>> * The thumbnail must have the SAME aspect ratio as the original
>> * the size of the longest side of the thumbnail must be 128 pixels
>>
>> The correct pixels can be easily made, by simply rendering at a
>> "too-high" resolution, and then using ImageMagick:
>
> Use the dimensions of the trimbox (or mediabox if missing), do some math
> to get the approriate resolution for an image with at least 256x256
> pixels and then use this as $MyRenderResolution. This
efficiently, in a perl or shell script? You're quite
right that this would work, of course.
Thomas Kaiser
May 22, 2012, 11:34:32 AM5/22/12
to
bugbear schrieb in <news:bsSdncge-572PSbS...@brightview.co.uk>
one from XPDF [2] with the "-box" parameter.
The values you get are in PostScript points (1/72 inch) and in this
order: x/y of the lower left corner and x/y of the upper right.
'pdfinfo -box' might produce this:
Title: 27491-0_Agassi_Open_komplett.indd
Author: kbauer
Creator: Adobe InDesign CS3 (5.0.4)
Producer: Acrobat Distiller 9.0.0 (Macintosh)
CreationDate: Fri Sep 25 10:45:07 2009
ModDate: Thu Nov 5 15:04:54 2009
Tagged: no
Pages: 1
Encrypted: no
Page size: 403.139 x 618.095 pts
MediaBox: 920.82 29.03 1323.96 647.12
CropBox: 920.82 29.03 1323.96 647.12
BleedBox: 920.82 29.03 1323.96 647.12
TrimBox: 920.82 29.03 1323.96 647.12
ArtBox: 920.82 29.03 1323.96 647.12
File size: 17634656 bytes
Optimized: yes
PDF version: 1.6
To calculate the dimensions of the TrimBox in pts all you have to do is
to subtract value 3 - 1 (x axis) and 4 -1 (y axis). To translate to inch
simply divide by 72. In a shell script one could use in two steps:
MyXAxis=$(pdfinfo -box "${MyPDF}" | grep "^TrimBox" | awk -F" " '{print "("$4" - "$2") / 72"}' | bc -l)
MyYAxis=$(pdfinfo -box "${MyPDF}" | grep "^TrimBox" | awk -F" " '{print "("$5" - "$3") / 72"}' | bc -l)
echo "TrimBox dimensions in inch: ${MyXAxis} x ${MyYAxis}"
The result would be:
TrimBox dimensions in inch: 5.59916666666666666666 x 8.58458333333333333333
Use the larger value of both and do the division. But don't forget to
increment the value by 1 before using it with gs's "-r" switch:
MyRenderResolution=$(( 1 + $(echo 256 / ${MyYAxis} | bc) ))
This will ensure that you have at least twice the pixels needed for
downscaling to 128 pixels (applying some sharpening [3])
Regards,
Thomas
[1] http://www.helios.de/web/EN/products/HELIOS-PDF-HandShake.html?lang_id=en
[2] http://www.foolabs.com/xpdf/
[3] http://redskiesatnight.com/2005/04/06/sharpening-using-image-magick/
> Thomas Kaiser wrote:
>> ["Followup-To:" comp.text.pdf]
>> bugbear wrote in<news:PKKdnck_eruzEibS...@brightview.co.uk>
>>> I would like to use ghostscript to make a thumbnail of the first
>>> page of a PDF file, or an EPSF file, to the following spec.
>>>
>>> * The thumbnail must have the SAME aspect ratio as the original
>>> * the size of the longest side of the thumbnail must be 128 pixels
>>>
>>> The correct pixels can be easily made, by simply rendering at a
>>> "too-high" resolution, and then using ImageMagick:
>>
>> Use the dimensions of the trimbox (or mediabox if missing), do some
>> math to get the approriate resolution for an image with at least
>> 256x256 pixels and then use this as $MyRenderResolution. This
>
> OK - any recommendation for "getting the trimbox/mediabox/cropbox"
> efficiently, in a perl or shell script?
In our workflows we use Helios' pdfinfo [1]. But you could also use the
>> ["Followup-To:" comp.text.pdf]
>> bugbear wrote in<news:PKKdnck_eruzEibS...@brightview.co.uk>
>>> I would like to use ghostscript to make a thumbnail of the first
>>> page of a PDF file, or an EPSF file, to the following spec.
>>>
>>> * The thumbnail must have the SAME aspect ratio as the original
>>> * the size of the longest side of the thumbnail must be 128 pixels
>>>
>>> The correct pixels can be easily made, by simply rendering at a
>>> "too-high" resolution, and then using ImageMagick:
>>
>> Use the dimensions of the trimbox (or mediabox if missing), do some
>> math to get the approriate resolution for an image with at least
>> 256x256 pixels and then use this as $MyRenderResolution. This
>
> OK - any recommendation for "getting the trimbox/mediabox/cropbox"
> efficiently, in a perl or shell script?
one from XPDF [2] with the "-box" parameter.
The values you get are in PostScript points (1/72 inch) and in this
order: x/y of the lower left corner and x/y of the upper right.
'pdfinfo -box' might produce this:
Title: 27491-0_Agassi_Open_komplett.indd
Author: kbauer
Creator: Adobe InDesign CS3 (5.0.4)
Producer: Acrobat Distiller 9.0.0 (Macintosh)
CreationDate: Fri Sep 25 10:45:07 2009
ModDate: Thu Nov 5 15:04:54 2009
Tagged: no
Pages: 1
Encrypted: no
Page size: 403.139 x 618.095 pts
MediaBox: 920.82 29.03 1323.96 647.12
CropBox: 920.82 29.03 1323.96 647.12
BleedBox: 920.82 29.03 1323.96 647.12
TrimBox: 920.82 29.03 1323.96 647.12
ArtBox: 920.82 29.03 1323.96 647.12
File size: 17634656 bytes
Optimized: yes
PDF version: 1.6
To calculate the dimensions of the TrimBox in pts all you have to do is
to subtract value 3 - 1 (x axis) and 4 -1 (y axis). To translate to inch
simply divide by 72. In a shell script one could use in two steps:
MyXAxis=$(pdfinfo -box "${MyPDF}" | grep "^TrimBox" | awk -F" " '{print "("$4" - "$2") / 72"}' | bc -l)
MyYAxis=$(pdfinfo -box "${MyPDF}" | grep "^TrimBox" | awk -F" " '{print "("$5" - "$3") / 72"}' | bc -l)
echo "TrimBox dimensions in inch: ${MyXAxis} x ${MyYAxis}"
The result would be:
TrimBox dimensions in inch: 5.59916666666666666666 x 8.58458333333333333333
Use the larger value of both and do the division. But don't forget to
increment the value by 1 before using it with gs's "-r" switch:
MyRenderResolution=$(( 1 + $(echo 256 / ${MyYAxis} | bc) ))
This will ensure that you have at least twice the pixels needed for
downscaling to 128 pixels (applying some sharpening [3])
Regards,
Thomas
[1] http://www.helios.de/web/EN/products/HELIOS-PDF-HandShake.html?lang_id=en
[2] http://www.foolabs.com/xpdf/
[3] http://redskiesatnight.com/2005/04/06/sharpening-using-image-magick/
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