I want to apply some improvements (change brightness, contrast, etc) to a pdf, to make it more readable, so I chose ImageMagick and pdftk. I used the following command to split the pdf into several single page pdf files, so I can operate with ImageMagick one file at a time.
pdftk a.pdf burst output %04d.pdf
At this time, everything is ok. I take one of these files (eg. 0038.pdf) to make my tests. For example, to adjust the contrast I used this command:
convert 0038.pdf -quality 100 -density 300 -brightness-contrast 0x10% out.pdf
But this is the result:
ORIGINAL
CONVERTED
I tried to change the value of quality, density, size, resize, geometry and the output pdf has different size/resolution, but is always unreadable. So I realized that the problem is upstream of the conversion. It seems like the input pdf size and resolution are read wrongly from convert
.
Infact, when I just type this command:
convert -verbose 0038.pdf out.pdf
I get:
/tmp/magick-9894W9c_JPl1I7QV1 PNG 380x482 380x482+0+0 8-bit sRGB 128KB 0.010u 0:00.010
0038.pdf PNG 380x482 380x482+0+0 16-bit sRGB 128KB 0.000u 0:00.000
0038.pdf=>out.pdf PNG 380x482 380x482+0+0 16-bit sRGB 125KB 0.050u 0:00.049
[ghostscript library] -q -dQUIET -dSAFER -dBATCH -dNOPAUSE -dNOPROMPT -dMaxBitmap=500000000 -dAlignToPixels=0 -dGridFitTT=2 "-sDEVICE=pngalpha" -dTextAlphaBits=4 -dGraphicsAlphaBits=4 "-r72x72" "-sOutputFile=/tmp/magick-9894W9c_JPl1I7QV%d" "-f/tmp/magick-9894s1cR4gD9oYuz" "-f/tmp/magick-9894KMmuVq0n9U8c"
As you can see, the size is 380 x 482, but I know that the real size is 1653 x 2338 pixels.
This is the metadata of 0038.pdf (read with exiftool
)
ExifToolVersion = 9.70
FileName = 0038.pdf
Directory = .
FileSize = 429577
FileModifyDate = 1414935360
FileAccessDate = 1414935693
FileInodeChangeDate = 1414935693
FilePermissions = 33188
FileType = PDF
MIMEType = application/pdf
PDFVersion = 1.4
Linearized = false
PDF dictionary (1 of 1) with 4 entries:
0) Info (SubDirectory) -->
+ [Info directory with 5 entries]
| 0) ModifyDate = (D:20141101192012Z)
| 1) CreateDate = (D:20141101192012Z)
| 2) Title = 0038
| 3) Creator = (pdftk 2.02 - www.pdftk.com)
| 4) Producer = (itext-paulo-155 \(itextpdf.sf.net-lowagie.com\))
1) ID = [<e5af52575d23dc1a2aca80f7453fa203>,<4cc6d7fb99aca8c755033ca2973b713c>]
2) Root (SubDirectory) -->
+ [Root directory with 3 entries]
| 0) Metadata (SubDirectory) -->
| + [Metadata directory with 3 entries]
| | 0) Subtype = /XML
| | 1) Type = /Metadata
| | 2) Length = 3008
| | + [XMP directory, 3008 bytes]
| | | XMPToolkit = Image::ExifTool 9.70
| | | Title = 0038
| | | Artist = A
| 1) Type = /Catalog
| 2) Pages (SubDirectory) -->
| + [Pages directory with 3 entries]
| | 0) Kids (SubDirectory) -->
| | + [Kids directory with 7 entries]
| | | 0) Resources (SubDirectory) -->
| | | + [Resources directory with 2 entries]
| | | | 0) ProcSet = [/PDF,/Text,/ImageB,/ImageC,/ImageI]
| | | | 1) XObject (SubDirectory) -->
| | | | + [XObject directory with 1 entries]
| | | | | 0) JI19a (SubDirectory) -->
| | | | | + [JI19a directory with 9 entries]
| | | | | | 0) Subtype = /Image
| | | | | | 1) Name = /JI19a
| | | | | | 2) Type = /XObject
| | | | | | 3) Width = 1653
| | | | | | 4) Filter = /DCTDecode
| | | | | | 5) Height = 2338
| | | | | | 6) BitsPerComponent = 8
| | | | | | 7) Length = 425229
| | | | | | 8) ColorSpace = /DeviceGray
| | | 1) Rotate = 90
| | | 2) Parent = ref(1 0 R)
| | | 3) Contents (SubDirectory) -->
| | | + [Contents directory with 1 entries]
| | | | 0) Length = 57
| | | 4) Type = /Page
| | | 5) MediaBox = [22,440,504,820]
| | | 6) CropBox = [22,440,504,820]
| | 1) Type = /Pages
| | 2) PageCount = 1
3) Size = 10
Any ideas?