Category: Ubuntu

OCR Text from PDF Document

✎ Last updated on 2014-07-11 at 12:40 EDT

Today, I had to convert a scanned 3-page PDF file back into a editable document. So, open source software to the rescue. I was able to complete the task with the help of:

  • tesseract — for OCR, and
  • imagemagick — for converting PDF pages to an image format that tesseract accepts.

  1. Installing the software

    sudo apt-get -y install tesseract-ocr imagemagick

  2. Convert PDF pages to image

    convert -density 300 -depth 8 scan.pdf[0] scan0.png
convert -density 300 -depth 8 scan.pdf[1] scan1.png
convert -density 300 -depth 8 scan.pdf[2] scan2.png

    convert is a member of the amagemagick tools. You can use it to convert between image formats as well as resize an image, blur, crop, despeckle, dither, draw on, flip, join, re-sample, and much more.

    Here, I’m only using two options:

    -density width
    to set the resolution of an image for rendering to devices. The default unit of measure is dots per inch. The default resolution is 72 dpi.

    -depth value
    to set the number of bits in a color sample within a pixel.

    The numbers between the brackets mark the page in the PDF document to be converted. Of course, as any programmer can tell you, you start counting at zero.

  3. OCR page images to text

    $ tesseract scan0.png scan0.txt
Tesseract Open Source OCR Engine v3.02.01 with Leptonica
$ tesseract scan1.png scan1.txt
Tesseract Open Source OCR Engine v3.02.01 with Leptonica
$ tesseract scan2.png scan2.txt
Tesseract Open Source OCR Engine v3.02.01 with Leptonica

And then just copy the OCR text from the text files into a new document to clear up any typo and reformat the document.

dircolors for better ls listing

✎ Last updated on 2014-12-25 at 22:07 EST

ls uses the environment variable LS_COLORS to determine the colors in which the filenames are to be displayed. This environment variable is usually set by a command in the .bashrc file like
eval 'dircolors some_path/dir_colors'
to create a customize .dircolors file, use the command

dircolors -p > .dircolors

and then edit the .dircolors file.

for example, change the color of execute permission to red with: EXEC 00;31

The comments in the generated .dircolors file already listed the color codes.
ISO 6429 color sequences are composed of sequences of numbers separated by semicolons. The most common codes are:

Attribute Codes:
00 none — to restore default color
01 bold — for brighter colors
04 underscore — for underlined text
05 blink — for flashing text
07 reverse — to reverse background and foreground colors
08 concealed — to hide text
Text Color Codes: Background Color Codes
30 for black foreground 40 for black background
31 for red foreground 41 for red background
32 for green foreground 42 for green background
33 for orange foreground 43 for brown background
34 for blue foreground 44 for blue background
35 for purple foreground 45 for purple background
36 for cyan foreground 46 for cyan background
37 for gray foreground 47 for gray background
Extra Text Color Codes: Extra Background Color Codes
90 dark gray 100 dark gray background
91 light red 101 light red background
92 light green 102 light green background
93 yellow 103 yellow background
94 light blue 104 light blue background
95 light purple 105 light purple background
96 turquoise 106 turquoise background
97 white 107 white background

Adding Desktop Entries to System

Desktop entry files provide information about item in menus.

Desktop entry files must reside in the $XDG_DATA_DIRS/applications directory and must have a .desktop file extension. If $XDG_DATA_DIRS is not set, then the default path is /usr/share is used.

User specific desktop entries may be located at $XDG_DATA_HOME/applications which is searched first. If $XDG_DATA_HOME is not set, then the default path ~/.local/share is used. Desktop entries are collected from all directories in the $XDG_DATA_DIRS environment variable. Directories which appear first in $XDG_DATA_DIRS are given precedence when there are several .desktop files with the same name.

So, if you drop a correctly formatted .desktop file in any of the above mentioned locations, a new launcher icon will appear in the menu hierarchy as specified by the keywords in the .desktop file.

The freedesktop.org maintains software base platform and specification for desktop software on Linux and UNIX. To get more information on the latest desktop entry files, see the Desktop Entry Specification at freedesktop.org.

Here’s a sample desktop entry file for Eclipse:

[Desktop Entry]
Version=1.0
Name=Eclipse
GenericName=Eclipse IDE
Comment=Eclipse IDE
Exec=/home/puppychau/bin/eclipse/eclipse %F
Icon=/home/puppychau/bin/eclipse/icon.xpm
Type=Application
Terminal=false
Categories=Development;IDE