Shell – Convert ppt to jpg

The desired result can also be achieved without proprietary tools. If you have GhostScript installed, you can convert your PDF presentation into a set of JPG images using:

gs -dNOPAUSE -dBATCH -dSAFER -dGraphicsAlphaBits=4 -dTextAlphaBits=4 -sDEVICE=jpeg -r300 -sOutputFile='page-%00d.jpg' YOURFILE.pdf

Then, with the plugin for OpenOffice/LibreOffice create a presentation where each image fills exactly one slide. You can also easily keep the order of the pages by choosing the plugin option "natural sorting".

I have written an article on the topic in my blog, unfortunately in German only.

Edit: Fixed some issues with the original script. Added an alternative one based on Marcks Thomas' proposition.

Edit 2: Updated cutoff values based on a number of test runs. I am still not sure how to estimate file sizes for greyscale images. If you are working with a large number of images outside of RGB colour schemes you might want to implement the first script as a fallback mode to the second one.

Edit 3: Added optipng integration. This optimizes PNG file sizes without any quality loss. See here for more information. Some smaller improvements.

Version 0.1

Important note: This script is deprecated. Newer versions are far more efficient.

Alright, my question might have been slightly too localized, so I put some time into it and compiled the script myself:

#!/bin/bash

# AUTHOR:   (c) MHC (http://askubuntu.com/users/81372/mhc)
# NAME:     Intelliconvert 0.1
# DESCRIPTION:  A script to automate and optimize the choice between different image formats.
# LICENSE:  GNU GPL v3 (http://www.gnu.org/licenses/gpl.html)
# REQUIREMENTS:  Imagemagick

ORIGINAL="$1"

###Filetype check###

MIME=$(file -ib "$ORIGINAL")

if [ "$MIME" = "image/png; charset=binary" ]
  then
    echo "PNG Mode"

###Variables###

      ##Original Image##
    FILENAME=$(basename "$ORIGINAL")
    PARENTDIR=$(dirname "$ORIGINAL")
        SUBFOLDER=$(echo "$PARENTDIR" | cut -d"/" -f10-)
    ORIGARCHIVE="~/ORIG"

      ##Converted Image##
    TEMPDIR="/tmp/imgcomp"
    CONVERTED="$TEMPDIR/$FILENAME.jpg"

      ##Image comparison##
    DIFFLO="50"
    DIFFHI="75"
    CUTOFF="1000000"

      ##DEBUG
    echo "#### SETTINGS ####"
    echo "Filepath to original = $ORIGINAL"
    echo "Filename= $FILENAME"
    echo "Parent directory = $PARENTDIR"
    echo "Archive directory = $ORIGARCHIVE"
    echo "Temporary directory = $TEMPDIR"
    echo "Filepath to converted image = $CONVERTED"
    echo "Low cut-off = $DIFFLO"
    echo "High cut-off = $DIFFHI"

###Conversion###

    convert -quality 92 -flatten -background white "$ORIGINAL" "$CONVERTED"

###Comparison###

    F1=$(stat -c%s "$ORIGINAL" )
    F2=$(stat -c%s "$CONVERTED" )
    FQ=$(echo "($F2*100/$F1)" | bc)

      #Depending on filesize we use a different Cut-off#
    if [ "$F1" -ge "$CUTOFF" ]
      then
        DIFF="$DIFFHI"
      else  
        DIFF="$DIFFLO"
    fi

      ##DEBUG
    echo "### COMPARISON ###"
    echo "Filesize original = $F1 Bytes"
    echo "Filesize converted = $F2 Bytes"
    echo "Chosen cut-off = $DIFF %"
    echo "Actual Ratio = $FQ %"


    if [ "$FQ" -le "$DIFF" ]
      then
           echo "JPEG is more efficient, converting..."
           mv -v "$CONVERTED" "$PARENTDIR"
               mkdir -p "$ORIGARCHIVE/$SUBFOLDER"
           mv -v "$ORIGINAL" "$ORIGARCHIVE/$SUBFOLDER"
      else
           echo "PNG is fine, exiting."
           rm -v "$CONVERTED"
    fi


  else
    echo "File does not exist or unknown MIME type, exiting."

fi

The script works great in combination with Watcher.

This is my first proper script, so there might be some unresolved bugs and issues I just didn't see. Feel free to use it for yourself and improve it. If you do so, I'd appreciate it if you could leave a comment here, so that I can learn from it.

Version 0.2.1

A more efficient way of finding the right format can be achieved by comparing the original's file size to its estimated size as an uncompressed image:

#!/bin/bash

# AUTHOR:   (c) MHC (http://askubuntu.com/users/81372/mhc)
# NAME:     Intelliconvert 0.2.1
# DESCRIPTION:  A script to automate and optimize the choice between different image formats.
# LICENSE:  GNU GPL v3 (http://www.gnu.org/licenses/gpl.html)
# REQUIREMENTS:  Imagemagick, Optipng

################ Filetype Check#################

MIME=$(file -ib "$1")

if [ "$MIME" = "image/png; charset=binary" ]
  then
    echo "###PNG Mode###"

####################Settings####################

##Folders##
ORIGARCHIVE="~/ORIG"

##Comparison##
DIFFLO="25"
DIFFHI="20"
CUTOFF="1000000"

################################################

###Variables###

ORIGINAL="$1"
FILENAME=$(basename "$ORIGINAL")
PARENTDIR=$(dirname "$ORIGINAL")
SUBFOLDER=$(echo "$PARENTDIR" | cut -d"/" -f10-)
CONVERTED="$PARENTDIR/$FILENAME.jpg"

#DEBUG#
    echo "###SETTINGS###"
    echo "Filepath to original = $ORIGINAL"
    echo "Filename= $FILENAME"
    echo "Parent directory = $PARENTDIR"
    echo "Archive directory = $ORIGARCHIVE"
    echo "Filepath to converted image = $CONVERTED"
    echo "Low cut-off = $DIFFLO"
    echo "High cut-off = $DIFFHI"


###Image data###

        WIDTH=$(identify -format "%w" "$ORIGINAL")
        HEIGHT=$(identify -format "%h" "$ORIGINAL")
        ZBIT=$(identify -format "%z" "$ORIGINAL")
        COL=$(identify -format "%[colorspace]" "$ORIGINAL")
        F1=$(stat -c%s "$ORIGINAL")

        if [ "$COL" = "RGB" ]
          then
              CHANN="3"
          else
              CHANN="1"
        fi


###Cutoff setting###

    if [ "$F1" -ge "$CUTOFF" ]
      then
        DIFF="$DIFFHI"
      else  
        DIFF="$DIFFLO"
    fi


###Calculations on uncompressed image###

        BMPSIZE=$(echo "($WIDTH*$HEIGHT*$ZBIT*$CHANN/8)" | bc)
        FR=$(echo "($F1*100/$BMPSIZE)" | bc)

#DEBUG#

        echo "###IMAGE DATA###"
        echo "Image Dimensions = $WIDTH x $HEIGHT"
        echo "Colour Depth = $ZBIT"
        echo "Colour Profile = $COL"
        echo "Channels = $CHANN"
        echo "Estimated uncompressed size = $BMPSIZE"
        echo "Actual file size = $F1"
        echo "Estimated size ratio = $FR %"
        echo "Cutoff at $DIFF %"

###Backup###

        echo "###BACKUP###"
        mkdir -p "$ORIGARCHIVE/$SUBFOLDER"  #keep the original folder structure
        cp -v "$ORIGINAL" "$ORIGARCHIVE/$SUBFOLDER"
        echo ""

###Comparison###

    if [ "$FR" -ge "$DIFF" ]
      then
          echo "JPEG is more efficient, converting..."
          convert -quality 92 -flatten -background white "$ORIGINAL" "$CONVERTED"
              echo "Done."
          echo "Cleaning up..."
          rm -v "$ORIGINAL"
      else
          echo "PNG is fine, passing over to optipng."
              echo "Optimizing..."
              optipng "$ORIGINAL"
              echo "Done."
    fi

################ Filetype Check#################

  else
    echo "File does not exist or unknown MIME type, exiting."

fi

Props to @Marcks Thomas for the great idea.