generate_thumbnails.sh

#!/bin/sh

# Proper function of this script on Mac requires:
# install tiff 3.6.1 or newer http://www.libtiff.org/
# brew install ghostscript
# brew install imagemagick

timer()
{
    if [[ $# -eq 0 ]]; then
        echo $(date '+%s')
    else
        local  stime=$1
        etime=$(date '+%s')

        if [[ -z "$stime" ]]; then stime=$etime; fi

        dt=$((etime - stime))
        ds=$((dt % 60))
        dm=$(((dt / 60) % 60))
        dh=$((dt / 3600))
        printf '%d:%02d:%02d' $dh $dm $ds
    fi
}

T=$(timer)

find sku_images -name '*.1' | while read f
do
error=""
filename="$(basename "$f" ".1")"

# Filenames could conflict since cropping duplicates file outputs.
# When faced with 1032522.1 and 1032522t.1, the former is used, second ignored.
if [ ! -f "sku_jpg/$filename.jpg" ]; then
    # A grep for "TRUEVISION-XFILE" is not reliable to discover TGA.
    # Default to TGA since that is the standard format and doens't
    # necessarily have any binary identifiers to grep for.
    # Note, "Paint Shop Pro" can also appear in TGA files.
    error=$(convert -quiet -quality 100 -alpha off -density 200x200 -comment "Converted and resized using Imagemagick 6.8.0 from TGA format by Classic Graphics." -resize '100x100>' tga:"sku_images/$filename.1" "sku_jpg/$filename.jpg" 2>&1 >/dev/null)

    # An error with this message probably means alternate formatting, not TGA.
    # convert: improper image header
    if [[ $error =~ "improper image header" ]]; then
        if [[ $(grep -ce "^CPT7FILE" "$f") -ne 0 ]]; then
            # grep "CPT7FILE" for Corel Draw files. see 1333859.1
            echo "$filename.1 is an unsupported Corel Photo-Paint file and was not converted."

        elif [[ $(grep -ce "Paint Shop Pro Image File" "$f") -ne 0 ]]; then
            # grep "Paint Shop Pro Image File" for unsupported PSP. see 2026216.1
            echo "$filename.1 is an unsupported Paint Shop Pro file and was not converted."

        elif [[ $(grep -ce "^GIF89a" "$f") -ne 0 ]]; then
            # grep at the file head for "GIF89a". see 2156309.1
            convert -quiet -quality 100 -alpha off -density 200x200 -comment "Converted and resized from GIF89a using Imagemagick 6.8.0 by Classic Graphics." -resize '100x100>' gif:"sku_images/$filename.1" "sku_jpg/$filename.jpg"

        elif [[ $(grep -ce "^II" "$f") -ne 0 ]]; then
            # grep "II" meaning TIFF. see 2602091.1
            convert -quiet -quality 100 -alpha off -density 200x200 -comment "Converted and resized from TIFF using Imagemagick 6.8.0 by Classic Graphics." -resize '100x100>' tiff:"sku_images/$filename.1" "sku_jpg/$filename.jpg"

        elif [[ $(grep -ce "^BM" "$f") -ne 0 ]]; then
            # grep "BM" at the start of the file to detect BMP. see 2041952.1
            convert -quiet -quality 100 -alpha off -density 200x200 -comment "Converted and resized from BMP using Imagemagick 6.8.0 by Classic Graphics." -resize '100x100>' bmp:"sku_images/$filename.1" "sku_jpg/$filename.jpg"

        else
            # grep "JFIF" to discover JPEG files. see 0618015.1
            # also look for for "LEAD Technologies"
            # or "ˇÿˇ" at the head of the file
            # JFIF is also found in PSP files, so this must be after that check.
            # JFIF and LEAD aren't always in JPEG files.
            # grep has trouble with "ˇÿˇ"
            # Just try it and output if there's an error.
            error=$(convert -quiet -quality 100 -alpha off -density 200x200 -comment "Resized using Imagemagick 6.8.0 by Classic Graphics." -resize '100x100>' jpeg:"sku_images/$filename.1" "sku_jpg/$filename.jpg" 2>&1 >/dev/null)
            if [[ $error -ne "" ]]; then
                echo "$filename.1 is an unknown filetype and was not converted."
            fi
        fi
    fi
fi
done

printf 'Elapsed time: %s\n' $(timer $T)