Script to resize large thumbnails before upload into DSpace

resize-thumbnails.sh

#!/usr/bin/env bash
#
# Check pre-generated thumbnails to see if their dimensions are appropriate for
# uploading to DSpace. Some thumbnails come from Flickr or YouTube and are very
# high definition (2000px!), so we resize them to something more appropriate.
#
# Expects to be run while inside a directory of JPEGs. Haven't tested with PNGs.
# 
# Alan Orth, 2016-05

# Exit on first error
set -o errexit

readonly IM_CONVERT_BIN=/usr/bin/convert
readonly IM_IDENTIFY_BIN=/usr/bin/identify
readonly THUMBNAIL_MAX_HEIGHT=400
readonly THUMBNAIL_MAX_QUALITY=82
readonly OUTPUT_DIR=processed_thumbnails

main() {
    local thumbnail
    local thumbnail_height
    local thumbnail_quality

    mkdir -p $OUTPUT_DIR

    for thumbnail in *.jpg
    do
        echo "Processing $thumbnail"

        # get thumbnail's height
        thumbnail_height=$($IM_IDENTIFY_BIN -format %H $thumbnail)

        # see if its height is larger than we want
        if [[ $thumbnail_height -gt $THUMBNAIL_MAX_HEIGHT ]]; then
            echo "> Height is too large ($thumbnail_height), resizing"

            # check image quality (JPEG specific?)
            thumbnail_quality=$($IM_IDENTIFY_BIN -format %H $thumbnail) 

            # see if its quality is higher than we want
            if [[ $thumbnail_quality -gt $THUMBNAIL_MAX_QUALITY ]]; then
                echo ">> Quality is too high, will use $THUMBNAIL_MAX_QUALITY"
                $IM_CONVERT_BIN "$thumbnail" -resize x${THUMBNAIL_MAX_HEIGHT} -quality $THUMBNAIL_MAX_QUALITY -strip $OUTPUT_DIR/$thumbnail
            else
                # otherwise ImageMagick uses the image's existing quality setting
                $IM_CONVERT_BIN "$thumbnail" -resize x${THUMBNAIL_MAX_HEIGHT} -strip $OUTPUT_DIR/$thumbnail
            fi
        else
            echo '> Height is fine, copying to output directory'

            # just copy the existing thumbnail to the output directory
            cp $thumbnail $OUTPUT_DIR
        fi
    done
}

main

# vim: set expandtab:ts=4:sw=4:bs=2