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#!/bin/bash
# Converts input images to one-page PDF files each, without changing image data.
# The image is centered on a A4 page with a 5% border.
# Adapted from https://unix.stackexchange.com/a/220114
#
# Usage: [command] image1.jpg image2.png ...
# Output: PDF files named after the images e.g. image1.pdf
# Page dimensions (A4)
pageWidth=8.27
pageHeight=11.69
# bc function to calculate maximum of two floats
bc_functions="
define max(a,b) {
if (a>b) {
return(a)
} else {
return(b)
}
};";
# Do the calculation in string $1 and echo the result.
function calc {
# Define bc functions so we can use it for the calc.
echo "$bc_functions $1" | bc -l;
}
for file in "$@"; do \
# Determine image dimensions in pixels.
img_size_x=$(identify -format "%w" "$file");
img_size_y=$(identify -format "%h" "$file");
# Calculate image density (in dpi) needed to fit the image and a 5%
# border all around on an A4 page (8.27x11.69"). Factor 1.1 creates
# 2*5% borders, see https://unix.stackexchange.com/a/220114 for details.
min_density_x=$(calc "$img_size_x / $pageWidth * 1.1");
min_density_y=$(calc "$img_size_y / $pageHeight * 1.1");
# Use the higher density to prevent any dimension exceeding the required fit.
density=$(calc "max($min_density_x,$min_density_y)");
# Calculate canvas dimensions in pixels.
# (Canvas is an A4 page (8.27x11.69") with the calculated density.)
page_size_x=$(calc "$pageWidth * $density");
page_size_y=$(calc "$pageHeight * $density");
offset_x=$(calc "($page_size_x - $img_size_x) / 2 * 72 / $density");
offset_y=$(calc "($page_size_y - $img_size_y) / 2 * 72 / $density");
# Center image on a larger canvas.
# "${file/%.*/.pdf}" - changes extension to .pdf via parameter substitution.
convert "$file" \
-page ${page_size_x}x${page_size_y}+${offset_x}+${offset_y} \
-units PixelsPerInch -density $density \
-format pdf -compress jpeg \
"${file/%.*/.pdf}";
done;