new script: image compress

README.md

@@ -41,6 +41,11 @@ kill every wine process including processes hanging
 ### webptogif.sh 
 convert animated .webp at $1 (path) to a gif
 
+### image_compress.sh 
+Usage: `./image_compress.sh <input> <output.jpg> <size in bytes>`  
+Compress an image until it's below a specified target size. Output format is JPEG, regardless of the input format.  
+(requires ImageMagick)
+
 ### convert_md_to_pdf.sh
 (need to be used with listings-setup.tex in the same folder, xelatex and pandoc are required)   
 convert infile.md in the current folder to a pdf file (outfile.pdf) with code blocks in red boxes.

image_compress.sh

@@ -0,0 +1,68 @@
+#!/bin/bash
+
+input="$1"
+output="$2"
+target_size=$3
+
+if [[ -z "$input" || -z "$output" || -z "$target_size" ]]; then
+    echo "Usage: $0 input output.jpg <target size in bytes>"
+    exit 1
+fi
+
+compress_and_get_size() {
+    local q=$1
+    magick "$work" -strip -interlace Plane -quality "$q" "$output"
+    stat -c%s "$output"
+}
+
+
+work=$(mktemp --suffix=.jpg)
+cp "$input" "$work"
+
+magick "$input" \
+    -auto-orient \
+    -colorspace sRGB \
+    -strip \
+    -background white -alpha remove -alpha off \
+    "$work"
+
+echo "Trying to fit below $target_size bytes"
+
+while true; do
+
+    # Binary search
+    low=1
+    high=95
+    best_q=1
+
+    while (( low <= high )); do
+        mid=$(((low + high) / 2))
+        size=$(compress_and_get_size "$mid")
+
+        echo "    Quality $mid -> $size bytes"
+
+        best_size=$size
+
+        if (( size <= target_size )); then
+            best_q=$mid
+            low=$((mid + 1))
+        else
+            high=$((mid - 1))
+        fi
+    done
+
+    echo "Best quality this round: $best_q ($best_size bytes)"
+
+    if (( best_size <= target_size )); then
+        echo "DONE: $output is $best_size bytes"
+        break
+    fi
+
+    echo "  Reducing resolution"
+    tmp=$(mktemp --suffix=.jpg)
+
+    magick "$work" -resize 75% -quality 85 "$tmp"
+    mv "$tmp" "$work"
+done
+
+rm -f "$work"