Compress Png

Compress PNG

Overview

Audit large PNGs and compress them with a reusable script instead of re-deriving one-off shell commands. Prefer this skill for report figures, experiment result folders, and screenshot-heavy assets where PNG is still the right format but the files are too large.

Workflow

1. Audit the target folder before editing anything. Use --audit-only and a size threshold so you only touch the problem files.
2. Start with copy mode, not in-place replacement. The default script behavior writes sibling files with a suffix so you can compare quality first.
3. Use 256 colors first. This usually cuts screenshot-like or microscope-photo PNGs dramatically while keeping the image visually close.
4. Only get more aggressive if needed. Drop to 128 colors or set --max-dimension when the first pass is still too large.
5. Replace originals with --in-place only after checking a sample of the compressed outputs.

Quick Start

Audit the largest PNGs in a result folder:

python3 /root/.codex/skills/compress-png/scripts/compress_png.py \
  AI_works/results/晶体光学性质/picture-results \
  --audit-only \
  --min-size-mb 1 \
  --top 20

Write compressed copies next to originals:

python3 /root/.codex/skills/compress-png/scripts/compress_png.py \
  AI_works/results/晶体光学性质/picture-results \
  --min-size-mb 1 \
  --colors 256

Replace the original files after checking quality:

python3 /root/.codex/skills/compress-png/scripts/compress_png.py \
  AI_works/results/晶体光学性质/picture-results \
  --min-size-mb 1 \
  --colors 256 \
  --in-place

Use a more aggressive pass when huge camera PNGs still need work:

python3 /root/.codex/skills/compress-png/scripts/compress_png.py \
  AI_works/results/晶体光学性质/picture-results/conoscopic-mode \
  --min-size-mb 2 \
  --colors 128 \
  --max-dimension 2400

Script Notes

• The script prefers ImageMagick (magick or convert) because it is faster on very large images.
• The script falls back to Pillow if ImageMagick is unavailable.
• The script skips outputs that are not actually smaller unless --keep-larger is set.
• The default output is a sibling file named like image-compressed.png.
• Use --output-dir DIR when you want to keep the originals untouched and place all compressed outputs elsewhere.

Quality Guardrails

• Prefer 256 colors first for lab screenshots, optical patterns, and report figures.
• Lower to 128 colors only when the first pass is still too large or the image is mostly smooth gradients with repeated colors.
• Use --max-dimension for oversized camera images. It is often the biggest win when a figure was captured at full sensor resolution but only displayed at report scale.
• Visually inspect a few representative samples before using --in-place.
• Do not switch to JPEG unless the user explicitly asks; this skill is for keeping PNG output.

Files

• scripts/compress_png.py: audit and compress one file or whole directory trees