AgentSkillsCN

compress-images

使用 cwebp 压缩图片，以提升网页性能和搜索引擎优化效果。在优化图片以实现更快的页面加载速度、减小文件大小，或将 JPG/PNG 转换为 WebP 格式时，可优先选用此工具。

SKILL.md
--- frontmatter
name: compress-images
description: Compress images for web/SEO performance using cwebp. Use when optimizing images for faster page loads, reducing file sizes, or converting JPG/PNG to WebP format.
argument-hint: "[directory]"
allowed-tools: Bash(cwebp:*), Bash(ls:*), Bash(mkdir:*), Bash(mv:*)

Image Compression Skill

Compress all images in $ARGUMENTS (or app/assets/images/content/ if no path provided) to WebP format, optimized for SEO performance (target: under 100KB per image).

Process

  1. •Create originals folder - Create originals/ subfolder inside the target directory and move source files there. Never destroy source files.
  2. •Compress each image (JPG, PNG, GIF) from originals/ to the parent directory as .webp
  3. •Iterate until all images are under 100KB - check sizes after each pass, re-compress any that exceed the target
  4. •Report results with before/after sizes
  5. •Update references in content files from old extensions to .webp

File Structure

code
target-directory/
├── originals/           # High-quality source files preserved here
│   ├── hero.jpg
│   └── feature.png
├── hero.webp            # Compressed, web-optimized
└── feature.webp

Iterative Compression Algorithm

IMPORTANT: Keep compressing until ALL images are under 100KB. Check sizes after each pass and re-compress any that exceed the target.

Step 1: Initial pass (q 70)

bash
cwebp -q 70 -resize 1200 0 originals/image.jpg -o image.webp
ls -lh image.webp  # Check size

Step 2: If still over 100KB, reduce quality progressively

bash
# Try these in order until under 100KB:
cwebp -q 60 -resize 1200 0 originals/image.jpg -o image.webp
cwebp -q 50 -resize 1200 0 originals/image.jpg -o image.webp
cwebp -q 45 -resize 1200 0 originals/image.jpg -o image.webp
cwebp -q 40 -resize 1200 0 originals/image.jpg -o image.webp
cwebp -q 35 -resize 1200 0 originals/image.jpg -o image.webp

Step 3: For stubborn images, also reduce dimensions

bash
# If q 35 at 1200px is still over 100KB, reduce to 1000px:
cwebp -q 30 -resize 1000 0 originals/image.jpg -o image.webp
cwebp -q 25 -resize 1000 0 originals/image.jpg -o image.webp

Real-World Results (Reference)

From actual compression run on content images:

ImageOriginalFirst TryFinalSettings Used
waves.jpg198KB33KB33KBq 70, 1200px (1 pass)
calendar.jpg246KB42KB42KBq 70, 1200px (1 pass)
floating.jpg230KB43KB43KBq 70, 1200px (1 pass)
cash.jpg409KB88KB88KBq 70, 1200px (1 pass)
knot.jpg395KB96KB96KBq 70, 1200px (1 pass)
floating-dark.jpg414KB94KB94KBq 70, 1200px (1 pass)
keyboard2.jpg459KB102KB102KBq 70, 1200px (1 pass, acceptable)
perpetual.jpg565KB130KB96KBq 40, 1200px (3 passes)
keyboard.jpg718KB196KB98KBq 25, 1000px (5 passes)

Key Insights

  1. •Most images (under 500KB source) compress fine with default settings (q 70, 1200px)
  2. •Large detailed images (500KB+) often need multiple passes
  3. •Very large images (700KB+) may need both lower quality AND smaller dimensions
  4. •Keyboard/tech photos with fine detail are hardest to compress - expect 4-5 passes
  5. •Soft/blurry images compress much better than sharp detailed ones

After Compression

  1. •Verify ALL files under 100KB: ls -lh *.webp - re-run compression on any exceeding target
  2. •Update content files referencing old extensions (.jpg, .png) to use .webp
  3. •Test that images render correctly in the application
  4. •Original files remain in originals/ folder for future reference or re-compression