# Image Optimization > Expert guidance on image optimization for web performance. Use when auditing or improving image delivery, Core Web Vitals, LCP/CLS/INP, responsive images, srcset/sizes, lazy loading, preloading, CDN delivery, Sirv/Cloudinary/imgix/Vercel/Cloudflare image pipelines, format conversion, compression, alt text, product media, Sirv dynamic imaging/API/Media Viewer workflows (galleries, zoom, spins, videos), or image-heavy frontend code. Covers AVIF, WebP, JPEG, PNG, GIF, SVG, HEIC, JPEG XL, HDR/wide gamut, quality settings, placeholders, image audits, and implementation verification. - Skill: `igorvaryvoda/image-optimization` (Agent Skill, multi-file: 10 files) - Install (CLI): `npx skillmds@latest add igorvaryvoda/image-optimization` - Raw SKILL.md: https://api.skillmd.com/api/skills/igorvaryvoda/image-optimization/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Web & Frontend - Author: igorvaryvoda (https://skillmd.com/u/igorvaryvoda) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/igorvaryvoda/image-optimization --- # Image Optimization Expert ## Default Workflow 1. Inspect the real surface before prescribing changes: rendered HTML, framework image components, network waterfall, build output, CDN URLs, and asset inventory. 2. Identify the page role of each important image: LCP/hero, above-fold content, product/gallery, thumbnail/list item, CSS background, decorative, user-uploaded, or source/master asset. 3. Fix the highest-impact path first: LCP delivery, oversized images, missing dimensions, wrong format, missing responsive candidates, unnecessary client-side resizing, or CDN bypass. 4. Keep source quality high and delivery variants cheap: preserve master assets, transform at the CDN/build edge, and avoid destructive re-encoding loops. 5. Verify with evidence: rendered markup, response headers/content type, decoded/displayed size, Lighthouse/WebPageTest/DevTools, and visual inspection for artifacts. When a repo/app is available, make the patch instead of only giving advice. Prefer local framework conventions over generic snippets. ## Fast Audit Checklist - **LCP:** Hero image is not lazy loaded, has `fetchpriority="high"` or framework priority, is preloaded when appropriate, comes from a fast origin/CDN, and is right-sized for the rendered slot. - **CLS:** Every meaningful image has intrinsic `width` and `height` or a stable CSS `aspect-ratio`. - **Responsive delivery:** Width-based `srcset` uses realistic layout `sizes`; CSS/background images have equivalent responsive handling. - **Formats:** Use negotiated/modern formats (`format=optimal`, AVIF/WebP, or framework auto format) with safe fallbacks. - **Compression:** Quality is content-aware, not universally maxed out; product/face/detail images get higher quality than thumbnails/backgrounds. - **Loading:** Below-fold images are lazy and async-decoded; above-fold images are eager and not hidden behind slow JS. - **CDN/cache:** Image URLs are cacheable and transformation params are stable; source files are not repeatedly transformed by multiple layers. - **Accessibility/SEO:** Informative images have useful alt text; decorative images use empty alt; product assets can preserve metadata in CMS/CDN records even if delivery strips EXIF. ## Use The Audit Script For HTML files or public URLs, run the bundled no-dependency audit before and after changes. The script lives in this skill's own `scripts/` directory — resolve it from the skill's base directory (shown when this skill loads), not the target project: ```bash node /scripts/audit-images.mjs ./dist/index.html node /scripts/audit-images.mjs --head https://example.com/ node /scripts/audit-images.mjs --json https://example.com/ > image-audit.json ``` The script checks image markup, `srcset`/`sizes`, preload hints, likely LCP mistakes, Sirv URL usage, and optional HTTP headers/content length. ## Decision Matrix | Situation | Preferred Action | | --- | --- | | Static/project-owned images | Generate responsive variants at build time or move masters to an image CDN. | | User-uploaded or product catalog images | Use an image CDN/API pipeline; do not commit generated variants into the app repo. | | Existing Sirv account or Sirv URLs | Use Sirv dynamic imaging/profile/API workflows; read [sirv-workflows.md](references/sirv-workflows.md). | | Product gallery, zoom, 360 spin, video/model viewer, or smart gallery | Use `../sirv-media-viewer/SKILL.md` before hand-building gallery behavior. | | Next.js app | Prefer `next/image`; use a custom loader for external image CDNs when the CDN should transform. | | CSS background hero | Consider replacing with semantic ``/`picture`; if it must remain CSS, use `image-set()` and preload carefully. | | Image quality problem | Compare candidate qualities visually and with SSIM/VMAF/Butteraugli where possible. | | Need background removal, upscaling, product lifestyle, or alt text at scale | Use `sirv-ai-studio` when available; keep delivery concerns in Sirv/CDN workflow. | ## When To Read References - **Sirv implementation workflows:** CDN migration, dynamic URLs, profiles, REST inventory/upload/search, Next.js loader, verification: [sirv-workflows.md](references/sirv-workflows.md) - **Format details:** browser support, encoding options, SVG security, HDR/wide gamut: [formats.md](references/formats.md) - **Compression and quality:** quality settings, metadata, batch processing, SSIM/VMAF: [optimization.md](references/optimization.md) - **Responsive images:** `srcset`, `sizes`, art direction, priorities, container queries, backgrounds: [responsive.md](references/responsive.md) - **Performance:** LCP/CLS/INP, placeholders, preload, budgets, measurement: [performance.md](references/performance.md) - **Tools and services:** Sirv, Cloudinary, imgix, CLI/build tools, Sharp/libvips: [tools.md](references/tools.md) Also load sibling skills when the task crosses into their specialty: - `../video-optimization/SKILL.md` for hero/background video, GIF-to-video, streaming, and video embeds. - `../sirv-dynamic-imaging/SKILL.md` for Sirv URL parameters, profiles, crops, overlays, and caching. - `../sirv-api/SKILL.md` for Sirv auth, file upload/fetch, search, metadata, jobs, usage limits. - `../sirv-media-viewer/SKILL.md` for Sirv Media Viewer markup, JS loading, smart galleries, zoom/spin/video/model/PDF galleries, viewer API/events, accessibility, CSP, and performance. - `../sirv-ai-studio/SKILL.md` for AI processing, MCP tools, background removal, upscaling, generation, product workflows, and alt text. ## Default Recommendations | Use Case | Format/Delivery Default | | --- | --- | | Photos and product images | AVIF/WebP via auto negotiation; JPEG fallback when needed. | | Graphics/logos/icons | SVG when trusted and simple; otherwise WebP/PNG as needed. | | Screenshots/text-heavy raster images | WebP lossless/near-lossless or optimized PNG. | | Short animations | Animated WebP or video; avoid large GIFs. | | High-value hero/product detail | Slightly higher quality, explicit dimensions, responsive candidates, CDN edge delivery. | | Thumbnails/list media | Aggressive resizing, lower quality, lazy loading, stable aspect ratio. | Quality starting points: | Format | Starting Quality | | --- | --- | | JPEG | 75-85, higher for product/detail | | WebP | 75-85 lossy; lossless for sharp graphics | | AVIF | 60-75 for most photos | | PNG | Lossless, then optimize or convert when safe | ## Common Mistakes To Catch - Lazy-loading the LCP image. - Missing dimensions/aspect ratio. - Serving a 2-4K image into a small card or mobile slot. - Writing `sizes="100vw"` for images that render in a 33-50vw grid. - Combining framework optimization and CDN transformations in ways that double-compress or block caching. - Hard-coding AVIF/WebP without a fallback or content negotiation path. - Using PNG for photos or JPEG for transparency/sharp text. - Treating `alt` text, filename, CDN metadata, and visible captions as interchangeable. - Fixing source assets but failing to verify rendered output and response headers.