Covers on Autopilot — Why I Let AI Paint the Edges

4 minute read Published: 2025-10-30
Covers on Autopilot — Why I Let AI Paint the Edges cover

There are jobs you can do by hand for years and never notice the drag. For me it was cover images. Each new post: open a design tool, stare at a blank canvas, export a PNG, wire it to the post. Not hard, just enough friction to make publishing feel heavier than it should.

This is a short note about shaving that yak with a tiny toolchain: a context‑aware prompt, an image model, and some guardrails in CI. No heroics—just removing a repeated decision so the writing flows.

Why automate covers

  • Consistency: 1200×630 every time. No more odd crops in link unfurls.
  • Momentum: publishing shouldn’t wait for “design time”.
  • Style: light background, a single accent, abstract shapes. Enough personality, zero fuss.

Over time the manual step was turning into a speed bump. That was the whole motivation.

The bumps along the road (the important part)

I didn’t get it right on the first try. Here are the lessons that actually mattered.

  1. Model and limits

At first I used Stable Horde for SDXL. It’s great and free, but CI doesn’t love queues. I kept seeing 400/429s in the logs (invalid payload or rate‑limited). Switched to Replicate with an API token; still got rate limits sometimes, but at least the errors were predictable.

  1. Exact sizing

SDXL likes multiples of 64. I request 1024×576, then downscale to 1200×630 with Sharp. Crisp edges, correct aspect for social cards.

  1. Slugs vs. filenames

My fallback logic assumed page.slug exactly matched the filename. It didn’t—some posts derive the slug from the permalink. I fixed the template to compute slug-from-permalink and look for /images/covers/{slug}.png. Simple, but that bug cost the most time.

  1. “Why is it regenerating?”

CI starts from a clean checkout. If covers aren’t in Git, they disappear each run. I added a cache step that restores static/images/covers keyed to content/posts/**/*.md. Now the generator truly skips when a PNG already exists.

  1. Context in prompts

Pure tags produced vague images. I added a little context: title + ~240 chars of summary (description if present, otherwise a clean slice of the body). Still abstract, just more grounded.

  1. One‑time resets

Sometimes you do want a full refresh. There’s a manual “Run workflow” input (force_regenerate=true) that bypasses the “file exists” check once. Good for style changes or a model upgrade.

How we decided on AI at all

I tried three options in order:

  • Hand‑made banners (historically): high quality, low velocity.
  • Programmatic shapes: reliable, but too repetitive.
  • AI with guardrails: abstract, brand‑aware, hands‑off once it’s set.

The third option hit the balance. The prompt constrains style; the model supplies variation. It’s not “art direction”, but it serves the post—and that’s the only job here.

The pipeline (nuts and bolts)

  • Script: scripts/generate-ai-covers.mjs

    • Scans content/posts/*.md, pulls tags, title, and a short summary.
    • Prompt (simplified):

      Abstract, minimal illustration. Tags: {tags}. Title: {title}. Context: {summary}. Vector‑like, clean geometric shapes, high contrast, brand accent #d64a48 on #f6f7f4. No text.

    • Calls Replicate SDXL (model version from a secret), requests 1024×576, saves 1200×630 as static/images/covers/{slug}.png.
    • Skips generation if the PNG already exists (unless FORCE_REGENERATE_COVERS=1).

  • Template: themes/radion/templates/page.html

    • If a post doesn’t specify a cover, it tries /images/covers/{slug-from-permalink}.png and hides the figure if missing.

  • CI: .github/workflows/deploy.yml

    • Restores a covers cache before generation; saves it after.
    • Optional manual input force_regenerate for a one‑time refresh.

What GitHub Actions brings

The boring kind of power: reliability.

  • Every run restores the previous covers, generates only what’s missing, and embeds without a front‑matter tweak.
  • When rate‑limited, the post still publishes—missing images pick up on the next run.
  • A small verification stage lists the covers in public/images/covers and checks that posts actually reference them.

Closing the loop

This wasn’t about making the site “AI‑powered”. It was about removing a tiny friction point that kept breaking the flow. The rule of thumb I keep coming back to: automate anything that steals attention from writing. Covers were stealing attention. Now they aren’t.

And if the art ever needs a new feel? I flip the model or tweak the prompt, hit “Run workflow”, and let the pipeline repaint the edges while I get back to words.