n8n Workflow: Auto Generate Branded Social Images from Google Sheets

Auto-generate branded social image PNGs from your Google Sheets topics—powered by n8n + OpenAI + Polotno

This n8n workflow reads unprocessed topics from a Google Sheets content calendar, generates a headline and subheadline with OpenAI, renders a branded PNG using the Polotno Images API, and writes the resulting image URL back to the same row—automatically (daily at 8am) or on demand.

What this workflow does

• Triggers manually or on a schedule: runs on demand or every morning at 8am.
• Pulls only the right rows: reads your Google Sheets rows and keeps items where Topic is filled and Generated Image is empty.
• Generates copy with OpenAI: sends each Topic to OpenAI and expects a strict JSON response containing a headline and subheadline.
• Renders a branded PNG via Polotno: calls the Polotno Images API to render a PNG from your template, injecting the generated copy (and an optional source image URL as a dynamic field).
• Verifies render success: checks that the Polotno render completed successfully.
• Writes results back to Google Sheets: updates the originating row with the returned image URL, or records the failed row number and error message for troubleshooting.

Use cases

• Populate a weekly content calendar with topics and automatically produce branded social assets.
• Batch-generate images for SaaS marketing posts without manual copywriting or design work.
• Use a consistent Polotno template to keep brand styling uniform across all generated graphics.

Technical details

• Google Sheets integration: reads from a specified spreadsheet/sheet and updates rows (requires columns like Topic, Image URL, and Generated Image, plus row number for updates).
• OpenAI integration: generates headline + subheadline from each topic (e.g., model such as gpt-4o-mini).
• Polotno Images API: renders a branded PNG from a Polotno Studio template ID using HTTP Request with Authorization: Bearer <your_polotno_key>.
• Workflow logic / nodes: uses if, set, code, filter, sticky note, and http request.