Image transformations let you show images in the size or format you need. Create a new version by calling variant on an attachment and passing the desired transformations. When a browser requests that URL, Active Storage will process the original image on demand and redirect to the generated file.

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Active Storage variants enable image transformations in Rails through a lazy processing system. When you call variant on an attachment, Rails returns a Variant object representing transformation intent without immediate processing. The actual transformation happens on first URL request: Rails downloads the original, applies transformations via Vips or ImageMagick, and uploads the result. Subsequent requests serve the cached variant from storage. The system uses signed URLs to prevent tampering, deterministic storage keys for caching, and optional database tracking via VariantRecord. You can preprocess variants to avoid first-request latency or use lazy loading for on-demand generation.

How Active Storage Variants Work to Transform Images in Rails

VariantWithRecord: Database-Backed Tracking

Preprocessed Variants: Avoiding Lazy Loading