remove.bg bg_color replacement: Sume RMBG gives a transparent PNG

Sume RMBG 1.0 has no bg_color or bg_image_url. Its request takes an image_url and the completed result is a PNG with alpha, so a background color or scene is something you add in a second step.

remove.bg's changelog lists bg_color (added 2019-04-15) and bg_image_url (added 2019-06-03). Sume's side is from the API reference and image docs, read 2026-10-01.

What does the Sume removal request accept?

The schema is described as "Sume RMBG 1.0 background-removal request. Provide a public HTTPS image_url." The required field list is image_url and nothing else; the other fields are sync_mode, metadata, and delivery fields such as mode. Unknown fields are not accepted by the schema.

How do I get a colored or scene background?

Two documented paths. For a flat color, composite the transparent PNG over that color in your own code or editor. For a generated scene, pass the cutout's public HTTPS URL in input_references of an image request and describe the new background in the prompt; the field is described as "Reference images for image-to-image". White background to lifestyle scene walks through that second step.

Does the input need to be opaque?

No special handling is required, but the OpenAPI description notes that when the input already has substantial fully transparent pixels, Sume flattens it onto mid-gray #808080 before provider submission so edges stay clean, still as one billed removal.

What should I do first?

Find where your code sets bg_color. If it is a plain color, move that into a compositing step after download. If it is an image, plan the second request.