Remove background from a PNG that already has transparency on Sume

Yes: run it through the cutout route anyway. In Sume's tool description for rmbg_create, the route is for any cutout request including when the source already has alpha, and it says not to skip. Inputs with substantial alpha are automatically flattened onto mid-gray #808080 before the background model sees them, and it is one bill. The output is a cutout PNG with alpha.

What Sume's description says

From the Sume MCP tool description for rmbg_create, which maps to POST /v1/rmbg-1.0/remove, model id sume/rmbg-1.0.

Why flatten

A background model works on pixels it can see. A mostly transparent image can hide the subject edge, so the route puts it on a neutral gray first. That is why a gray fringe is worth checking on semi-transparent regions such as glass or soft shadows.

Send it

Submit the hosted PNG and read the job result.

import os, requests

r = requests.post(
    "https://api.sume.com/v1/rmbg-1.0/remove",
    headers={"Authorization": f"Bearer {os.environ['SUME_API_KEY']}"},
    timeout=60,
    json={"image_url": "https://example.com/already-transparent.png"},
)
print(r.status_code)
print(r.json())

Check the edges

Open the result on a dark and a light background. If you see gray halos, the source probably had soft alpha near the edge; clean that mask in the source and run again.