320x50 and 468x60 banners from one 8:1 image: keep 80% and 97.5%

A 320x50 mobile strip is 6.4:1 and a 468x60 banner is 7.8:1, both narrower than the 8:1 that Nano Banana 2.1 lists on Sume. One 8:1 image at 1K costs $0.10, and cropping keeps 80% of the width for 320x50 and 97.5% for 468x60.

Crop math

At the same height, the width you keep is the slot ratio divided by 8.

Cost of the pair

Two sizes from one call cost $0.10 at 1K or $0.15 at 2K. Two separate calls would cost $0.20 or $0.30, and the two creatives would not match each other.

import os, requests

body = {
    "model": "google/nano-banana-2.1",
    "prompt": "Wide web banner, product left of centre, solid soft background, headline space on the right",
    "aspect_ratio": "8:1",
    "resolution": "1K",
}
r = requests.post(
    "https://api.sume.com/v1/images",
    headers={"Authorization": f"Bearer {os.environ['SUME_API_KEY']}"},
    json=body, timeout=60,
)
print(r.status_code)  # 200 = image body, 202 = job envelope
if r.status_code == 200:
    out = r.json()
    print(out["data"][0]["url"], out["usage"]["cost"])

Gotchas

• Keep logo and call to action inside the centre 75% of the width, so the 320x50 crop cannot cut them.
• Trim evenly from both sides unless the layout puts the subject on one side.
• GPT Image 2.5 stops at 3:1, so it cannot make this shape in one pass; Nano Banana 2.1 is the row that lists 8:1.
• Resize the crop to the final pixel size with your own tool; Sume's size field is a resolution shorthand, not pixels.