Pad an AI image to a white square for listings with ImageOps.pad

Call ImageOps.pad(img, (1600, 1600), color="white"). It scales the image to fit inside the square, keeps its ratio, and fills the leftover bands with white, so nothing is cropped. A 4:5 image at 1600 pixels square becomes 1280 by 1600 with a 160 pixel white band on the left and the right.

Crop versus pad

A square listing slot forces a choice. Cropping with ImageOps.fit keeps the picture full but removes edges, which can cut a handle, a sleeve, or a shadow. Padding keeps every pixel and adds blank space.

For marketplace and catalog images, padding on white is the safer default, since the product is the point and a cut-off product is a rejection reason. For social feeds, a crop usually looks better.

The call

pad takes the image, a target size, a resampling method, a color, and a centering pair. Centering (0.5, 0.5) puts the image in the middle. A value of (0.5, 1.0) sits the product on the bottom edge, which can suit items on a floor.

import os, io, requests
from PIL import Image
H = {"Authorization": "Bearer " + os.environ["SUME_API_KEY"]}
def gen(**body):
    r = requests.post("https://api.sume.com/v1/images", json=body, headers=H, timeout=60)
    r.raise_for_status()
    if r.status_code == 202:
        raise SystemExit("queued, read /v1/jobs/{id}/result: " + r.text)
    return r.json()
def fetch(u):
    return Image.open(io.BytesIO(requests.get(u, timeout=60).content))
from PIL import ImageOps
out = gen(model="google/nano-banana-2", aspect_ratio="4:5",
          prompt="Brown leather backpack on a pure white seamless backdrop, product photo")
img = fetch(out["data"][0]["url"]).convert("RGB")
square = ImageOps.pad(img, (1600, 1600), Image.LANCZOS, color="white", centering=(0.5, 0.5))
square.save("listing_square.jpg", quality=92)
w = round(1600 * img.width / img.height) if img.height >= img.width else 1600
print(img.size, "->", square.size, "image width inside", w, "cost", out["usage"]["cost"])

Band size by source ratio

The bands follow from the ratio. At 1600 pixels square, these are the white areas you add.

Make the white match

• Ask the model for a pure white backdrop. A cream or gray backdrop next to pure white bands shows as a visible box.
• Check the corner pixel of the image. If it is not 255 on each channel, either prompt again or flood the backdrop to white first.
• Keep the original aspect for web pages and use the square only where the form demands it.
• Use Image.LANCZOS when shrinking and save quality 90 or more.

Related

For a feed crop instead of a pad, see the 4:5 feed image recipe. Derive other widths from one master with the srcset recipe, and keep a lossless master as in PNG between passes. Check each marketplace's current size and background rules before you set the target.