Telegram sticker size 512: transparent PNG from an image API

A Telegram static sticker needs one side to be exactly 512 pixels and the other 512 or less, as PNG or WEBP. 512x512 is below GPT Image 2.5's 655,360-pixel floor, so request 1024x1024 with background: "transparent" and output_format: "png" on Sume, then scale it to 512x512 yourself.

Telegram's rules are from its stickers page; Sume's from the Image API docs. Both read 2026-10-01.

What does Telegram require?

Static stickers: one side exactly 512 px, the other no more than 512, in PNG or WEBP. Telegram says transparency is optional but recommended so the sticker stands out in chats.

Why not request 512x512?

Sume's docs give GPT custom sizes a minimum of 655,360 pixels; 512x512 is 262,144. 1024x1024 is 1,048,576 pixels with both edges multiples of 16, and halves cleanly to 512 (our arithmetic).

How do I get a transparent PNG?

background accepts auto, transparent or opaque on GPT Image 2.5. Keep a plain subject so cut edges stay clean.

curl -X POST https://api.sume.com/v1/images \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "openai/gpt-image-2.5",
    "prompt": "Sticker of a sleepy cartoon cat holding a coffee cup, thick white outline, no background",
    "image_size": "1024x1024",
    "background": "transparent",
    "output_format": "png"
  }'

What if my image already has a background?

Sume's RMBG 1.0 tool takes a public HTTPS image_url and returns a PNG with alpha, at $0.0225 per image. Run it, then resize to 512.

What are the numbers at a glance?

Pixel facts from the sections above.