Ideogram 4.5 21:9 returns 400 on Sume: use 2:1 at 2K and crop

Sending aspect_ratio: "21:9" to ideogram/ideogram-v4.5 on Sume returns a 400 that lists the supported ratios. The wide ratios it does support are 2:1 and 3:1, so for a 2560x1080 banner ask for 2:1 at 2K (2880x1440) and crop 225 px off the height.

Supported ratios

The Ideogram 4.5 catalog on Sume is the same 15-ratio set as Ideogram V3. Any colon ratio outside it, such as 21:9 or 4:1, is refused. Pixel strings are different: they are snapped to the nearest native ratio, and 2560x1080 snaps to 2:1.

The crop

2:1 is the closest wide ratio to 2.37 (2560 by 1080). At 2K that is 2880x1440, and the target ratio at that width is 1215 px tall, so 225 px of height goes, which is about 16 percent. Put your subject in the middle band and ask for empty space at the top and bottom.

This applies to text-to-image. A 1K edit with a 2:1 request is 1408x704 instead, so use resolution: 2K plus aspect_ratio: 2:1 if you need pixel room.

from PIL import Image, ImageOps

im = Image.open("banner-2880x1440.png").convert("RGB")
print("returned", im.size)
out = ImageOps.fit(im, (2560, 1080), Image.Resampling.LANCZOS)
out.save("banner-2560x1080.jpg", quality=90)
print("saved", out.size)

Check before you build on it

Run GET /v1/images/models and read the ratio list for the model before you hard-code it, because catalogs change. The Image API docs explain the endpoint. If a true 21:9 is a hard requirement, pick a model whose list contains it instead of cropping.

When not to do this

Do not crop text the model rendered into the picture. A 16 percent height loss is fine for a landscape, but it can cut a headline in half. Leave the text for a later composite step, or design the banner with the headline in the middle band.

Prompting for a crop

Tell the model what the crop will remove: "Keep the top and bottom 15 percent as empty sky or floor." Models do not know where you will cut, so say it. Put the subject in the middle band and any text there as well.

Check the crop on the actual banner. At 2560 wide a headline set by the model may land inside the cut, and moving it by prompt is a new paid try. Setting the text in code after the crop avoids that cost completely.