Ideogram 4.5 size source: keep dimensions, and Sume aspect auto

Ideogram 4.5's size accepts "auto", "source" or an exact WIDTHxHEIGHT; source is rejected when you send no source images. Sume has no source value: its size is only a shorthand for a resolution tier, explicit pixels are not served in v1, and the way to match a reference is aspect_ratio: "auto".

Ideogram facts are from its Ideogram 4.5 reference; Sume facts from the Image API, read 2026-10-01.

What does each Ideogram 4.5 size value do?

Without source images, an exact size must be one of the supported 1K or 2K presets (the page gives 1024x1024, 2048x2048 and 1440x2880 as examples), auto or an omitted field picks a supported size from the prompt, and source is rejected. With source images, auto is the default and picks a supported 2K size from the sources and the prompt. The snapshot text for the rest of that sentence is cut off, so read the page for what source returns.

What does size mean on Sume?

The request table says size is a shorthand for a resolution tier and that explicit pixels are not served in v1. The docs add: do not put custom pixels on size; use image_size or aspect_ratio. seed, output_compression and explicit pixel size are advertised by no model, so they return 400 unsupported_parameter. Tiers are 512, 1K, 2K and 4K.

How do I keep a reference's shape on Sume?

On edit and image-to-image calls, send aspect_ratio: "auto" to match the reference; the docs say omitting the field is not the same as auto. Combine it with a resolution tier your model lists. That gives you the shape of the input, though not a promise of the same pixel count: Sume's tiers are normalized, and exact pixels are a separate step.

If you need exact output pixels, resize afterward. See image API aspect ratios and custom sizes for what each ratio and tier gives.

Which one should I send?

On Ideogram: auto is the default with source images; the snapshot cuts off before saying what source returns, so read the page before relying on it. On Sume: aspect_ratio: "auto" for edits, or a named ratio for a fixed shape, and never a WIDTHxHEIGHT string in size. Read the model's supported_parameters before sending either.