4:5 on FLUX.2 pro and Qwen Image becomes 1229x1536 on Sume

When you send aspect_ratio: "4:5" to FLUX.2 pro, Qwen Image or Recraft V4 on Sume, the request ends up as a 1229 x 1536 image. Sume's code turns a custom colon ratio into pixels with the longer edge set to 1536 and the shorter edge scaled to match, so 4:5 gives 1229 x 1536 (1536 x 4 / 5 is 1228.8, rounded up). It is not 1080 x 1350, which is what Instagram's 4:5 portrait is.

This is worth knowing before you plan an Instagram or Shopify asset, because the resolution you get is set by the ratio rather than by a size you chose, and every custom ratio on these models lands above one megapixel.

What the sources say

Sume's Image API docs list aspect_ratio values such as 4:5, 5:4, 3:2, 2:3, 21:9, 9:21, 1:2 and 2:1 for these models, and say that a model only accepts the values its catalog descriptors list. In the code, the five ratios that match fal's named presets (1:1, 16:9, 9:16, 4:3 and 3:4) go through as those presets, and every other listed ratio is converted to explicit pixels with a 1536 long side.

On the vendor side, the fal page for FLUX.2 [pro] offers 1K, 2K and 2.3K size presets with an aspect-ratio lock, and prices output at $0.03 for the first megapixel plus $0.015 per extra megapixel of input and output.

What that means for price

Each size in the table is over one megapixel, so on the vendor's pricing sentence each one counts as one first megapixel plus a fraction of an extra one. The page's own example of 1920 x 1080, about 2.07 megapixels, is $0.045 against $0.03 for 1024 x 1024. I do not derive an exact figure for 1229 x 1536 because the page does not say how it rounds a partial megapixel.

For what Sume charges, read the endpoint record for the id you use, or run a small batch and read usage.cost on the response. The docs state that cost is the USD amount billed to your wallet.

Getting a true 1080 x 1350

If the destination needs 1080 x 1350, treat the Sume image as a source: the ratio is 0.80013, a hair off 0.8, so a one-pixel crop and a resize get you there. The Image API docs say the same for Nano Banana Pro, where exact 1080 x 1350 is a post-step. The Pillow snippet below crops to exactly 4:5 and resizes with Lanczos filtering.

If you need exact pixels for a marketplace, generate at the 4:5 ratio and resize, instead of asking for a custom size that the model's rules do not allow.

One more check applies to the 21:9 and 9:21 rows: at 658 pixels on the short edge they are the smallest of the set, so a banner made from them is a draft size. If the final needs more width, generate at the nearest listed ratio and upscale or extend it in a second step instead of asking for a bigger canvas.

from PIL import Image

img = Image.open("flux-4x5.png")  # 1229 x 1536 from Sume
w, h = img.size
target_w = round(h * 4 / 5)  # 1229
left = (w - target_w) // 2
img = img.crop((left, 0, left + target_w, h))
img.resize((1080, 1350), Image.LANCZOS).save("feed-1080x1350.png")
print(img.size)