AI AI Tools Guidebook
Troubleshooting

AI Image Wrong Aspect Ratio

You set 9:16, output came 1:1. Tool-specific param syntax, model support, and override defaults — each platform handles aspect differently.

Published: Author: AI Productivity Guide Team 🌐 查看中文版本

You needed a 9:16 vertical for Instagram Reels and got back a 1:1 square. Or you set —ar 21:9 cinematic and got 16:9. The image content is fine — the aspect is just wrong.

This is almost always a UI / parameter issue, not a model issue. Each platform parses aspect differently, and some models don’t support extreme ratios at all.

Common causes

Ordered by hit rate, highest first.

1. Aspect parameter written in unsupported syntax

--ar 9:16 works on Midjourney but not on most SDXL UIs. Writing it as a Midjourney flag inside an SDXL prompt gets ignored.

How to spot it: aspect string is --ar X:Y and you’re not on Midjourney. The flag is being eaten as text.

2. Model has a forced output resolution

Some hosted models (older DALL-E versions, some image API endpoints) only output square — --ar is silently ignored.

How to spot it: check the model’s docs / pricing page for supported resolutions. If it lists only “1024×1024,” that’s all you get.

3. UI default overrides prompt

You set --ar 16:9 in the prompt, but the UI’s resolution dropdown is on “1024×1024 square” and overrides. Common in ComfyUI, A1111, and some web UIs.

How to spot it: change the UI’s dropdown to match the desired aspect. Prompt aspect flag is often ignored when UI explicitly sets resolution.

4. Extreme ratio not supported

32:9, 1:5, 21:9, even 9:16 are unsupported on some checkpoints. Model returns the nearest supported.

How to spot it: same prompt at 9:16 returns 1:1, but at 2:3 works fine. Model has a constrained set.

5. Aspect set in pixels rather than ratio

You set 768×1344 thinking it’s 9:16. Check the math: 768/1344 = 0.571 ≈ 4:7, not 9:16. Off-by-pixel errors are common.

How to spot it: divide width by height; compare to your target ratio. If off, recalculate.

6. Output saved/exported in different aspect

The model generated correctly, but the platform’s auto-export rendered to a different aspect (square Instagram preview, etc.).

How to spot it: download the raw original PNG. Compare dimensions to what’s displayed.

Shortest path to fix

Step 1: Use the right syntax per platform

# Midjourney
"... --ar 9:16"
"... --ar 16:9"
"... --ar 1:1"  (default)
"... --ar 21:9"
"... --ar 3:2"

# SDXL via A1111 / Forge
- Set Width × Height in the UI directly
- Common ratios:
  - 1:1   → 1024×1024
  - 9:16  → 768×1344
  - 16:9  → 1344×768
  - 4:5   → 896×1152
  - 21:9  → 1536×640

# ComfyUI
- EmptyLatentImage node — set width and height
- Use ratios divisible by 64 for SDXL

# DALL-E 3 (ChatGPT)
- Ask "make this 9:16 vertical" in the message
- Supported: 1024×1024, 1024×1792 (portrait), 1792×1024 (landscape)
- No --ar flag

# Flux dev (ComfyUI)
- Width × Height (divisible by 16)
- Supported up to ~2048 on a side

Step 2: Generate at supported ratio, then crop

For unsupported ratios (32:9, 5:1, very tall):

1. Generate at nearest supported (16:9, 21:9, or 9:16)
2. Open in Photoshop / Pixelmator / Photopea
3. Crop to target aspect
4. Upscale back to target dimensions if needed

Add 10% padding to the prompt’s subject framing so cropping doesn’t cut into it.

Step 3: Check model’s supported aspect list

Per platform docs:

Midjourney v6: 1:1, 9:16 to 16:9, plus --ar up to 21:9 typically supported
SDXL: any ratio with both dims divisible by 64, total pixels ~1M
Flux: any ratio with both dims divisible by 16
DALL-E 3: only 1:1, 7:4 (1792×1024), 4:7 (1024×1792)
Stable Diffusion 3: same as SDXL roughly
Imagen 3: 1:1, 9:16, 16:9, 3:4, 4:3

Step 4: Override UI defaults

In ComfyUI / A1111 / Forge:

- Check the UI's Width / Height fields
- Make sure they match what you wrote in the prompt
- If they conflict, UI fields usually win
- For A1111: also check "Hires fix" target resolution

Step 5: Sanity-check pixel math

# Quick aspect check
def aspect(w, h):
    from math import gcd
    g = gcd(w, h)
    return f"{w//g}:{h//g}"

# Examples
aspect(1024, 1792)  # → "4:7" (not 9:16, which would be 576:1024 = 1008 px close to "9:16")
aspect(768, 1344)   # → "4:7" (also not 9:16, which exactly = 576:1024 or 1080:1920)

For exact 9:16, use 1080 × 1920 or 576 × 1024 or 768 × 1365 (slight rounding).

Step 6: Confirm exported file aspect

Download the raw PNG. Check file dimensions in Finder / Explorer / identify image.png. Compare to expected. If different, the export pipeline is altering aspect — bypass it.

Prevention

  • Save a per-platform aspect cheatsheet (Midjourney --ar syntax, SDXL pixel dims, DALL-E supported set)
  • For series work, always generate at the same aspect; never mix
  • Default to slightly bigger + crop, not “extreme ratio + hope”
  • Test pixel dimensions against intended ratio (math the math, don’t eyeball)

Tags: #Image generation #Debug #Troubleshooting

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