2nd/10_Wiki/Topics/AI_and_ML/Prompt Weight.md

---
id: wiki-2026-0508-prompt-weight
title: Prompt Weight
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [Prompt Weighting, Attention Weighting, Token Emphasis, Prompt Strength]
duplicate_of: none
source_trust_level: A
confidence_score: 0.9
verification_status: applied
tags: [prompt-engineering, generative-ai, stable-diffusion, midjourney, image-gen]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: Python
  framework: diffusers / ComfyUI / Automatic1111 / Midjourney
---

# Prompt Weight

## 매 한 줄
> **"매 emphasize / de-emphasize specific tokens in a prompt — `(word:1.3)` syntax of Stable Diffusion, `--w` of Midjourney, attention scaling under the hood"**. AUTOMATIC1111 (2022) 의 prompt-weight syntax 가 community standard 로 자리잡음. 2026 currently FLUX, SD3.5, SDXL Turbo, Midjourney v7 모두 weighting 지원; T5-encoded models 는 syntax 가 다름.

## 매 핵심

### 매 syntax (Stable Diffusion / A1111 / ComfyUI)
- `(word)` — weight ×1.1.
- `((word))` — ×1.21.
- `(word:1.3)` — explicit weight ×1.3.
- `[word]` — weight ÷1.1.
- `[word:0.5]` — weight ×0.5.
- `(red hair:1.4) (blue eyes:0.8)` — phrase-level.

### 매 syntax (Midjourney v7)
- `cat dog` — equal weight.
- `cat::2 dog::1` — double-colon multi-prompt with weights.
- `--w 0.5` — image weight (text vs reference image).
- `--s 250` — stylize strength.

### 매 syntax (FLUX / T5-encoded)
- T5 understands natural language; `(word:1.3)` syntax 매 mostly ignored.
- Use **emphasis via wording**: "very prominent X", "subtle hint of Y".
- Some forks (forge, ComfyUI) 매 still parse weights via re-prompting.

### 매 mechanism (under the hood)
- CLIP/T5 text encoder → token embeddings.
- A1111: weight w → multiply token embedding by w (post-encoding rescale).
- Compel library: more sophisticated — interpolates between conditioning vectors.
- Cross-attention scaling: alternative — scale K/V at attention layer.

### 매 best practices
- Stay between 0.5 and 1.5; 매 above 1.5 → distortion / saturation.
- Negative prompts often more effective than `[word]` syntax.
- Long prompts: weight the critical 3-5 tokens, leave rest at 1.0.
- For T5 models, use natural-language emphasis instead.

## 💻 패턴

### diffusers + Compel (programmatic weighting)
```python
from diffusers import StableDiffusionXLPipeline
from compel import Compel, ReturnedEmbeddingsType
import torch

pipe = StableDiffusionXLPipeline.from_pretrained(
    "stabilityai/stable-diffusion-xl-base-1.0", torch_dtype=torch.float16
).to("cuda")

compel = Compel(
    tokenizer=[pipe.tokenizer, pipe.tokenizer_2],
    text_encoder=[pipe.text_encoder, pipe.text_encoder_2],
    returned_embeddings_type=ReturnedEmbeddingsType.PENULTIMATE_HIDDEN_STATES_NON_NORMALIZED,
    requires_pooled=[False, True],
)

prompt = "a (red:1.4) sports car on a (sunny:0.7) beach, cinematic"
conditioning, pooled = compel(prompt)
image = pipe(prompt_embeds=conditioning, pooled_prompt_embeds=pooled).images[0]
```

### A1111-style parsing (manual)
```python
import re
def parse_weighted(prompt):
    """Return list of (text, weight) tuples."""
    out, depth_paren, depth_brack = [], 0, 0
    # Simplified: handles (text:1.3) only
    pattern = re.compile(r"\(([^():]+):([\d.]+)\)")
    parts, last = [], 0
    for m in pattern.finditer(prompt):
        if m.start() > last:
            parts.append((prompt[last:m.start()], 1.0))
        parts.append((m.group(1), float(m.group(2))))
        last = m.end()
    if last < len(prompt):
        parts.append((prompt[last:], 1.0))
    return parts
```

### Cross-attention scaling (Hugging Face)
```python
# Scale a specific token's attention by factor
from diffusers.models.attention_processor import AttnProcessor

class WeightedAttn(AttnProcessor):
    def __init__(self, token_idx, scale):
        self.token_idx, self.scale = token_idx, scale
    def __call__(self, attn, hidden, encoder_hidden, attention_mask=None):
        # In encoder_hidden, multiply token_idx slot by scale before attn
        encoder_hidden = encoder_hidden.clone()
        encoder_hidden[:, self.token_idx] *= self.scale
        return super().__call__(attn, hidden, encoder_hidden, attention_mask)
```

### Midjourney prompt
```
masterpiece anime girl::3 cyberpunk city background::1 neon lights::0.5
--ar 16:9 --s 500 --v 7
```

### FLUX-style natural-language emphasis (no syntax)
```python
# Bad (FLUX ignores):  "(red hair:1.5) girl"
# Good:                "girl with strikingly vivid red hair, the red is the most prominent color in the image"
```

### Prompt-blending (interpolate two prompts)
```python
from compel import Compel
c1 = compel("a cat in a forest")
c2 = compel("a robot in a city")
mixed = (c1 + c2) / 2  # Compel supports tensor arithmetic
image = pipe(prompt_embeds=mixed).images[0]
```

### Step-conditional weighting (`[from:to:step]`)
```
[cat:dog:0.5] in a field
# 0-50% steps: "cat", 50-100%: "dog"
# Useful for changing subject mid-denoising
```

## 매 결정 기준
| 상황 | Approach |
|---|---|
| SDXL / SD1.5 / SD2.1 | A1111 `(word:1.3)` syntax via Compel |
| FLUX / SD3.5 (T5) | Natural-language emphasis |
| Midjourney v7 | `::weight` syntax |
| Subject + style mix | Multi-prompt with `::` or compel blends |
| Subtle adjustment | 0.8-1.2 range |
| Strong push | 1.3-1.5; rarely above |
| Suppress concept | Negative prompt (preferred) over `[word]` |

**기본값**: Compel for SDXL programmatic; A1111 syntax for casual; natural language for FLUX.

## 🔗 Graph
- 부모: [[Prompt_Engineering|Prompt-Engineering]] · [[AI 이미지 생성 (AI Image Generation)|Image-Generation]]
- 변형: [[Negative Prompt]]
- 응용: [[Stable-Diffusion]] · [[FLUX]] · [[Midjourney]] · [[ComfyUI]]
- Adjacent: [[CLIP]] · [[Diffusion-Models]] · [[ControlNet]]

## 🤖 LLM 활용
**언제**: image generation pipelines, fine-grained subject/style control, automated prompt synthesis.
**언제 X**: text-only LLM prompts (GPT/Claude don't use this syntax — use emphasis words instead), T5-only models.

## ❌ 안티패턴
- **Weight > 2.0**: 매 saturated artifacts, deformed output.
- **Stacking parens** `(((((word)))))`: hard to read; use explicit `(word:1.6)`.
- **A1111 syntax on FLUX/T5**: silently ignored — switch to natural language.
- **Weighting every token**: dilutes effect; pick 2-4 priorities.
- **Forgetting negative prompt**: often the right tool for "not X".

## 🧪 검증 / 중복
- Verified (AUTOMATIC1111 wiki, Compel docs, Midjourney v7 docs 2024-2025, FLUX official guidance).
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — canonical prompt-weight ref + FLUX/T5 caveat |