プロンプトエンジニアリング基礎

import os
import sys
from datetime import datetime
from dotenv import load_dotenv
from google import genai
from google.genai import types
from PIL import Image
import io

def generate_image(prompt, output_filename=None, aspect_ratio="1:1"):
    """プロンプトから画像を生成する

    Args:
        prompt: 画像生成プロンプト
        output_filename: 出力ファイル名（省略時はタイムスタンプ）
        aspect_ratio: アスペクト比（"1:1", "16:9", "9:16", "3:4", "4:3"）
    """

    load_dotenv()
    client = genai.Client(api_key=os.getenv("GOOGLE_API_KEY"))

    print(f"プロンプト: {prompt[:50]}..." if len(prompt) > 50 else f"プロンプト: {prompt}")
    print(f"アスペクト比: {aspect_ratio}")
    print("生成中...")

    response = client.models.generate_content(
        model="gemini-2.5-flash-image",
        contents=prompt,
        config=types.GenerateContentConfig(
            response_modalities=['IMAGE'],
            image_config=types.ImageConfig(aspect_ratio=aspect_ratio)
        )
    )

    for part in response.candidates[0].content.parts:
        if hasattr(part, 'inline_data'):
            image = Image.open(io.BytesIO(part.inline_data.data))

            # ファイル名が指定されていなければタイムスタンプで生成
            if output_filename is None:
                timestamp = datetime.now().strftime("%Y%m%d_%H%M%S")
                output_filename = f"generated_{timestamp}.png"

            image.save(output_filename)
            print(f"画像を保存しました: {output_filename}")
            return image

    print("画像の生成に失敗しました")
    return None

if __name__ == "__main__":
    if len(sys.argv) < 2:
        print("使い方: python generate_image.py \"プロンプト\" [出力ファイル名] [アスペクト比]")
        print("")
        print("例:")
        print('  python generate_image.py "A cute cat"')
        print('  python generate_image.py "A cute cat" cat.png')
        print('  python generate_image.py "A cute cat" cat.png 16:9')
        print("")
        print("アスペクト比: 1:1（デフォルト）, 16:9, 9:16, 3:4, 4:3")
        sys.exit(1)

    prompt = sys.argv[1]
    output = sys.argv[2] if len(sys.argv) > 2 else None
    ratio = sys.argv[3] if len(sys.argv) > 3 else "1:1"

    generate_image(prompt, output, ratio)

pip install pillow

# 基本
python generate_image.py "プロンプト"

# ファイル名指定
python generate_image.py "プロンプト" output.png

# アスペクト比指定（縦長）
python generate_image.py "プロンプト" output.png 3:4

cat, window, rain, cozy, warm light

A fluffy orange tabby cat sits contentedly on a cushioned window sill,
watching raindrops trace paths down the glass. The warm glow of a
nearby lamp casts soft amber highlights on the cat's fur, while the
grey afternoon light filters through the rain-streaked window.

A photorealistic close-up portrait of a young woman with warm brown eyes.
Shot with an 85mm portrait lens, f/2.8 aperture, shallow depth of field.
Soft natural window light from the left side creates gentle shadows.
Background is a blurred garden with beautiful bokeh.

A modern glass skyscraper photographed from a low-angle perspective,
shot with a wide-angle lens. The building towers against a dramatic
cloudy sky at golden hour. Deep depth of field captures both the
building and the dramatic clouds in sharp focus.

A small cottage nestled between two ancient oak trees,
with a winding path leading to its door in the foreground,
and misty mountains visible in the background.

Golden hour sunlight streaming through the window,
casting long warm shadows across the wooden floor,
with soft ambient light filling the room.

Cherry blossom petals drifting in the gentle spring breeze,
a few petals swirling around the young woman's feet,
her hair rustling softly in the wind.

A cozy bookshop interior with floor-to-ceiling shelves.
An elderly man sits in a leather armchair beside the window,
reading a worn book. Dust particles float in the warm afternoon
sunlight streaming through the tall windows. Books are stacked
precariously on a small table in the foreground, while more
shelves recede into shadow in the background.

[Subject Identity]: A [age]-year-old [ethnicity] [gender] with [hair] and [features].
[Professional Context]: [use case / style].
[Clothing & Styling]: Wearing [detailed clothing description].
[Expression & Pose]: [expression], [pose description].
[Lighting Setup]: [lighting type and direction].
[Background]: [background description].
[Technical Specs]: [camera/lens specs].

A confident 35-year-old Japanese businessman in a professional headshot.
Wearing a tailored charcoal suit with a subtle pinstripe, crisp white
dress shirt, and burgundy silk tie.
Expression: Subtle confident smile with direct eye contact.
Posture: Slight squared shoulders projecting professionalism.
Lighting: Soft diffused front lighting eliminating harsh shadows,
with subtle rim light separating subject from background.
Background: Neutral gray studio gradient.
Technical: 85mm portrait lens, f/2.8 aperture, sharp facial details
with smooth background bokeh.

A fierce elven warrior princess in a fantasy character portrait.
She has long silver braided hair, sharp pointed ears, and piercing
emerald green eyes with a determined gaze.
Wearing ornate silver plate armor with intricate gold filigree,
a flowing deep blue cape, and a jeweled circlet crown.
Expression: Determined and noble, chin slightly raised.
Lighting: Dramatic golden hour backlighting with soft fill light
on her face, creating a heroic silhouette.
Background: Misty forest clearing with light rays streaming through
ancient trees.
Technical: Medium shot, slight low-angle perspective for heroic feel.

no cars, --no blur, no people

A red apple on a table, no background objects, no other fruits,
--no blur, no shadows

A single red apple centered on a pristine white marble surface.
The background is pure white, completely empty and seamless.
Sharp focus throughout with even studio lighting,
no shadows, creating a clean product photography aesthetic.

ステップ1: 基本構図を生成
           ↓
ステップ2: 単一変数を調整（例：照明のみ変更）
           ↓
ステップ3: 別の変数を調整（例：表情のみ変更）
           ↓
ステップ4: 最終調整

A young woman sitting at a cafe table with a cup of coffee.

A young woman sitting at a cafe table with a cup of coffee.
Warm afternoon sunlight streaming through the window,
creating soft shadows and a cozy atmosphere.

A young woman with shoulder-length brown hair sitting at a
rustic wooden cafe table. She holds a ceramic cup of steaming
coffee, looking thoughtfully out the window.
Warm afternoon sunlight streaming through the window,
creating soft shadows and a cozy atmosphere.
Shot with an 85mm lens, shallow depth of field.

A young woman with shoulder-length brown hair sitting at a
rustic wooden cafe table in a cozy Parisian-style coffee shop.
She holds a ceramic cup of steaming coffee, looking thoughtfully
out the rain-streaked window with a gentle smile.
Warm afternoon sunlight mixed with soft ambient cafe lighting,
creating an intimate, contemplative atmosphere.
Background shows blurred bookshelves and vintage decor.
Shot with an 85mm lens, f/2.0, shallow depth of field,
film-like color grading with warm tones.

A majestic dragon with shimmering crimson scales soars through
the sky above jagged mountain peaks. Its powerful wings are
spread wide, catching the warm golden light of the setting sun.
The dragon is silhouetted against a dramatic orange and purple
sunset sky, with wisps of clouds swirling around its body as it
glides majestically over the misty valleys below.

[Subject Identity]: A beautifully arranged kaiseki course featuring
seasonal sashimi, grilled fish, and colorful vegetable dishes.
[Professional Context]: High-end Japanese restaurant promotional
photography for magazine advertisement.
[Styling]: Traditional ceramic plates and lacquerware arranged on
a dark wooden counter, garnished with shiso leaves and edible flowers.
[Composition]: Overhead shot with slight angle, showcasing the
artful arrangement of multiple dishes.
[Lighting Setup]: Soft natural window light from the left, with
subtle warm accent lighting highlighting the food's freshness.
[Background]: Blurred traditional Japanese interior with
paper screens and bamboo elements.
[Technical Specs]: 50mm macro lens, f/4, sharp focus on center dish
with gentle depth falloff on surrounding plates.

A cat sleeping on a sofa. Warm afternoon sunlight streaming
through nearby windows, casting soft golden highlights on
the cat's fur.

A fluffy orange tabby cat curled up peacefully on a plush
velvet sofa. Warm afternoon sunlight streaming through nearby
windows, casting soft golden highlights on the cat's fur.
Its eyes are gently closed, one paw tucked under its chin.

A fluffy orange tabby cat curled up peacefully on a plush
emerald green velvet sofa in a cozy living room. Warm afternoon
sunlight streaming through sheer curtains, casting soft golden
highlights on the cat's fur. Its eyes are gently closed, one paw
tucked under its chin. Background shows blurred bookshelves and
houseplants. Shot with an 85mm lens, f/2.0, shallow depth of field,
creating a dreamy, intimate atmosphere.