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The Nano Banana Prompting Manual
Expert's Guide to Mastering Gemini 2.5 Flash Image
Piotr Macai
September 03, 2025
Table of Contents
The Nano Banana Prompting Manual: An Expert's Guide to Mastering Gemini 2.5 Flash Image
Welcome to the "Nano Banana" era of image generation!
Chapter 1: The New Frontier of Creative AI — An Introduction to Gemini 2.5 Flash Image
1.1. Deconstructing the Codename: "Nano Banana" Explained
Welcome to the "Nano Banana" era of image generation. While its official name, Gemini, suggests a serious scientific tool, the viral codename "Nano Banana" caught on for a reason: this model quietly fixed the biggest headaches for creators, like making sure a character's face stays the same across multiple images and generating perfect, readable text. Before Google officially announced it, the model appeared anonymously on a testing site and quickly shot to the top of the charts, creating a buzz that the company leaned into by using banana emojis on social media.
1.2. The Core Value Proposition: A Paradigm Shift in Image Generation
Gemini 2.5 Flash Image is a "state of the art" (SOTA) tool that redefines what’s possible in AI image generation and editing. Its core promise is to give you higher-quality images and more powerful creative control.
What really sets it apart is its speed and a remarkable ability to keep cross-edit coherence, meaning it preserves details and the overall feel of a scene even after multiple changes.
This isn't just a minor improvement; it changes the entire creative process. Instead of the old "prompt, wait, regenerate" cycle, you're now in a fluid, back-and-forth conversation with the AI.
Now you can visualize and refine ideas in near real-time, making the process feel less like a chore and more like a collaboration. This efficiency, combined with its advanced editing capabilities, positions the model as a genuine alternative to traditional image editing software, providing a powerful, conversation-based alternative for professionals.
Chapter 2: The Foundational Principles — Understanding the Model's "Mindset"
2.1. Unpacking the Leaked System Prompt
To truly master Gemini 2.5 Flash, it helps to peek under the hood at its core directives. A set of internal instructions, often called the leaked system prompt, reveals the model’s operational philosophy. Here are the key principles that govern its behavior:
Assume Technical Capability: This is the model’s "can-do" attitude. Instead of questioning whether a request is possible, the model is told to assume it can achieve the desired result, no matter how complex the prompt sounds. This directive encourages it to be bold and try to execute even the most intricate requests.
The Depiction Protocol: This is the "show, don't judge" rule. The model is strictly instructed to "show what's asked, not to decide if it's 'good' or 'bad' or 'right' or 'wrong'". This overriding directive positions it as a pure execution engine, delivering exactly what the user asks for without subjective commentary or imposed style.
Defer Content Judgment: The model is not the "safety police". It's designed to send user requests to a separate safety team for review. This separation of concerns allows the model to focus on its primary task-creating images-while a distinct system handles content moderation.
Forbidden Response Pattern: If the model gets confused, this rule prevents it from hitting a dead end or providing an error message. It's designed to always provide a useful response, even if it's unsure, ensuring a smoother user experience.
You do not need to write a description: This is a clever efficiency trick. The model's image tool is smart enough to understand the full context of the conversation without the model needing to explicitly describe the image in its response. This makes the conversation feel more natural and fluid.
Conversational text around the tag: This simple instruction encourages the model to use friendly, natural language, making the interaction feel more like a conversation with a helpful assistant than a technical transaction with a robot.
In short, these directives create a predictable and user-focused dynamic. The model is built to be a literal executor of your instructions, which is a powerful asset for anyone who needs precise control over their output.
2.2. The Golden Rule of Prompting: Narrative over Keywords
Forget the old days of cramming your prompts with keywords. The single most important principle for success with Gemini 2.5 Flash is to use a descriptive, narrative style. The model’s strength is its "deep language understanding," so a well-structured paragraph will consistently outperform a disconnected list of words.
To get the best results, always include the core elements:
subject, composition, action, location, style.
It's also a good idea to avoid using figurative language to ensure your intent is perfectly clear.
This approach gives the model a detailed blueprint to follow. For instance, to create a photorealistic image, you should provide the kind of details a photographer would consider:
A photorealistic close-up portrait of an elderly Japanese ceramicist with deep, sun-etched wrinkles and a warm, knowing smile. He is carefully inspecting a freshly glazed tea bowl. The setting is his rustic, sun-drenched workshop. The scene is illuminated by soft, golden hour light streaming through a window, highlighting the fine texture of the clay. Captured with an 85mm portrait lens, resulting in a soft, blurred background (bokeh). The overall mood is serene and masterful. Vertical portrait orientation.
This comprehensive prompt gives the model all the information it needs to produce a high-fidelity image that matches your vision.
Chapter 3: The Prompting Toolkit — Strategies for High-Quality Output
3.1. Crafting Photorealistic Scenes: The Photographer's Eye
Prompt: A photorealistic close-up portrait of an young Polish woman, walking through the small village, in style of 1950' photography
To get a realistic result, you need to think like a photographer. The model is highly responsive to photography-related terms. Your prompt should include details about:
Shot type:
close-up,wide shotSubject and Action:
an elderly Japanese ceramicist,carefully inspecting a freshly glazed tea bowlEnvironment and Lighting:
rustic, sun-drenched workshop,soft, golden hour lightCamera/Lens Details:
85mm portrait lens,blurred background (bokeh)Aspect Ratio:
vertical portrait orientation
By including this level of technical detail, you can guide the model to create professional-grade outputs. This shows that the model's training data includes a wealth of professionally tagged images, allowing it to accurately replicate the look and feel of high-end photography.
 | Prompt: Prompt: A photorealistic close-up portrait of an young Polish woman, walking through the small village, in style of 1950' photography |
3.2. Generating Stylized Illustrations and Assets
When your goal is a non-photorealistic image, like an illustration or a sticker, the strategy shifts to focusing on artistic style and design elements. Be explicit about the aesthetic you want. Key elements to include are:
Style:
kawaii-style,3D animation,watercolor paintingKey Characteristics:
happy red panda wearing a tiny bamboo hatColor Palette:
vibrant color paletteLine and Shading Style:
bold, clean outlines,simple cel-shadingBackground:
transparentorwhite
A common template for this is: A [style] sticker of a [subject], featuring [key characteristics] and a [color palette]. The design should have [line style] and [shading style]. The background must be [background type]. This is a fantastic approach for social media creators and designers who need a consistent look across a series of graphics.
 | Prompt: A ghibli-style sticker of a happy bear wearing a tiny bamboo hat. It's munching on a green bamboo leaf. The design features bold, clean outlines, simple cel-shading, and a vibrant color palette. The background must be white. |