Nano Banana 2 Workflow: Converting Vertical Portraits to Horizontal Banners

Social media platforms often demand specific aspect ratios, creating a common challenge for content creators who have high-quality vertical headshots but need horizontal formats for LinkedIn headers, website hero sections, or YouTube thumbnails. Manually cropping these images usually cuts off essential details, while simple stretching distorts the subject's face and body proportions. The solution lies in using generative AI to intelligently expand the canvas. This article outlines a complete workflow for converting vertical social media portraits to horizontal formats using Nano Banana 2, ensuring the subject remains intact while the background is filled contextually.

Understanding the Input Requirements and Model Selection

Before initiating the conversion process, it is crucial to prepare your input assets and select the appropriate model within the Nano Banana ecosystem. The core of this workflow relies on the image-to-image capability, where the tool takes an existing vertical image as a reference and generates a new version with expanded dimensions.

Your primary input is a high-resolution vertical portrait. Ensure the subject is clearly visible and well-lit, as the AI will use these visual cues to extrapolate the surrounding environment. When accessing the generator at Try Nano Banana, you must choose the correct model variant. Google documents Nano Banana 2 as Gemini 3.1 Flash Image (gemini-3.1-flash-image). This model is designed for general-purpose generation and editing tasks. It is important to note that Nano Banana 2 Lite, identified as Gemini 3.1 Flash Lite Image, is focused on speed and cost efficiency. However, it is not optimized for multiple reference inputs or multi-turn sequential editing. Therefore, for a complex task like expanding an image while maintaining subject integrity, Nano Banana 2 Lite should be avoided unless the user accepts significant limitations in quality and control.

The prompt library available on the site offers example prompts that users can copy or adapt. These instructions describe desired outcomes but do not guarantee identity, label, object, or typography preservation. Users should treat any provided text examples as starting points rather than absolute commands. The goal is to instruct the AI to extend the scene naturally, filling the empty space with elements that match the lighting, style, and depth of the original photo.

Step-by-Step Conversion Workflow and Prompt Engineering

Executing the conversion requires a structured approach to ensure the output meets professional standards. Follow this sequence to transform your vertical asset into a horizontal banner.

Step 1: Upload and Configure Dimensions Begin by uploading your vertical portrait to the Nano Banana 2 interface. Select the image-to-image mode. In the settings panel, change the aspect ratio from vertical (e.g., 9:16) to horizontal (e.g., 16:9 or 4:3). The system will automatically create empty space on the left and right sides of the original image. Do not attempt to force the AI to stretch the central figure; instead, rely on its ability to generate new pixels around the existing subject.

Step 2: Craft the Contextual Expansion Prompt The next critical step is writing a prompt that guides the AI on how to fill the new space. A generic prompt like "make it wider" is insufficient. Instead, describe the environment you want to see. For example, if the portrait shows a person against a blurred office background, your prompt might read: "Expand the image horizontally to create a wide banner. Extend the blurred office background seamlessly to both sides. Keep the person centered and unchanged. Add subtle desk elements and bookshelves on the far left and right edges to maintain depth."

This type of prompt helps the AI understand that the subject is fixed while the background is dynamic. Remember that prompt instructions describe desired outcomes; they do not guarantee identity, label, object, or typography preservation. If your image contains text, expect the AI to potentially alter or remove it during the expansion process. Treat all generated results as examples of what is possible rather than guaranteed final outputs.

Step 3: Iterative Refinement If the initial generation looks disjointed, use the multi-turn editing feature if available on your selected plan. You can upload the result back into the tool with a refined prompt, such as "smooth the transition between the original center and the new left edge." Avoid using Nano Banana 2 Lite for this iterative process, as it lacks the optimization for sequential editing required to achieve a polished look.

Checkpoints and Final Export Strategies

Once the generation is complete, perform a series of checks before considering the file ready for publication. First, inspect the subject's face and body for any warping or unnatural distortion. The AI should have kept the central figure identical to the source. Second, examine the newly generated areas for consistency in lighting and texture. The shadows and highlights in the extended background should match the direction and intensity of the original light source. Third, check for artifacts or strange patterns that often appear when AI struggles to blend edges.

If the image passes these checkpoints, proceed to export. Download the file in a high-resolution format suitable for your target platform. Since Nano Banana refers to the AI image generation/editing tool and not a physical product, ensure you are saving the digital file correctly. Finally, integrate the horizontal banner into your design layout. Verify that the composition works well with any overlay text or UI elements you plan to add later.

By following this workflow, you can efficiently adapt vertical content for horizontal spaces without compromising the quality of your original portrait. This method leverages the power of generative AI to solve a common design constraint, allowing for creative flexibility across various social media channels.