Background Change

Background Change enables you to replace image backgrounds while preserving foreground subjects. The endpoint accurately separates the foreground from the background and applies harmonization so the subject blends seamlessly into the new environment.

Model Specifications

Model Name: background-change
Lifecycle: experimental
Processing Time: 12 seconds
Supported Resolution: up to 1.05MP

Request

Replace image backgrounds by submitting the source image and background description to the universal /v1/run endpoint:

POST`https://api.fashn.ai/v1/run`

Request Examples

curl -X POST https://api.fashn.ai/v1/run \
     -H "Content-Type: application/json" \
     -H "Authorization: Bearer YOUR_API_KEY" \
     -d '{
           "model_name": "background-change",
           "inputs": {
             "image": "https://example.com/portrait.jpg",
             "background_prompt": "modern office space with large windows"
           }
         }'

Response

Returns a prediction ID for status polling:

{
  "id": "123a87r9-4129-4bb3-be18-9c9fb5bd7fc1-u1",
  "error": null
}

Request Parameters

Required Parameters

`image`
Required
image URL | base64

Source image containing the subject to preserve. The AI will automatically detect and separate the foreground subject from the background.

Base64 Format

Base64 images must include the proper prefix (e.g., data:image/jpg;base64,<YOUR_BASE64>)

Optional Parameters

`background_prompt`string

Text description of the desired background environment. The AI generates a new background based on this description and harmonizes it with the preserved foreground subject.

Default: Empty string (Natural background for the subject)

`disable_prompt_enhancement`boolean

Disable prompt enhancement for the background description. When true, the background prompt will be used exactly as provided.

Default: false

`seed`integer

Sets random operations to a fixed state. Use the same seed to reproduce results with the same inputs, or different seed to force different results.

Default: 42
Range: 0 to 2^32 - 1

`output_format`'png' | 'jpeg'

Specifies the desired output image format.

-png: Delivers the highest quality image, ideal for use cases such as content creation where quality is paramount.
-jpeg: Provides a faster response with a slightly compressed image, more suitable for real-time applications.

Default: png

`return_base64`boolean

When set to true, the API will return the generated image as a base64-encoded string instead of a CDN URL. The base64 string will be prefixed according to the output_format (e.g., data:image/png;base64,... or data:image/jpeg;base64,...).

This option offers enhanced privacy as user-generated outputs are not stored on our servers when return_base64 is enabled.

Default: false

Response Polling

After submitting your request, poll the status endpoint using the returned prediction ID. See API Fundamentals for complete polling details.

Successful Response

When your background change completes successfully, the status endpoint will return:

{
  "id": "123a87r9-4129-4bb3-be18-9c9fb5bd7fc1-u1",
  "status": "completed",
  "output": [
    "https://cdn.fashn.ai/123a87r9-4129-4bb3-be18-9c9fb5bd7fc1-u1/output_0.png"
  ],
  "error": null
}

The output array contains URLs to your processed images with the new background and harmonized foreground subject.

Runtime Errors

Background Change may encounter the following model-specific errors during processing:

Name Cause Solution

Name	Cause	Solution
`ImageLoadError`	The pipeline was unable to load the input image from the provided inputs.	For Image URLs: Ensure the URL is publicly accessible and not restricted by permissions. Verify that the Content-Type header specifies the correct image format (e.g., image/jpeg, image/png). For Base64-encoded images: Prefix the string with data:image/`format`;base64, where format is the image type (e.g., jpeg, png).
`ThirdPartyError`	A third-party processor failed or refused to handle the request.	Most likely caused by content restrictions enforced by supporting services (e.g., prompt enhancement). If that's the case, try modifying your image inputs or background prompt. If the issue persists across different inputs, contact support@fashn.ai with the prediction ID.
`PipelineError`	An unexpected error occurred during the execution of the pipeline.	Retry the request (you will not be charged for failed attempts). If the issue persists, please reach out to us at support@fashn.ai and include the prediction ID from the failed attempt to help us locate and address the issue promptly.

ImageLoadError

The pipeline was unable to load the input image from the provided inputs.

For Image URLs:

Ensure the URL is publicly accessible and not restricted by permissions.
Verify that the Content-Type header specifies the correct image format (e.g., image/jpeg, image/png).

For Base64-encoded images:

Prefix the string with data:image/format;base64, where format is the image type (e.g., jpeg, png).

ThirdPartyError A third-party processor failed or refused to handle the request. Most likely caused by content restrictions enforced by supporting services (e.g., prompt enhancement). If that's the case, try modifying your image inputs or background prompt. If the issue persists across different inputs, contact support@fashn.ai with the prediction ID.

PipelineError An unexpected error occurred during the execution of the pipeline. Retry the request (you will not be charged for failed attempts). If the issue persists, please reach out to us at support@fashn.ai and include the prediction ID from the failed attempt to help us locate and address the issue promptly.

The Error Object

{
  "error": {
    "name": "PipelineError",
    "message": "Internal server error. If the problem persists, please contact support."
  }
}

Example of an error when polling the /status endpoint:

{
  "id": "123a87r9-4129-4bb3-be18-9c9fb5bd7fc1-u1",
  "status": "failed",
  "error": {
    "name": "ImageLoadError",
    "message": "Error loading input image: The URL's Content-Type is not an image. Content-Type: text/plain;charset=UTF-8"
  }
}

If you encounter an unrecognized error, please contact us at support@fashn.ai.

For detailed implementation guidance and best practices:

Image Preprocessing Best Practices - Optimize your source images for background replacement

Background Change

POSThttps://api.fashn.ai/v1/run

Response

imageRequiredimage URL | base64

background_promptstring

disable_prompt_enhancementboolean

seedinteger

output_format'png' | 'jpeg'

return_base64boolean