How to Return NumPy Arrays as Images Using FastAPI?

How to Render a NumPy Array as an Image in FastAPI

Issue: Displaying a NumPy array as an image in FastAPI

Solution:

To display a NumPy array as an image in FastAPI, you have two main options:

Option 1: Return Image as Bytes

This approach involves converting the NumPy array into bytes using either the PIL or OpenCV library and then returning the bytes as a custom Response with the appropriate headers.

Using PIL:

<code class="python"># Convert NumPy array to bytes using PIL
from PIL import Image
import io

arr = np.zeros((512, 512, 3), dtype=np.uint8)  # Sample RGB image
buf = BytesIO()
im = Image.fromarray(arr)
im.save(buf, format='PNG')
im_bytes = buf.getvalue()

# Return bytes as a Response with appropriate headers
from fastapi import Response

headers = {'Content-Disposition': 'inline; filename="test.png"'}
return Response(im_bytes, headers=headers, media_type='image/png')</code>

Using OpenCV:

<code class="python"># Convert NumPy array to bytes using OpenCV
import cv2

arr = np.zeros((512, 512, 3), dtype=np.uint8)  # Sample RGB image
arr = cv2.cvtColor(arr, cv2.COLOR_RGB2BGR)
success, im = cv2.imencode('.png', arr)

# Return bytes as a Response with appropriate headers
from fastapi import Response

headers = {'Content-Disposition': 'inline; filename="test.png"'}
return Response(im.tobytes(), headers=headers, media_type='image/png')</code>

Option 2: Return Image as JSON-encoded NumPy Array

This approach is not recommended for display purposes but can be used for data transfer.

Using PIL:

<code class="python">import numpy as np
import json

# Convert NumPy array to JSON-encoded string
arr = np.zeros((512, 512, 3), dtype=np.uint8)  # Sample RGB image
json_data = json.dumps(arr.tolist())</code>

Using OpenCV:

<code class="python">import numpy as np
import cv2
import json

# Convert NumPy array to JSON-encoded string
arr = np.zeros((512, 512, 3), dtype=np.uint8)  # Sample RGB image
json_data = json.dumps(arr.tolist()).replace('-1', '255')</code>

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