How to Display NumPy Arrays as Images in FastAPI?

Render NumPy Array as Image in FastAPI

Introduction

FastAPI is a popular Python framework for building APIs. It provides a convenient way to handle HTTP requests and responses. This article demonstrates how to render NumPy arrays as images in FastAPI.

Option 1: Return Image as Bytes

Using PIL

<code class="python">from PIL import Image
from io import BytesIO

@app.get("/image", response_class=Response)
def get_image():
    arr = np.zeros((512, 512, 3), dtype=np.uint8)
    arr[0:256, 0:256] = [255, 0, 0]  # Red patch in the upper left
    im = Image.fromarray(arr)

    with io.BytesIO() as buf:
        im.save(buf, format='PNG')
        im_bytes = buf.getvalue()

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

Using OpenCV

<code class="python">import cv2

@app.get("/image", response_class=Response)
def get_image():
    arr = np.zeros((512, 512, 3), dtype=np.uint8)
    arr[0:256, 0:256] = [255, 0, 0]  # Red patch in the upper left
    arr = cv2.cvtColor(arr, cv2.COLOR_RGB2BGR)  # OpenCV uses BGR

    success, im = cv2.imencode('.png', arr)
    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

Note: Use this option only for converting and sending the image as a JavaScript object.

Using PIL

<code class="python">import json

@app.get("/image")
def get_image():
    im = Image.open('test.png')
    arr = np.asarray(im)
    return json.dumps(arr.tolist())</code>

Using OpenCV

<code class="python">@app.get("/image")
def get_image():
    arr = cv2.imread('test.png')
    return json.dumps(arr.tolist())</code>

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