Returning a base64 encoded image from a Svelte Kit endpoint

#SvelteKit return image from endpoint

How to return a base64 encoded image from a Svelte Kit endpoint.
This example has the /routes/[slug].png.ts route dynamic but doesn't do anything with the slug. 
This is where you could do some fancy image generation based on the slug.

[slug].png.ts

export async function get({params}) {
 // do some cool image generation with the params
 const imageData =
  'iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg==';
 const image = Buffer.from(imageData, 'base64');
 return {
  'Content-Type': 'image/png',
  'Content-Length': image.length,
  body: image
 };
}

Thanks!

I need to do this for images saved on $lib/server/