Relight a photo with AI: change the light, keep the shot

To relight a photo with AI, give an image-edit model the original photo and a prompt that describes only the new light (where it comes from, how soft it is, its color, the time of day) and says that everything else stays the same. The model draws a new version of the picture as if it had been lit that way, so check the result against the original.

The request below uses Sume's Image API docs, read on 2026-09-28.

What is a relight?

A relight changes a photo's lighting after it was taken. In a studio, that means reshooting with the lamps moved. In editing software, it means painting light and shadow by hand. AI relighting does it generatively: the model reads the scene from your photo and draws a new version with the light you describe. The parts you can describe:

• Direction: from the left, from above, from behind (a rim light).
• Quality: soft and diffused, or hard with crisp shadows.
• Color: warm golden hour, cool daylight, a colored gel.
• Mood: bright and even for a catalog, low and moody for a campaign.

How do I relight a photo with AI?

Host the photo at a public HTTPS URL and send it in input_references to POST /v1/images, on a model that takes references. On edit calls, the docs advise aspect_ratio: "auto" to match the reference; leaving the field out is not the same. Ask for a few versions with n.

curl -X POST "https://api.sume.com/v1/images" \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "openai/gpt-image-2.5",
    "prompt": "Relight this photo with warm, low evening sun from the left, casting long soft shadows to the right. Keep the product, its label, its colors, the table, and the framing exactly the same.",
    "input_references": [
      { "type": "image_url", "image_url": { "url": "https://example.com/photo.jpg" } }
    ],
    "aspect_ratio": "auto",
    "n": 3
  }'

What should a relight prompt say?

Name the light, then list what must not change. AI photo editing prompts covers the change-one-thing pattern; for relighting, three examples:

• Product: “Relight with a large soft light from above and a thin rim light from behind; keep the bottle, label, and white background the same.”
• Portrait: “Relight with soft window light from the right and a gentle fill; keep the face, expression, hair, and clothing the same.”
• Room: “Relight as late afternoon with warm sun through the window; keep the furniture, layout, and colors the same.”

Will the rest of the photo stay the same?

Not guaranteed. The model produces a new image, so text on a label, fine texture, and faces can drift, and new shadows may not match the geometry of the scene. Compare each version with the original and keep the original file. ChatGPT Image 2.5 also takes an optional mask_url on edits, but the docs don't describe what the mask image should contain, so name the area in the prompt instead.

How much does it cost, and what are the limits?

Relighting is an ordinary image edit, billed per completed image.