Photo overlay: what it is
Quick facts
- Definition
- Technique of placing one image over another, with transparency, to check alignment or compare two photos.
- Also called
- Overlay, superimposition, reference transparency.
- Use in facial harmonization
- Repeat the framing of the before photo at the follow-up and compare changes without positioning error.
- Requires
- Same distance, same light, same pose and same expression in both images.
- Limit
- It does not prove a result on its own: any difference in pose alters the comparison.
Photo overlay is the technique of displaying one image over another with some transparency. In facial harmonization it has two main uses: helping to repeat the framing of a reference photo (for example, the "before" photo when photographing the follow-up) and visually checking what changed between two moments. The value of the technique lies in reducing positioning error, which is the greatest enemy of an honest comparison.
Why does alignment matter so much?
A slight head tilt, a slightly raised chin or a photo taken closer changes the look of the lips, cheekbone, nose and chin. Without a guide, the difference between two photos mixes what the procedure did with what the pose did. Overlay lets you align facial landmarks, such as the pupils, the base of the nose and the corners of the mouth, before taking the photo.
What must be the same in both images?
| Factor | Why it matters |
|---|---|
| Distance and lens | Focal length and proximity change proportions, especially of the nose and lips |
| Light | Diffuse lighting and the same direction avoid shadows that mimic volume |
| Pose | Level head and gaze on the horizon, same camera height |
| Expression | Rest with rest, smile with smile |
Overlay and Harmy
In the app's actual result feature, guided capture shows the "before" photo in transparency over the camera, which is exactly a guide overlay. Once captured, the result photo is aligned by the eyes, and the app lets you compare Projection, Actual result and Projection vs Actual.
Limits of the technique
Overlay helps reduce pose error, but it does not eliminate differences in swelling, light, makeup or time. That is why the comparison should record the date, the interval since the procedure and the conditions of the photo. For side-by-side comparison practice, see also the before and after slider.
Also called: overlay, reference transparency, onion skin.
Frequently asked questions
Is overlay the same as the before and after slider?
No. Overlay places a translucent image over the other to align or check; the slider reveals one image in place of the other when a line is dragged. Both serve comparison, with different purposes.