Seam melt guide

Overview

Seam melt narrows one picture down to the part you protect, then widens a second picture back out of its own narrow strip.

A pearl-crowned figure before spires, narrowed between dark sides, the figure whole and the spires at its edges thinned
The Subject survives preset past halfway: picture B widening back out between dark sides, the figure whole.

It is an image transition between two pictures, A and B. See picture A and picture B. In the first half of a run A narrows; at halfway the frame switches to B at its narrowest, and in the second half B widens back to full.

It works by seam carving. A seam is a path of one pixel per row from top to bottom, free to bend. The tool removes the seams that matter least first, and pushes what is left together in the middle of the frame. The sides it frees show the dark frame colour.

What matters is scored in an energy map: the strength of the edges in the picture's luminance, found with a Sobel operator. Plain areas are a low-energy region, and go first. The cheapest seams are found row by row with dynamic programming over the cumulative energy.

Seams only run top to bottom, so a picture only ever gets narrower, never shorter. See vertical seam.

The spot you tap is protected: seams steer around it, so the subject there survives longest. See subject protection. After each run the direction flips: the next run carries B back into A.

Four presets set every slider at once: Digest, Subject survives, Accordion and Squeeze cut. You can swap in your own two pictures, and keep a PNG or a video.

Open Seam melt Start here

In this guide

  1. StartWhat you need and your first melt in five steps.
  2. Every controlEvery control in the panel, one line each.
  3. Three looksThree presets caught mid-melt, and how each was made.
  4. Keep your workThe PNG and the video.
  5. HelpWhat to do when something goes wrong.

The seams are worked out on your computer's processor ahead of time, for 48 stages of the melt; the GPU then only looks up where each column comes from, in a fragment shader. It runs in your browser with WebGL. Your pictures stay on your device and nothing is uploaded. A mouse, a trackpad, a pen and a finger all work.