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Sometimes only part of the image changes: a new sofa, a fixed material, a noisy corner. Instead of re-rendering the full frame, render only that region with the same render elements. Merge as regions puts each region render on top of its element’s existing layer, cut out by a mask, and leaves the rest of the image as it was.

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What you need

  • The PSD with its render element layers, open in Photoshop.
  • The region renders: the same elements, rendered at the full image size with only the region filled in (the usual output of a region render in V-Ray, Corona or FStorm).
  • Ideally a mask for the region, typically the region render’s Alpha pass. Its white area is what gets merged.
The original render, a region render, its alpha, and the merged result

A region render and its alpha, merged into the full image

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Merge the regions

1

Start Update renders

With the PSD open, press Update renders on Home and pick the region renders, as in Update renders. Include the region’s Alpha file in your pick.
2

Check the pairing

In the plan, check that each layer has its region render, and turn off the ones you don’t want to merge.
3

Press Merge as regions

The Merge as regions dialog asks for a Region mask. Choose the region’s Alpha file from the list (you can use any of the picked files).
4

Merge

Press Merge regions. Each layer is updated as its own undo step.
The Region mask dialog listing the picked render files

Choosing the mask that crops the regions

If you choose None, merge uncropped, LayerWise asks you to confirm: without a mask, the region renders are merged whole, and their black areas cover the old image.

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What happens

  • The mask file becomes a channel named regionAlphaMask in the document. It stays there, so you can reuse it as a selection.
  • For each layer, the region render is placed above it, masked by the region channel, and both are combined into a single smart object. Inside it is the old render with the region on top.
  • The layer’s name, opacity, blend mode, visibility, mask, smart filters and layer styles move to the new smart object, so it looks and behaves as before.
The plan’s Resize and mask options work as in a normal update. Keep each layer’s current size and position isn’t used when merging regions.
The Layers panel after merging regions, and the contents of a merged smart object

Each merged layer holds the old render with the masked region on top

You can merge several regions over time: each merge adds a new region on top inside the smart object, and the older regions stay inside.