> ## Documentation Index
> Fetch the complete documentation index at: https://docs.pulze.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Merge Region Renders

> Blend a re-rendered region of your image into the existing render element layers, cropped by a mask.

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.

## 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](https://mintcdn.com/sourcelinekft/z3vWbLeBmT4OoYjW/images/layerwise/lw_region_concept.webp?fit=max\&auto=format\&n=z3vWbLeBmT4OoYjW\&q=85\&s=56b9b6d96184ba765dcdf7ab68dc27a8)

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

## 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](https://docs.pulze.io/layerwise/workflows/update-renders.md). 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](https://mintcdn.com/sourcelinekft/z3vWbLeBmT4OoYjW/images/layerwise/lw_region_dialog.webp?fit=max\&auto=format\&n=z3vWbLeBmT4OoYjW\&q=85\&s=bf4fb7489f9358343cf298f357078dfa)

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.

## 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](https://mintcdn.com/sourcelinekft/z3vWbLeBmT4OoYjW/images/layerwise/lw_region_result.webp?fit=max\&auto=format\&n=z3vWbLeBmT4OoYjW\&q=85\&s=26496bce40e67849d3e49cf00ce443d3)

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

> [!TIP]
>
> 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.


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