Downsample register example

.gitignore

@@ -24,3 +24,4 @@ wasm/typescript/demo/
 wasm/test
 micromamba/
 .pixi/
+.vscode/

examples/.gitignore

@@ -0,0 +1,7 @@
+resampled-moving-via-downsample-transform.mha
+resampled-moving.mha
+resampledMoving.mha
+result-downsampled.mha
+result.mha
+result.png
+

examples/downsample-register.mjs

@@ -0,0 +1,118 @@
+#!/usr/bin/env node
+
+/*
+
+This example demonstrates how to use the @itk-wasm/elastix module.
+
+It shows how to:
+
+1. Register with elastix
+2. Apply the resulting transform with transformix
+3. Downsample the input images.
+4. Register the downsampled images.
+5. Apply the resulting transform at the original resolution.
+
+*/
+
+import path from "path";
+
+import { readImageNode, writeImageNode } from "@itk-wasm/image-io";
+import { downsampleNode } from "@itk-wasm/downsample";
+import {
+  elastixNode,
+  defaultParameterMapNode,
+  transformixNode,
+} from "@itk-wasm/elastix";
+
+// ------------------------------------------------------------------
+// Read output input fixed and moving images
+const fixedImagePath = path.join(
+  import.meta.dirname,
+  "data",
+  "CT_2D_head_fixed.mha"
+);
+const movingImagePath = path.join(
+  import.meta.dirname,
+  "data",
+  "CT_2D_head_moving.mha"
+);
+const fixedImage = await readImageNode(fixedImagePath);
+const movingImage = await readImageNode(movingImagePath);
+console.log("Fixed image:", fixedImage);
+console.log("Moving image:", movingImage);
+
+// ------------------------------------------------------------------
+// Perform registration at full resolution
+const { parameterMap: translationParameterMap } = await defaultParameterMapNode(
+  "translation",
+  {
+    numberOfResolutions: 2,
+  }
+);
+const { parameterMap: bsplineParameterMap } = await defaultParameterMapNode(
+  "bspline",
+  {
+    numberOfResolutions: 2,
+  }
+);
+const parameterObject = [translationParameterMap, bsplineParameterMap];
+const { result, transformParameterObject } = await elastixNode(
+  parameterObject,
+  {
+    fixed: fixedImage,
+    moving: movingImage,
+  }
+);
+await writeImageNode(result, "result.mha");
+
+// ------------------------------------------------------------------
+// Use the transform to resample the moving image
+const { result: resampledMovingImage } = await transformixNode(
+  movingImage,
+  transformParameterObject
+);
+// Same as result.mha
+await writeImageNode(resampledMovingImage, "resampled-moving.mha");
+
+// ------------------------------------------------------------------
+// Generate a downsampled version of the fixed and moving images
+const shrinkFactors = [2, 2];
+const { downsampled: downsampledFixedImage } = await downsampleNode(
+  fixedImage,
+  {
+    shrinkFactors,
+  }
+);
+const { downsampled: downsampledMovingImage } = await downsampleNode(
+  movingImage,
+  {
+    shrinkFactors,
+  }
+);
+console.log("Downsampled fixed image:", downsampledFixedImage);
+console.log("Downsampled moving image:", downsampledMovingImage);
+
+// ------------------------------------------------------------------
+// Perform registration at downsampled resolution
+const {
+  result: resultDownsampled,
+  transformParameterObject: transformParameterObjectDownsampled,
+} = await elastixNode(parameterObject, {
+  fixed: downsampledFixedImage,
+  moving: downsampledMovingImage,
+});
+await writeImageNode(resultDownsampled, "result-downsampled.mha");
+
+// ------------------------------------------------------------------
+// Use the transform to resample the moving image at its original resolution
+const { result: resampledMovingImageViaDownsampleTransform } =
+  await transformixNode(movingImage, transformParameterObjectDownsampled, {
+    outputOrigin: fixedImage.origin,
+    outputSpacing: fixedImage.spacing,
+    outputDirection: fixedImage.direction,
+    outputSize: fixedImage.size,
+  });
+await writeImageNode(
+  resampledMovingImageViaDownsampleTransform,
+  "resampled-moving-via-downsample-transform.mha"
+);