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Resize

Resize makes a copy of an image at any new resolution by interpolation: coarser, to fit a large sample into a simulation, or finer, to give a solver more voxels across thin throats. A binary image keeps its porosity.

  • Find it Tools › Preparation › Resize
  • Needs a 3D image, binary or greyscale
  • Returns a copy at the new resolution, with the voxel size scaled to match; binary stays binary with the same porosity, greyscale comes back as fractional intensities
  • Runs on CPU
  • Science Resize

Run it

  1. Open Tools, then Preparation, and select Resize.
  2. Under Source, choose the Source image.
  3. Under Settings, set the Zoom factor: below 1 shrinks the image, above 1 enlarges it. Below the settings, the page shows the output's dimensions, number of voxels, data type and voxel size.
  4. On the right, the Slice preview compares a slice of the original with the same slice resized. Pick the Plane and Slice index to look at. The preview resizes one slice only, so it's an approximation; it creates no image.
  5. Under Output, choose Save as New and a New image name, or Overwrite Original.
  6. Select Run. The job page opens and links to the new image when it's done.

The Resize page with a zoom factor of 0.5, its output size and a slice preview.

A zoom factor of 0.5, the output size and a slice preview.

Settings

Setting Default Range What it does
Source image your team's ready images The image to resize.
Zoom factor 0.5 more than 0 The scale along every axis. Each side of \(N\) voxels becomes \(N\) times the factor, rounded to the nearest whole number.
Plane XY XY, XZ, YZ The slice the preview shows.
Slice index the middle slice within the image Which slice of that plane the preview shows.
Save mode Save as New Save as New, Overwrite Original Whether to keep the original and add a resized copy, or replace it.
New image name the image's name with _resized up to 200 characters Save as New only.

Whether the image is resized as binary or greyscale follows from its values: a segmented image, 0/1 or 0/255 alike, is resized as binary and comes back as a boolean image; any other image is resized as greyscale.

Results

The job page shows the Resized image table: the Source, Method, Output dimensions, Voxel size at creation, Zoom factor and Interpolation order. For a binary image it adds the Source porosity, Output porosity and Porosity error, with the Target pore count and Actual pore count; for a greyscale image, the Output data type. An Output image panel links to the new image.

A small example: a 100³ synthetic sample reduced four times along each side, by Downsample and by Resize (zoom factor 0.25). Resizing filters and interpolates first, then keeps porosity. The subtitles give each result's porosity and its number of separate solid clusters: neither method guarantees the source's connectivity.

In progress

Screenshot: a completed Resize job page for a binary image. Arrows to the Output porosity, Porosity error and Actual pore count rows of the Resized image table, and the View output image button.

Common problems

  • The greyscale result is fractional. A greyscale image keeps its interpolated intensities as decimals. Segment the resized image afterwards.
  • Enlarging didn't add detail. Upsampling adds voxels, not information: throats get more voxels across, but their shape is only as good as the original scan.
  • Connectivity or transport changed. Resizing keeps porosity, not connectivity, surface area or transport properties. Compare a key result on both images before relying on the copy.
  • The image is too large. The page says, below the settings, when the image or its output is beyond what Resize takes. Trim or downsample it first.
  • Overwrite Original is refused. The image has jobs running on it. Wait for them to finish, or save as new.

Science

How the filter, the interpolation and the porosity-preserving step work: Resizing in the Scientific reference.