Subsampling images

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The subsample algorithm in MIPAV allows you to reduce an image in size by a factor of 2, 4, or 8 times. Each pixel of the subsampled image is a Gaussian-weighted average of the original image's 8 neighboring pixels for 2D images or 26 neighboring voxels for 3D images. For example, subsampling a 3D image with the x, y, and z dimensions of 256 x 256 x 32, respectively, by a factor of 2 produces a new image with x, y, and z dimensions of 128 x 128 x 16, respectively.

To subsample the images

  1. Open an image (Figure 1).
  2. Select Algorithms>Transformation tools > Subsample. The Subsample dialog box (Figure 2) opens.




.

Figure 1. Original image before subsampling

ExampleEyeOriginalBeforeSubsampling.jpg
  1. Select one of the following:
      • Subsample by 2
      • Subsample by 4
      • Subsample by 8
      • Select, as an option for 2.5D images only, the Process each slice independently (2.5D) check box.

    Tipicon.gif

    Tip: If you are not working with 2.5D images, the Process each slice independently (2.5D) check box does not appear in the Subsample dialog box.


  2. Click OK. A status message appears briefly while the program generates the subsampled image in a new image window.









    Figure 2. Subsample dialog box

    Subsample by 2
    Subsamples each image dimension by a factor of 2.
    Subsamplegd.jpg
    Subsample by 4
    Subsamples each image dimension by a factor of 4.
    Subsample by 8
    Subsamples each image dimension by a factor of 8.
    Process each slice independently (2.5D)
    Filters each slice of the dataset independently of adjacent slices.
    OK
    Applies the parameters that you specified to subsample the image.
    Cancel
    Disregards any changes you made in this dialog box, closes the dialog box, and does not subsample the image.
    Help
    Displays online help for this dialog box.

    Figure 3. An image subsampled by 2, by 4, and then by 8

    ExampleSubsampledEyes.jpg