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Downsample[array,n]

returns a downsampled version of the array by sampling every n^(th) element.

Downsample[array,n,offset]

starts sampling from the element at position offset.

Downsample[image,…]

downsamples an image.

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Downsample

Downsample[array,n]

returns a downsampled version of the array by sampling every n^(th) element.

Downsample[array,n,offset]

starts sampling from the element at position offset.

Downsample[image,…]

downsamples an image.

Details

  • In Downsample[array,…], array can be an array of any rank.
  • Downsample works with arrays of any rank and 2D and 3D images.
  • Downsample[array,{n1,n2,…}] samples every ni^(th) element in the i^(th) dimension.
  • Downsample[array,n] is equivalent to Downsample[array,n,1].
  • In Downsample[array,n,offset], the offset has to be an integer between 1 and n.

Examples

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Basic Examples  (4)

Downsample a list by a factor of 2:

Wolfram Language code: Downsample[Range[10], 2]

Downsample a 2D array:

Wolfram Language code: Downsample[(⁠| | | | | - | - | - | | 1 | 2 | 3 | | 4 | 5 | 6 | | 7 | 8 | 9 |⁠), 2]//MatrixForm

Downsample an image by a factor of 2:

Wolfram Language code: Downsample[[image], 2]

Downsample a 3D image:

Wolfram Language code: i = Image3D[ExampleData[{"TestImage3D", "CTengine"}], ImageSize -> All]
Wolfram Language code: Downsample[i, 2]

Scope  (4)

Downsample a list by a factor of 3:

Wolfram Language code: Downsample[Range[10], 3]

Use an offset:

Wolfram Language code: Downsample[Range[10], 3, 2]

Use a different downsampling factor in each dimension:

Wolfram Language code: Downsample[(⁠| | | | | - | - | - | | 1 | 2 | 3 | | 4 | 5 | 6 | | 7 | 8 | 9 |⁠), {1, 2}]//MatrixForm

Downsample a symbolic array:

Wolfram Language code: Downsample[{a, b, c, d, e, f}, 2]

Downsample an image:

Wolfram Language code: Downsample[[image], 2]

Downsample using an offset of 2:

Wolfram Language code: Downsample[[image], 2, 2]

Applications  (2)

Create an image pyramid using iterative blurring and downsampling:

Wolfram Language code: i = [image];
Wolfram Language code: NestList[Downsample[Blur[#, 1], 2]&, i, 4]

Use a smoothing filter to downsample a signal:

Wolfram Language code: q = {(1/4), (1/4), (1/4), (1/4)};
Wolfram Language code: list = RandomReal[1, 16];
Wolfram Language code: res1 = Downsample[ListConvolve[q, list], 2]

A faster implementation would add convolutions on the downsampled signal and downsampled filter:

Wolfram Language code: res2 = ListConvolve[Downsample[q, 2], Downsample[list, 2]]
Wolfram Language code: res3 = ListConvolve[Downsample[q, 2, 2], Downsample[list, 2, 2]]
Wolfram Language code: res4 = res2 + res3
Wolfram Language code: res1 - res4
Wolfram Research (2012), Downsample, Wolfram Language function, https://reference.wolfram.com/language/ref/Downsample.html (updated 2016).

Text

Wolfram Research (2012), Downsample, Wolfram Language function, https://reference.wolfram.com/language/ref/Downsample.html (updated 2016).

CMS

Wolfram Language. 2012. "Downsample." Wolfram Language & System Documentation Center. Wolfram Research. Last Modified 2016. https://reference.wolfram.com/language/ref/Downsample.html.

APA

Wolfram Language. (2012). Downsample. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/Downsample.html

BibTeX

@misc{reference.wolfram_2026_downsample, author="Wolfram Research", title="{Downsample}", year="2016", howpublished="\url{https://reference.wolfram.com/language/ref/Downsample.html}", note=[Accessed: 12-June-2026]}

BibLaTeX

@online{reference.wolfram_2026_downsample, organization={Wolfram Research}, title={Downsample}, year={2016}, url={https://reference.wolfram.com/language/ref/Downsample.html}, note=[Accessed: 12-June-2026]}