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NetEncoder: Encode inputs as tensors—Wolfram Documentation

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NetEncoder["name"]

represents an encoder that takes a given form of input and encodes it as an array for use in a net.

NetEncoder[{"name",…}]

represents an encoder with additional parameters specified.

Details
Details and Options Details and Options
Examples  
Basic Examples  
Scope  
Properties & Relations  
See Also
Tech Notes
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NetEncoder   

Listing of Net Encoders »

NetEncoder["name"]

represents an encoder that takes a given form of input and encodes it as an array for use in a net.

NetEncoder[{"name",…}]

represents an encoder with additional parameters specified.

Details

  • NetEncoder[…][input] gives the specified encoding for input.
  • NetEncoder[…][{input1,input2, …}] explicitly computes outputs for each of the inputi.
  • When given a NumericArray as input, the output will be a NumericArray.
  • Possible named encoders include:
  • "Audio"encode audio as a sequence of waveform amplitudes
    "AudioMelSpectrogram"encode audio as a mel spectrogram
    "AudioMFCC"encode audio as a sequence of MFCC vectors
    "AudioSpectrogram"encode audio as a spectrogram
    "AudioSTFT"encode audio as a sequence of Fourier transforms
    "Boolean"encode True and False as 1 and 0
    "Characters"encode characters in a string as a sequence of integer codes or one-hot vectors
    "Class"encode a class label as an integer code or a one-hot vector
    "FeatureExtractor"encode any kind of input as in FeatureExtraction
    "Function"use a custom function to encode an input
    "Image"encode a 2D image as a rank-3 array
    "Image3D"encode a 3D image as a rank-4 array
    "SubwordTokens"encode tokens in a string as a sequence of integer codes
    "Tokens"encode tokens in a string as a sequence of integer codes
    "UTF8"encode strings as their UTF8 bytes
    "VideoFrames"encode a video as a sequence of rank-3 arrays
  • A NetEncoder object can be attached to an input port of a net by specifying "port"->NetEncoder[…] when constructing the net. Specifying "port"->"name" will create an encoder using NetEncoder["name"] and attach it.
  • When NetTrain is allowed to automatically attach a loss layer and a NetDecoder is attached to the output of the net, a NetEncoder of the same type will be created for the "Target" input of the loss layer.
  • If the input to a NetEncoder is already in the correct form, the NetEncoder will be bypassed—that is, applying a NetEncoder twice has no effect.
  • NetEncoder[NetDecoder[…]] will create an encoder based on the parameters of an existing decoder.

Examples

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Basic Examples  (1)

Create a class encoder:

Wolfram Language code: enc = NetEncoder[{"Class", {"male", "female"}}]

Apply the encoder to an input:

Wolfram Language code: enc["female"]

The encoder maps across a batch of inputs:

Wolfram Language code: enc[{"male", "female", "female"}]

Scope  (1)

An encoder can be attached to the input port of a net. First, create an encoder:

Wolfram Language code: enc = NetEncoder["Image"]

Attach the encoder to the input of an ElementwiseLayer:

Wolfram Language code: layer = ElementwiseLayer[Sin, "Input" -> enc]

Apply the layer directly to an image:

Wolfram Language code: layer[[image]]

Properties & Relations  (3)

Attaching an encoder ensures that the sizes of all parameters and inputs can be inferred:

Wolfram Language code: net = NetInitialize@ LinearLayer[3, "Input" -> "Boolean"]
Wolfram Language code: net[True]
Wolfram Language code: NetInitialize@ LinearLayer[3]

A specific size of array can also be specified, without using an encoder:

Wolfram Language code: net = NetInitialize@LinearLayer[3, "Input" -> 1]

NetTrain will automatically try to attach an encoder when a net is not fully specified. Automatic attachment of a class encoder:

Wolfram Language code: net = NetTrain[NetChain[{UnitVectorLayer[], LinearLayer[]}], {"a" -> {1, 2}, "a" -> {2, 3}, "b" -> {3, 4}, "b" -> {4, 5}}]
Wolfram Language code: NetExtract[net, "Input"]

Automatic attachment of an image encoder:

Wolfram Language code: net = NetTrain[LinearLayer[], {[image] -> True, [image] -> False, [image] -> True, [image] -> False}]
Wolfram Language code: NetExtract[net, "Input"]
Wolfram Language code: net[[image]]

Applying a NetEncoder a second time is a no-op:

Wolfram Language code: enc = NetEncoder["Image"]
Wolfram Language code: enc[[image]]
Wolfram Language code: enc[enc[[image]]]
Wolfram Research (2016), NetEncoder, Wolfram Language function, https://reference.wolfram.com/language/ref/NetEncoder.html (updated 2022).

Text

Wolfram Research (2016), NetEncoder, Wolfram Language function, https://reference.wolfram.com/language/ref/NetEncoder.html (updated 2022).

CMS

Wolfram Language. 2016. "NetEncoder." Wolfram Language & System Documentation Center. Wolfram Research. Last Modified 2022. https://reference.wolfram.com/language/ref/NetEncoder.html.

APA

Wolfram Language. (2016). NetEncoder. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/NetEncoder.html

BibTeX

@misc{reference.wolfram_2026_netencoder, author="Wolfram Research", title="{NetEncoder}", year="2022", howpublished="\url{https://reference.wolfram.com/language/ref/NetEncoder.html}", note=[Accessed: 14-November-2026]}

BibLaTeX

@online{reference.wolfram_2026_netencoder, organization={Wolfram Research}, title={NetEncoder}, year={2022}, url={https://reference.wolfram.com/language/ref/NetEncoder.html}, note=[Accessed: 14-November-2026]}