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extractPixels: Machine Learning Extract Pixel Data Transform

  • Article

Extracts the pixel values from an image.

Usage

  extractPixels(vars, useAlpha = FALSE, useRed = TRUE, useGreen = TRUE,
    useBlue = TRUE, interleaveARGB = FALSE, convert = TRUE, offset = NULL,
    scale = NULL)

Arguments

vars

A named list of character vectors of input variable names and the name of the output variable. Note that the input variables must be of the same type. For one-to-one mappings between input and output variables, a named character vector can be used.

useAlpha

Specifies whether to use alpha channel. The default value is FALSE.

useRed

Specifies whether to use red channel. The default value is TRUE.

useGreen

Specifies whether to use green channel. The default value is TRUE.

useBlue

Specifies whether to use blue channel. The default value is TRUE.

interleaveARGB

Whether to separate each channel or interleave in ARGB order. This might be important, for example, if you are training a convolutional neural network, since this would affect the shape of the kernel, stride etc.

convert

Whether to convert to floating point. The default value is FALSE.

offset

Specifies the offset (pre-scale). This requires convert = TRUE. The default value is NULL.

scale

Specifies the scale factor. This requires convert = TRUE. The default value is NULL.

Details

extractPixels extracts the pixel values from an image. The input variables are images of the same size, typically the output of a resizeImage transform. The output is pixel data in vector form that are typically used as features for a learner.

Value

A maml object defining the transform.

Author(s)

Microsoft Corporation Microsoft Technical Support

Examples


 train <- data.frame(Path = c(system.file("help/figures/RevolutionAnalyticslogo.png", package = "MicrosoftML")), Label = c(TRUE), stringsAsFactors = FALSE)

 # Loads the images from variable Path, resizes the images to 1x1 pixels and trains a neural net.
 model <- rxNeuralNet(
     Label ~ Features,
     data = train,
     mlTransforms = list(
         loadImage(vars = list(Features = "Path")),
         resizeImage(vars = "Features", width = 1, height = 1, resizing = "Aniso"),
         extractPixels(vars = "Features")
         ),
     mlTransformVars = "Path",
     numHiddenNodes = 1,
     numIterations = 1)

 # Featurizes the images from variable Path using the default model, and trains a linear model on the result.
 model <- rxFastLinear(
     Label ~ Features,
     data = train,
     mlTransforms = list(
         loadImage(vars = list(Features = "Path")),
         resizeImage(vars = "Features", width = 224, height = 224), # If dnnModel == "AlexNet", the image has to be resized to 227x227.
         extractPixels(vars = "Features"),
         featurizeImage(var = "Features")
         ),
     mlTransformVars = "Path")