Generate image chips from images and associated raster masks
Usage
makeChips(
image,
mask,
n_channels = 3,
size = 256,
stride_x = 256,
stride_y = 256,
outDir,
mode = "All",
useExistingDir = FALSE
)Arguments
- image
SpatRaster object or path to input image. Function will generate a SpatRaster object internally. The image and mask must have the same extent, number of rows and columns of pixels, cell size, and coordinate reference system.
- mask
SpatRaster object or path to single-band mask. Function will generate a SpatRaster object internally. The image and mask must have the same extent, number of rows and columns of pixels, cell size, and coordinate reference system.
- n_channels
Number of channels in the input image. Default is 3.
- size
Size of image chips as number of rows and columns of pixels. Default is 256.
- stride_x
Stride in the x (columns) direction. Default is 256.
- stride_y
Stride in the y (rows) direction. Default is 256.
- outDir
Full or relative path to the current working directory where you want to write the chips to. Subfolders in this directory will be generated by the function if useExistingDir = FALSE. You must include the final forward slash in the file path (e.g., "C:/data/chips/").
- mode
Either "All", "Positive", or "Divided". Please see the explanations provided above. The default is "All". For multiclass problems, "All" or "Positive" are recommended.
- useExistingDir
TRUE or FALSE. Write chips into an existing directory with subfolders already defined as opposed to using a new directory. This can be used if you want to add chips to an existing set of chips. However, the "mode" should be the same as that used to generate the original chips. Default is FALSE.
Details
This function generates image and mask chips from an input image and associated raster mask. The chips are written into the defined directory. The number of rows and columns of pixels in each chip are equal to the size argument. If a stride_x and/or stride_y is used that is different from the size argument, resulting chips will either overlap or have gaps between them. In order to not have overlap or gaps, the stride_x and stride_y arguments should be the same as the size argument. Both the image chips and associated masks are written to TIFF format (".tif"). Input data are not limited to three band images. This function supports both binary and multiclass classification problems. For binary classification the background class should be coded 0 and the positive class coded 1. For multiclass problems, class codes should be sequential integers (e.g., 0 to n-1 or 1 to n). In all modes, chips or masks that contain any NA or NoData cells are excluded.
Three modes are available. If "All" is used, all image chips are generated, including those that contain only background pixels (class code 0). Within the provided directory, image chips will be written to an "images" folder and masks will be written to a "masks" folder. If "Positive" is used, only chips that contain at least one non-background pixel (i.e., any pixel with a class code greater than 0) will be produced. This mode is recommended for both binary and multiclass problems where background-only chips should be excluded. Within the provided directory, image chips will be written to an "images" folder and masks will be written to a "masks" folder. Lastly, if the "Divided" mode is used, separate "positive" and "background" folders will be created with "images" and "masks" subfolders. Any chip containing at least one non-background pixel will be written to the "positive" folder; chips containing only background pixels will be written to the "background" folder. This mode is primarily intended for binary classification problems.
Examples
if (FALSE) { # \dontrun{
# Binary classification
makeChips(image = "INPUT IMAGE FILE NAME AND PATH",
mask = "INPUT RASTER MASK FILE NAME AND PATH",
n_channels = 3,
size = 256,
stride_x = 256,
stride_y = 256,
outDir = "OUTPUT DIRECTORY IN WHICH TO SAVE CHIPS",
mode = "Positive",
useExistingDir = FALSE)
# Multiclass classification
makeChips(image = "INPUT IMAGE FILE NAME AND PATH",
mask = "INPUT RASTER MASK FILE NAME AND PATH",
n_channels = 3,
size = 256,
stride_x = 256,
stride_y = 256,
outDir = "OUTPUT DIRECTORY IN WHICH TO SAVE CHIPS",
mode = "Positive",
useExistingDir = FALSE)
} # }