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".
- 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 generated 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 is specifically for a binary classification where the positive case is indicated with a cell value of 1 and the background or negative case is indicated with a cell value of 0. If an irregular shaped raster grid is provided, only chips and masks that contain no NA or NoDATA cells will be produced.
Three modes are available. If "All" is used, all image chips are generated even if they do not contain pixels mapped to the positive case. 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 have at least 1 pixel mapped to the positive class will be produced. Background- only chips will not be generated. 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" method is used, separate "positive" and "background" folders will be created with "images" and "masks" subfolders. Any chip that has at least 1 pixel mapped to the positive class will be written to the "positive" folder while any chip having only background pixels will be written to the "background" folder.