resizeImages {imageseg}

Resize and save images

Description

Resize and save images

Usage

resizeImages(
  imageDir,
  fileNames,
  pattern,
  patternInclude = TRUE,
  type,
  dimensions,
  validRegion,
  preserveAspect = TRUE,
  filter = NULL,
  colorspace,
  binary,
  gravity = "Center",
  imageFormats = c("JPG|TIF|PNG|JPEG|TIFF"),
  outDir,
  cores = 1,
  compression = "Lossless"
)

Arguments

imageDir

Character. Directory containing raw images

fileNames

character. File names to load (they will still be filtered by pattern, if defined)

pattern

character. Pattern to search in file names

patternInclude

logical. Include images with pattern in file names (TRUE) or exclude (FALSE)

type

character. "canopy" or "understory". Will set image dimensions accordingly to predefined c(256, 256) or c(160, 256), respectively (optional). Alternatively, use dimensions.

dimensions

integer. image dimensions provides as c(width, height) in pixels. If specified, overrides type

validRegion

character. If defined, use string as argument geometry in image_crop (output of geometry_area), which will crop all images to the same region before resizing (optional). If undefined, don't crop.

preserveAspect

logical. If TRUE, images will be cropped to aspect ratio of output before resizing (thus preserving original aspect ratio, but losing parts of the image). If FALSE, images will be simply resized from their input size to the desired output (not preserving aspect ratio).

filter

character. Resampling filter. Passed to argument filter in image_resize. See magick::filter_types() for available options. Default is LanczosFilter.

colorspace

character. If defined, image will be converted to the requested colorspace. If undefined, colorspace will remain unchanged. Must be a valid argument to magick::colorspace_types(). In practice, only "sRGB" and "Gray" will be relevant.

binary

logical. If colorspace is "Gray", make the output binary?

gravity

if preserveAspect = TRUE and images need to be cropped, the gravity argument to use in image_crop.

imageFormats

character. Image file formats to read.

outDir

character. Directory to save resized images in.

cores

integer. Number of cores to use for parallel processing

compression

character. Compression type to use in image_write. See compress_types. By default, "Lossless" for grayscale images, "Undefined" for color images.

Details

Resizing is done by image_resize and will ensure that the resized images have exactly the desired dimensions.

If preserveAspect = TRUE, input images will first be cropped to the maximum area with the aspect ratio of the desired output (1:1 (square) for type = "canopy", 5:8 for type = "understory"), by default in the center of the input image (argument gravity). This will usually lead to the loss of parts of the image, but the remaining part of the image is not deformed compared to the original. Alternatively, if preserveAspect = FALSE, input images will be resized to the requested dimensions without cropping (thus no loss of part of the image), but the aspect ratio changes. If aspect ratio changes too strongly it may negatively affect model performance.

Resizing is done using "!" in the geometry syntax. See geometry for details.

compression = "Lossless" is used to ensure no compression artefacts in saved images (which would for example introduce grayscale values in black/white images). If small file sizes are important, you can change it to save compressed images.

Value

No R output, only resized images are saved on disk

Examples

# Example 1: Canopy
wd_can <- system.file("images/canopy/raw",
                      package = "imageseg")

wd_out_can <- file.path(tempdir(), "canopy", "resized")
resizeImages(imageDir = wd_can,
             type = "canopy",
             outDir = wd_out_can)

filename_resized <- list.files(wd_out_can, full.names = TRUE)

# check output
img_can <- magick::image_read(filename_resized)
img_can

# Example 2: Understory
wd_us <- system.file("images/understory/raw",
                      package = "imageseg")
wd_out_us <- file.path(tempdir(), "understory", "resized")

# note, these are png images
resizeImages(imageDir = wd_us,
             type = "understory",
             outDir = wd_out_us)

filename_resized <- list.files(wd_out_us, full.names = TRUE)

# check output
img_us <- magick::image_read(filename_resized)
img_us