write_png: Write PNG

In fastpng: Read and Write PNG Files with Configurable Decoder/Encoder Options

Write PNG

Description

Write PNG

Usage

write_png(
  image,
  file = NULL,
  palette = NULL,
  use_filter = TRUE,
  compression_level = -1L,
  avoid_transpose = FALSE,
  bits = 8,
  trns = NULL,
  raw_spec = NULL
)

Arguments

image	image. Supported image types: Numeric arrays Numeric arrays with values in the range [0, 1], with 1, 2, 3 or 4 colour planes to represent gray, gray+alpha, rgb and rgba pixels, respectively Rasters Rasters with a mixture of named colours (e.g. 'red'), and hex colours of the form #RGB, #RGBA, #RRGGBB and #RRGGBBAA Integer arrays Integer arrays with values in [0,255] treated as 8-bit image data. Integer arrays with values in [0, 65535] treated as 16-bit image data Native rasters Integer matrices containing colurs in native format i.e. 8-bit RGBA values packed into a single integer Integer matrix + an indexed palette of colors Can be saved as an indexed PNG Raw vectors Vectors of raw bytes must be accompanied by a raw_spec which details how the bytes are to be interpreted e.g. colour depth, width and height
file	If NULL (the default) then return PNG data as raw vector, otherwise write to the given file path.
palette	character vector of up to 256 colors. If specified, and the image is a 2D matrix of integer or numeric values, then an indexed PNG is written where the matrix values indicate the colour palette value to use. The values in the matrix must range from 0 (for the first colour)
use_filter	Use PNG filtering to help reduce size? Default: TRUE. If FALSE, then filtering will be disabled which can make image writing faster.
compression_level	compression level for PNG. Default: -1 means to use the default compression level. Other valid values are in range [0, 9]. In general, lower compression levels result in faster compression, but larger image sizes. For fastest image writing, set compression_level to 0 to completely disable compression.
avoid_transpose	Should transposition be avoided if possible so as to maximise the speed of writing the PNG? Default: FALSE. PNG is a row-major image format, but R stores data in column-major ordering. When writing data to PNG, it is often necessary to transpose the R data to match what PNG requires. If this option is set to TRUE then the image is written without this transposition and should speed up PNG creation. This option only has an effect for 2D integer and numeric matrix formats.
bits	bit depth. default 8. Valid values are 8 and 16. This option only has an effect when image to output is a numeric array.
trns	color to be treated as transparent in RGB and Greyscale images - without specifying a full alpha channel. Only a single color can be specified and it will be treated as a fully transparent color in the image. This setting is only used when writing RGB and Greyscale images. For 8-bit RGB images, the value may be a hex color value i.e. "#RRGGBB" or a vector of 3 numeric values in the range [0, 255]. For 8-bit greyscale images, must be a single integer value in the range [0, 255]. For 16-bit RGB images, the value may be a vector of 3 numeric values in the range [0, 65535]. For 16-bit greyscale images, must be a single integer value in the range [0, 65535]. Default: NULL - means to not add a transparency color.
raw_spec	named list of image specifications for encoding a raw vector to PNG. Use raw_spec() to create such a list in the correct format. This argument is only required if the image argument is a raw vector.

Value

If file argument provided, function writes to file and returns nothing, otherwise it returns a raw vector holding the PNG encoded data.

Examples

# create a small greyscale integer matrix, and write it to a PNG file
mat <- matrix(c(0L, 255L), 3, 4)
pngfile <- tempfile()
write_png(mat, file = pngfile)
im <- read_png(pngfile, type = 'raster') 
plot(im, interpolate = FALSE)

fastpng documentation built on April 3, 2025, 10:01 p.m.