So called 'defines' are properties that are passed along to external filters and libraries. Usually defines are used in image_read or image_write to control the image encoder/decoder, but you can also set these manually on the image object.

image_set_defines(image, defines)

Arguments

image

magick image object returned by image_read() or image_graph()

defines

a named character vector with extra options to control reading. These are the -define key{=value} settings in the command line tool. Use an empty string for value-less defines, and NA to unset a define.

Details

The defines values must be a character string, where the names contain the defines keys. Each name must be of the format "enc:key" where the first part is the encoder or filter to which the key is passed. For example "png:...." defines can control the encoding and decoding of png images.

The image_set_defines function does not make a copy of the image, so the defined values remain in the image object until they are overwritten or unset.

See also

Examples

# Write an image x <- image_read("https://jeroen.github.io/images/frink.png") image_write(x, "frink.png") # Pass some properties to PNG encoder defines <- c("png:compression-filter" = "1", "png:compression-level" = "0") image_set_defines(x, defines) image_write(x, "frink-uncompressed.png") # Unset properties defines[1:2] = NA image_set_defines(x, defines) image_write(x, "frink-final.png") # Compare size and cleanup file.info(c("frink.png", "frink-uncompressed.png", "frink-final.png"))
#> size isdir mode mtime #> frink.png 67143 FALSE 666 2021-05-01 22:27:22 #> frink-uncompressed.png 392512 FALSE 666 2021-05-01 22:27:22 #> frink-final.png 67143 FALSE 666 2021-05-01 22:27:22 #> ctime atime uid gid uname #> frink.png 2021-05-01 22:27:22 2021-05-01 22:27:22 0 0 root #> frink-uncompressed.png 2021-05-01 22:27:22 2021-05-01 22:27:22 0 0 root #> frink-final.png 2021-05-01 22:27:22 2021-05-01 22:27:22 0 0 root #> grname #> frink.png root #> frink-uncompressed.png root #> frink-final.png root
unlink(c("frink.png", "frink-uncompressed.png", "frink-final.png"))