Determine file image size in R
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jpeg_dimensions <- function(filename, bytes = 1024) { | |
bytes <- readBin(filename, "raw", n = bytes) | |
if (length(bytes) < 2 || bytes[[1]] != 0xFF || bytes[[2]] != 0xD8) { | |
stop("Couldn't decode jpeg") | |
} | |
ff <- which(bytes == 0xFF) | |
c0 <- which(bytes == 0xC0) | |
sof0 <- head(ff[ff %in% (c0 - 1)], 1) | |
if (length(sof0) == 0) { | |
stop("Couldn't decode jpeg") | |
} | |
if (length(bytes) < sof0 + 9) { | |
stop("Couldn't decode jpeg") | |
} | |
height_bytes <- bytes[(sof0 + 5):(sof0 + 6)] | |
width_bytes <- bytes[(sof0 + 7):(sof0 + 8)] | |
list( | |
width = readBin(width_bytes, "integer", 1, 2, endian = "big"), | |
height = readBin(height_bytes, "integer", 1, 2, endian = "big") | |
) | |
} | |
png_dimensions <- function(filename) { | |
bytes <- readBin(filename, "raw", n = 24) | |
if (length(bytes) < 24) { | |
stop("Couldn't decode png") | |
} | |
png_signature <- as.raw(c(0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A)) | |
if (!identical(bytes[1:8], png_signature)) { | |
stop("Couldn't decode png") | |
} | |
if (!identical(bytes[13:16], charToRaw("IHDR"))) { | |
stop("Couldn't decode png") | |
} | |
width_bytes <- bytes[17:20] | |
height_bytes <- bytes[21:24] | |
list( | |
width = readBin(width_bytes, "integer", 1, 4, endian = "big"), | |
height = readBin(height_bytes, "integer", 1, 4, endian = "big") | |
) | |
} | |
gif_dimensions <- function(filename) { | |
bytes <- readBin(filename, "raw", n = 10) | |
if (length(bytes) < 10) { | |
stop("Couldn't decode gif") | |
} | |
if (!identical(bytes[1:6], charToRaw("GIF89a")) && !identical(bytes[1:6], charToRaw("GIF87a"))) { | |
stop("Couldn't decode gif") | |
} | |
width_bytes <- bytes[7:8] | |
height_bytes <- bytes[9:10] | |
list( | |
width = readBin(width_bytes, "integer", 1, 2, endian = "little"), | |
height = readBin(height_bytes, "integer", 1, 2, endian = "little") | |
) | |
} |
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