CODEWITHSUNDEEP
rimage-processing
EugeneAliev93
EugeneAliev93

Reputation: 3

Return coordinates of pixels with a given RGB/HEX value

Let's say I have an image like this smiley face below:

Just as an example, a white background with a blue smile drawn on it

I would like to write an R script that returns the pixel coordinates of the pixels that are blue. Ideally I'd want to specify the RGB/HEX/etc value of the blue when using this package/function, rather than using a threshold or a logic calculation where I'm looking at whether or not a pixel is 'white or not white'. I know there are tools and packages in Python and MATLAB but I was wondering if there was a suitable package in R I could use instead. Thanks!

Upvotes: 0

Views: 197

Answers (1)

Allan Cameron
Allan Cameron

Reputation: 174478

You can load the PNG as a 3d array (n_rows x n_columns x (R, G, B, alpha)) using the png package. Then you can do something like this:

find_pixels <- function(png_path, string)
{
  img <- 255 * png::readPNG(png_path)
  R <- as.numeric(paste0("0x", substr(string, 2, 3)))
  G <- as.numeric(paste0("0x", substr(string, 4, 5)))
  B <- as.numeric(paste0("0x", substr(string, 6, 7)))
  which(img[,,1] == R & img[,,2] == B & img[,,3] == G, arr.ind = TRUE)
}

find_pixels("~/smiley.png", "#FAFAFA")
#>      row col
#> [1,]   1   1
#> [2,]   2   1
#> [3,]   3   1
#> [4,]   4   1
#> [5,]   5   1
#> [6,]   6   1
#> ... etc

Upvotes: 1

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