Denoise a PNG Image

DenoisePNG.R

library(png)
library(abind)
library(impute)

SplitImage <- function(rgb.array) {
    # decompose image into RGB elements
    rgb.list <- list()
    for (i in 1:dim(rgb.array)[3]) {
        rgb.list[[i]] <- rgb.array[, , i]
    }
    return(rgb.list)
}

DenoisePNG <- function(png.file, k=10, display.only=TRUE) {
    # denoise PNG image
    rgb.array <- readPNG(png.file)
    rgb.list <- SplitImage(rgb.array)
    
    ZerosToNA <- function(mat) {
        mat[mat == 0] <- NA
        return(mat)
    }
    # change zero value pixels to NA
    # impute NA values using kNN
    rgb.list <- lapply(rgb.list, ZerosToNA)
    rgb.imputed <- lapply(rgb.list, function(mat) {
        imputed <- impute.knn(mat, k=k)
        return(imputed$data)
    })
    # restore original dimensions
    denoised.img <- abind(rgb.imputed, along=3)
    
    filename <- sprintf("denoised_k%s_%s", k, png.file)
    writePNG(denoised.img, filename)
    grid.raster(readPNG(filename, native=TRUE))
    if (display.only){
        file.remove(filename)
    }
}