CODEWITHSUNDEEP
rimageimage-processingcolorsraster
user2543622
user2543622

Reputation: 6796

crop image, convert to black and white and sharpen it

I want to take x, convert it into a black and white image. Then i want to convert all pixels that are below 100 to 0 and convert all pixels that are above 100 to 255. I want to get a sharper image where background will be white and objects within image will be black. And then store new x (black and white sharp image) on my hard drive. How could i do it?

library(raster)
r1 <- brick(system.file("external/rlogo.grd", package="raster"))
x <- crop(r1, extent(0,50,0,50))
plotRGB(x)

Based upon earlier question, i wrote below lines to convert r1 to black and white. But plotRGB function fails :(. Plot function works but it doesnt return me a black and white image

flat <- sum(x * c(0.2989, 0.5870, 0.1140))
plotRGB(flat)
flat
plot(flat)

========update1==========

in case anyone interested,

image colors can be swapped easily by using "1-twoclasses" in place of "twoclasses" in image and plot functions below

Upvotes: 1

Views: 3003

Answers (1)

Robert Hijmans
Robert Hijmans

Reputation: 47591

To actually see grays you need to provide these colors. 

library(raster)
r1 <- brick(system.file("external/rlogo.grd", package="raster"))
x <- crop(r1, extent(0,50,0,50))
flat <- sum(x * c(0.2989, 0.5870, 0.1140))
plot(flat, col=gray(seq(0,1,0.1)))

You can use the reclassify function to get values that are either 0 or 255 but in this case it would seem more sensible to use 1 and 2

twoclasses <- cut(flat, c(0,100,255))
plot(twoclasses, col=gray(c(0,1)))

To write to disk, you can do something like:

png(width=ncol(twoclasses)*10, height=nrow(twoclasses)*10)
par(mai=c(0,0,0,0))
image(twoclasses, col=gray(c(0,1)))
dev.off()

Upvotes: 2

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