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I have an image from a satellite with pixels values between 0 and 255. This image contains several tests of information No/Yes (0/1) storage in a 48-bit product. I need to get the information for a test in a pixel; specifically, I need to get the information of the bit (19).

I may assume that for a pixel of value = 0 the information for all the tests is gone be No (0); however, this is not the case for pixels with values greater than 0. I can extract the pixel value, but how I can extract the bit field information from a pixel in R?

Surely you have seen something similar, could you guide me to do this in R?

I used intToBits(), but this return just 32 bits and I am not sure if this is the correct answer.

J. Antonio Guzmán Q.
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1 Answers1

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This question may be useful: How to convert integer number into binary vector?

your_pixels <- c(0,1,100,255)
your_bits <- sapply(your_pixels, function(x) as.integer(intToBits(x)))
your_bits

      [,1] [,2] [,3] [,4]
 [1,]    0    1    0    1
 [2,]    0    0    0    1
 [3,]    0    0    1    1
 [4,]    0    0    0    1
 [5,]    0    0    0    1
 [6,]    0    0    1    1
 [7,]    0    0    1    1
 [8,]    0    0    0    1
 [9,]    0    0    0    0
[10,]    0    0    0    0
[11,]    0    0    0    0
[12,]    0    0    0    0
[13,]    0    0    0    0
[14,]    0    0    0    0
[15,]    0    0    0    0
[16,]    0    0    0    0
[17,]    0    0    0    0
[18,]    0    0    0    0
[19,]    0    0    0    0        # notice, no data here
[20,]    0    0    0    0
[21,]    0    0    0    0
[22,]    0    0    0    0
[23,]    0    0    0    0
[24,]    0    0    0    0
[25,]    0    0    0    0
[26,]    0    0    0    0
[27,]    0    0    0    0
[28,]    0    0    0    0
[29,]    0    0    0    0
[30,]    0    0    0    0
[31,]    0    0    0    0
[32,]    0    0    0    0

Then to get the value for your test #19, use your_bits[19,] (unless you're counting 19 from the beginning of the number, in which case your_bits[14,]). However, you will notice that the 19th bit for the entire range 0:255 will be 0. The highest bit used in the number 255 is the 8th bit.

The most common image encoding is usually RGBA, which is 32 bits per pixel (0:255 for each channel, red/blue/green/alpha). You mentioned your image has 48 bits per pixel. Integers in R are limited to 32 bits (and intToBits only works on integers), so some detail about how you're reading the pixels into values would be necessary to help you.

There are packages to return the binary representation of large numbers, like bit64: https://cran.r-project.org/web/packages/bit64/index.html

library(bit64)
your_pixels48 <- c(0, 1, 100, 255, 2^48-1)

[1] 0.00000e+00 1.00000e+00 1.00000e+02 2.55000e+02 2.81475e+14



your_pixels48 <- as.integer64(your_pixels48)

integer64
[1] 0               1               100             255             281474976710655



your_bits48 <- as.bitstring(your_pixels48)

[1] "0000000000000000000000000000000000000000000000000000000000000000"
[2] "0000000000000000000000000000000000000000000000000000000000000001"
[3] "0000000000000000000000000000000000000000000000000000000001100100"
[4] "0000000000000000000000000000000000000000000000000000000011111111"
[5] "0000000000000000111111111111111111111111111111111111111111111111"

However, note that this returns a string of the binary representation. In that case you can use string operations to access the 19th slot:

substr(your_bits48, start = 19, stop = 19)

[1] "0" "0" "0" "0" "1"

Which you then need to coerce to a number again with as.numeric or as.integer. However, this is counting from the beginning of the number, not the end, so you really need to start= and stop= at (64:1)[19] or 46.

Presumably you want more data than just the 19th value, so you can also use strsplit(your_bits48, "") to split the bitstring into every value, which can then be indexed in whatever way you want.

Brian
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