Question

JavaScript, Consider the following code fragment, that is supposed to compute the pixel value

let c = image.getPixel(x, y);
const m1 = (c[0] + c[1] + c[2]) / 3;
c = image.getPixel(x + 1, y);
const m2 = (c[0] + c[1] + c[2]) / 3;
image.setPixel(x, y, [m1 - m2, m1 - m2, m1 - m2]);

Give three pairs of pixel values (x, y) = [?, ?, ?] and (x+1, y) = [?, ?, ?] in the input image, for which this code does not produce the correct result.

Pair 1.)

(x, y) =

(x+1, y) =

Pair 2.)

(x, y) =

(x+1, y)=

Pair 3.)

(x, y) =

(x+1, y)=

Answer 1

In this code, the RGB index of pixel (x,y) is set to the the average RGB of (x,y) - (x+1, y)

Also, we know that each colour index is a 8 bits value between 0 to 255 in decimals.

So, any value out of this range will produce error, such as:

Pair 1 :

(x, y) = [ 51, 51, 51] and (x+1, y) = [255, 255, 255]

Hence, m1 - m2 = 51 - 255 = -201 ( not acceptable)

Pair 2 :

(X,y) = [21, 43, 56] and (x+1,y) = [255, 124, 200]

M1 - m2 = 40 - 193 = - 153 (not acceptable)

Pair 3:

(x,y) = [0, 0, 0] and (X+1, y) = [ 51,51,51]

m1 - m2 = 0 - 51 = -51 ( not acceptable)