Question

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 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

Assuming a correct result means having a valid pixel value i.e.

0<=pixel_value<=255

There can be multiple cases where the set will produce an incorrect result or an error:-

• The pixel value is negative
• one or both of the values (m1 and m2) could not be calculated because the parameters of getPixel(x,y) were out of bounds

Lets assume an image 4x4, where each cell contains the RGB values of that pixel

0,0,0	5,5,5	0,0,0	0,0,0
0,0,0	0,0,0	0,0,0	0,0,0
0,0,0	0,0,0	0,0,0	0,0,0
0,0,0	0,0,0	0,0,0	0,0,0

The Pairs which would produce wrong results would be:

Pair 1. (x,y)=(0,0)

(x,y)=[0,0,0]

(x+1,y)=[5,5,5]

Pair 2. (x,y)=(3,3)

(x,y)=[0,0,0]

(x+1,y)= //Out of bounds

Pair 3. (x,y)=(4,3)

(x,y)=//Out of bounds

(x+1,y)=//Out of bounds