image prcoessing

Programming Questions

aizen92

in Programming Questions • 2 years ago

Hello,

I wrote a code that is supposed to apply the Floyd–Steinberg dithering on an image, but i keep getting an error, can someone plz check my code, and tell me where im wrong at.

Thanks in advance

the code is here:

PImage img;
void setup ()
{
size (300, 300);
img = loadImage("baboon.gif");
img.resize(255, 255);
}
void draw ()
{
background (255);
toGrayscale();
display(10, 10);
}
void toGrayscale ()
{
img.loadPixels();
for (int i = 0; i < img.pixels.length; i++)
{
float r = 0.30 * red(img.pixels[i]);
float g = 0.59 * green(img.pixels[i]);
float b = 0.11 * blue(img.pixels[i]);
img.pixels[i] = color (r + g + b);
}
img.updatePixels();
}
void display (float x, float y)
{
float e;
img.loadPixels();
for (int i = 0; i < img.height; i++)
{
for (int j = 0; j < img.width; j++)
{
int loc = i + (j * img.width);
float t = red(img.pixels[loc]);
if (t < 127)
{
e = t - 0;
img.pixels[loc] = color (0);
}else{
e = t - 255;
img.pixels[loc] = color (255);
}
int p1 = i + ((j + 1) * img.width);
int p2 = (i + 1) + ((j - 1) * img.width);
int p3 = (i + 1) + (j * img.width);
int p4 = (i + 1) + ((j + 1) * img.width);
float p1C = red(img.pixels[p1]);
float p2C = red(img.pixels[p2]); // array of the pixels is giving error out of bounds
float p3C = red(img.pixels[p3]);
float p4C = red(img.pixels[p4]);
if ((p1C + (e * (7.0 / 16.0))) <= 0)
{
img.pixels[p1] = color (0);
}else if ((p1C + (e * (7.0 / 16.0))) >= 255) {
img.pixels[p1] = color (255);
}
if ((p2C + (e * (3.0 / 16.0))) <= 0)
{
img.pixels[p2] = color (0);
}else if ((p2C + (e * (3.0 / 16.0))) >= 255) {
img.pixels[p2] = color (255);
}
if ((p3C + (e * (5.0 / 16.0))) <= 0)
{
img.pixels[p3] = color (0);
}else if ((p3C + (e * (5.0 / 16.0))) >= 255) {
img.pixels[p3] = color (255);
}
if ((p4C + (e * (1.0 / 16.0))) <= 0)
{
img.pixels[p4] = color (0);
}else if ((p4C + (e * (1.0 / 16.0))) >= 255) {
img.pixels[p4] = color (255);
}
}
}
img.updatePixels();
image(img, x, y);
}

Replies(7)

PhiLho

Re: image prcoessing

2 years ago

I just added a line after the computation of p2:
println(i + " " + j + " " + p2);
Got 0, 0, and a negative value... Revise your algorithm.

aizen92

yeh, its still in the first loop of both for loops, i guess its because the upper middle pixel of the mask must be the first one at the beginning and theirs nothing to its left, so i guess its causing out of bounds, or am i wrong?

PhiLho

Re: image prcoessing

2 years ago

No, your analysis is fine. Perhaps start at indices of 1.

aizen92

Re: image prcoessing

2 years ago

ok, i started the indices at 1, it got past the error of p2, but it got stuck on p1C.

I re-wrote the code in a smaller one i guess, and i got this one

PImage img;
void setup ()
{
size (300, 300);
img = loadImage("baboon.gif");
img.resize(255, 255);
}
void draw ()
{
background (255);
toGrayscale();
display(10, 10);
}
void toGrayscale ()
{
img.loadPixels();
for (int i = 0; i < img.pixels.length; i++)
{
float r = 0.30 * red(img.pixels[i]);
float g = 0.59 * green(img.pixels[i]);
float b = 0.11 * blue(img.pixels[i]);
img.pixels[i] = color (r + g + b);
}
img.updatePixels();
}
void display (float x, float y)
{
float oldPixel;
float newPixel;
float error;
img.loadPixels();
for (int j = 1; j < img.height; j++)
{
for (int i = 1; i < img.width; i++)
{
int loc = i + (j * img.width);
oldPixel = red(img.pixels[loc]);
if (oldPixel < 127)
{
newPixel = 0;
}else{
newPixel = 255;
}
img.pixels[loc] = color (newPixel);
error = oldPixel - newPixel;
img.pixels[(i + 1) + (j * img.width)] += color((7.0/16.0) * error);
img.pixels[(i - 1) + ((j + 1) * img.width)] += color((3.0/16.0) * error);
img.pixels[i + ((j + 1) * img.width)] += color((5.0/16.0) * error);
img.pixels[(i + 1) + ((j + 1) * img.width)] += color((1.0/16.0) * error);
}
}
img.updatePixels();
image (img, x, y);
}

, now i tried this one, i got an error of out of bounds at line 64.

if i change the indices if the loops can it work, or it doesnt matter?

PhiLho

Re: image prcoessing

2 years ago

" if i change the indices if the loops can it work, or it doesnt matter?"
Why don't you just try?

Note: you might need also to iterate unlike img.width-1 / img.height-1, ie. to take also in account the opposite margins.

aizen92

Re: image prcoessing

2 years ago

well, i put bth loops to end at width - 1 and height - 1, and it worked

thnx phi.lho for the help

aizen92

Re: image prcoessing

2 years ago

now that i see it, im comparing it to a threshold picture it seems to be the same but the inverse of it... i dont know if it is wrong or wite

The first one is using the threshold dithering, and the last one from the code i did, it is normal or what?

EDIT: i used another code for the error diffuse and got this image

or is this a better one?

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