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Graphics / sf::Image get every pixel around a pixel without crashing

« on: October 28, 2017, 03:26:42 pm »

I am currently trying to create a program that blurrs a given image. To do that I get the average rgb-values of all the pixels around one pixel, and then I set the pixel to this value.
The problem is, that if I am at a pixel that is at the border/edge of an image, the program will crash because it tries to get pixel information of pixels that are outside the image (eg. getPixel(-1, 0).

I could technically do dozens of if-statements, but I think it is no really elegant, fast or easy to maintain. Do you have any other suggestions? Currently I am only blurring every pixel except for the ones at the borders. But this looks a bit off, since it creates a non-fitting outline around the image.

If required, here is my code that blurrs an image:

void Framework::Blurr(unsigned level)
{
        unsigned counter = 0;

        while (counter < level)
        {
                for (int y = 1; y < orig.getSize().y - 1; y++)
                {
                        for (int x = 1; x < orig.getSize().x - 1; x++)
                        {
                                double r, g, b;
                               
                                r = (orig.getPixel(x-1, y-1).r + orig.getPixel(x, y-1).r + orig.getPixel(x+1, y-1).r +
                                        orig.getPixel(x, y-1).r + orig.getPixel(x+1, y).r +
                                        orig.getPixel(x-1, y+1).r + orig.getPixel(x, y+1).r + orig.getPixel(x+1, y+1).r) / 8;

                                g = (orig.getPixel(x-1, y-1).g + orig.getPixel(x, y-1).g + orig.getPixel(x+1, y-1).g +
                                        orig.getPixel(x, y-1).g + orig.getPixel(x+1, y).g +
                                        orig.getPixel(x-1, y+1).g + orig.getPixel(x, y+1).g + orig.getPixel(x+1, y+1).g) / 8;

                                b = (orig.getPixel(x-1, y-1).b + orig.getPixel(x, y-1).b + orig.getPixel(x+1, y-1).b +
                                        orig.getPixel(x, y-1).b + orig.getPixel(x+1, y).b +
                                        orig.getPixel(x-1, y+1).b + orig.getPixel(x, y+1).b + orig.getPixel(x+1, y+1).b) / 8;

                                post.setPixel(x, y, sf::Color(r, g, b));
                        }
                }
                orig = post;
                counter++;
        }


        text.loadFromImage(post);
        sprite.setTexture(text);
}