Convert negative image to positive [closed]

Question

I have old negative films I have scanned onto my computer. I want to write a small program to convert the negative Images to its positive state.

I know there are several image editor applications out there which I can use to achieve this conversion, but I am researching on how to manipulate the pixels to convert them myself via a small app.

Can anyone give me a head start on this? Sample code if possible will also be much appreciated.

Answer 1

I just wrote up a working example. Given the following input image img.png.

The output will be a new image invert-img.png like

import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;

class Convert
{
    public static void main(String[] args)
    {
        invertImage("img.png");
    }

    public static void invertImage(String imageName) {
        BufferedImage inputFile = null;
        try {
            inputFile = ImageIO.read(new File(imageName));
        } catch (IOException e) {
            e.printStackTrace();
        }

        for (int x = 0; x < inputFile.getWidth(); x++) {
            for (int y = 0; y < inputFile.getHeight(); y++) {
                int rgba = inputFile.getRGB(x, y);
                Color col = new Color(rgba, true);
                col = new Color(255 - col.getRed(),
                                255 - col.getGreen(),
                                255 - col.getBlue());
                inputFile.setRGB(x, y, col.getRGB());
            }
        }

        try {
            File outputFile = new File("invert-"+imageName);
            ImageIO.write(inputFile, "png", outputFile);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

If you want to create a monochrome image, you can alter the calculation of col to something like this:

int MONO_THRESHOLD = 368;
if (col.getRed() + col.getGreen() + col.getBlue() > MONO_THRESHOLD)
    col = new Color(255, 255, 255);
else
    col = new Color(0, 0, 0);

The above will give you the following image

You can adjust MONO_THRESHOLD to get a more pleasing output. Increasing the number will make the pixel darker and vice versa.