Binarize Image in Android

Question

I am developing android app that uses tesseract OCR to scan a text from image,
I heard that binarizing image before performing OCR on it will give better result,
So

Answer 1

I had a similar project involving colors, although on another platform.

Although they might be other better algorithms, I used a function (GetColorDistance) to calculate the distances between two colors, in the 3D RGB space, by using the Pythagorean theorem. GetNewColor calculates whether the a color is closer to white or black, and then returns a black or white accordingly. Finally, the GetBitmapBinary function processes the pixels on the bitmap and converts them into black & white.

private Bitmap GetBinaryBitmap(Bitmap bitmap_src)
    {
        Bitmap bitmap_new=bitmap_src.copy(bitmap_src.getConfig(), true);



    for(int x=0; x<bitmap_new.getWidth(); x++)
    {
        for(int y=0; y<bitmap_new.getHeight(); y++)
        {
            int color=bitmap_new.getPixel(x, y);
            color=GetNewColor(color);
            bitmap_new.setPixel(x, y, color);
        }
    }

    return bitmap_new;
}


private double GetColorDistance(int c1, int c2)
{
    int db=Color.blue(c1)-Color.blue(c2);
    int dg=Color.green(c1)-Color.green(c2);
    int dr=Color.red(c1)-Color.red(c2);


    double d=Math.sqrt(  Math.pow(db, 2) + Math.pow(dg, 2) +Math.pow(dr, 2)  );
    return d;
}

private int GetNewColor(int c)
{
    double dwhite=GetColorDistance(c,Color.WHITE);
    double dblack=GetColorDistance(c,Color.BLACK);

    if(dwhite<=dblack)
    {
        return Color.WHITE;

    }
    else
    {
        return Color.BLACK;
    }


}

You can modify the GetNewColor function for better results in different light densities. For example, you may multiply dblack by 1.5 so that darker pixels can become white, in a dark environment.