[image-processing] image processing to improve tesseract OCR accuracy

Java version for Sathyaraj's code above:

// Resize
public Bitmap resize(Bitmap img, int newWidth, int newHeight) {
    Bitmap bmap = img.copy(img.getConfig(), true);

    double nWidthFactor = (double) img.getWidth() / (double) newWidth;
    double nHeightFactor = (double) img.getHeight() / (double) newHeight;

    double fx, fy, nx, ny;
    int cx, cy, fr_x, fr_y;
    int color1;
    int color2;
    int color3;
    int color4;
    byte nRed, nGreen, nBlue;

    byte bp1, bp2;

    for (int x = 0; x < bmap.getWidth(); ++x) {
        for (int y = 0; y < bmap.getHeight(); ++y) {

            fr_x = (int) Math.floor(x * nWidthFactor);
            fr_y = (int) Math.floor(y * nHeightFactor);
            cx = fr_x + 1;
            if (cx >= img.getWidth())
                cx = fr_x;
            cy = fr_y + 1;
            if (cy >= img.getHeight())
                cy = fr_y;
            fx = x * nWidthFactor - fr_x;
            fy = y * nHeightFactor - fr_y;
            nx = 1.0 - fx;
            ny = 1.0 - fy;

            color1 = img.getPixel(fr_x, fr_y);
            color2 = img.getPixel(cx, fr_y);
            color3 = img.getPixel(fr_x, cy);
            color4 = img.getPixel(cx, cy);

            // Blue
            bp1 = (byte) (nx * Color.blue(color1) + fx * Color.blue(color2));
            bp2 = (byte) (nx * Color.blue(color3) + fx * Color.blue(color4));
            nBlue = (byte) (ny * (double) (bp1) + fy * (double) (bp2));

            // Green
            bp1 = (byte) (nx * Color.green(color1) + fx * Color.green(color2));
            bp2 = (byte) (nx * Color.green(color3) + fx * Color.green(color4));
            nGreen = (byte) (ny * (double) (bp1) + fy * (double) (bp2));

            // Red
            bp1 = (byte) (nx * Color.red(color1) + fx * Color.red(color2));
            bp2 = (byte) (nx * Color.red(color3) + fx * Color.red(color4));
            nRed = (byte) (ny * (double) (bp1) + fy * (double) (bp2));

            bmap.setPixel(x, y, Color.argb(255, nRed, nGreen, nBlue));
        }
    }

    bmap = setGrayscale(bmap);
    bmap = removeNoise(bmap);

    return bmap;
}

// SetGrayscale
private Bitmap setGrayscale(Bitmap img) {
    Bitmap bmap = img.copy(img.getConfig(), true);
    int c;
    for (int i = 0; i < bmap.getWidth(); i++) {
        for (int j = 0; j < bmap.getHeight(); j++) {
            c = bmap.getPixel(i, j);
            byte gray = (byte) (.299 * Color.red(c) + .587 * Color.green(c)
                    + .114 * Color.blue(c));

            bmap.setPixel(i, j, Color.argb(255, gray, gray, gray));
        }
    }
    return bmap;
}

// RemoveNoise
private Bitmap removeNoise(Bitmap bmap) {
    for (int x = 0; x < bmap.getWidth(); x++) {
        for (int y = 0; y < bmap.getHeight(); y++) {
            int pixel = bmap.getPixel(x, y);
            if (Color.red(pixel) < 162 && Color.green(pixel) < 162 && Color.blue(pixel) < 162) {
                bmap.setPixel(x, y, Color.BLACK);
            }
        }
    }
    for (int x = 0; x < bmap.getWidth(); x++) {
        for (int y = 0; y < bmap.getHeight(); y++) {
            int pixel = bmap.getPixel(x, y);
            if (Color.red(pixel) > 162 && Color.green(pixel) > 162 && Color.blue(pixel) > 162) {
                bmap.setPixel(x, y, Color.WHITE);
            }
        }
    }
    return bmap;
}

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