ImageUtils.java

/**
 * Make bitmap appropriate size, greyscale and inverted. MNIST model is originally teached on
 * dataset of images 28x28px with white letter written on black background.
 */
public static Bitmap prepareImageForClassification(Bitmap bitmap) {
    ColorMatrix colorMatrix = new ColorMatrix();
    colorMatrix.setSaturation(0);
    colorMatrix.postConcat(BLACKWHITE);
    colorMatrix.postConcat(INVERT);
    ColorMatrixColorFilter f = new ColorMatrixColorFilter(colorMatrix);

    Paint paint = new Paint();
    paint.setColorFilter(f);

    Bitmap bmpGrayscale = Bitmap.createScaledBitmap(
            bitmap,
            MnistModelConfig.INPUT_IMG_SIZE_WIDTH,
            MnistModelConfig.INPUT_IMG_SIZE_HEIGHT,
            false);
    Canvas canvas = new Canvas(bmpGrayscale);
    canvas.drawBitmap(bmpGrayscale, 0, 0, paint);
    return bmpGrayscale;
}