如何使用Android / Java加快图像处理速度？

Question

I was following some Java code to do image processing on bitmaps and found that it was really time consuming for the user.

How could this be done faster in code?

Right now it's taking too long pixel by pixel

I read somewhere about storing it into an 2d array first? Matrix ?

public static Bitmap createContrast(Bitmap src, double value) {
    // image size
    int width = src.getWidth();
    int height = src.getHeight();
    // create output bitmap
    Bitmap bmOut = Bitmap.createBitmap(width, height, src.getConfig());
    // color information
    int A, R, G, B;
    int pixel;
    // get contrast value
    double contrast = Math.pow((100 + value) / 100, 2);

    // scan through all pixels
    for(int x = 0; x < width; ++x) {
        for(int y = 0; y < height; ++y) {
            // get pixel color
            pixel = src.getPixel(x, y);
            A = Color.alpha(pixel);
            // apply filter contrast for every channel R, G, B
            R = Color.red(pixel);
            R = (int)(((((R / 255.0) - 0.5) * contrast) + 0.5) * 255.0);
            if(R < 0) { R = 0; }
            else if(R > 255) { R = 255; }

            G = Color.red(pixel);
            G = (int)(((((G / 255.0) - 0.5) * contrast) + 0.5) * 255.0);
            if(G < 0) { G = 0; }
            else if(G > 255) { G = 255; }

            B = Color.red(pixel);
            B = (int)(((((B / 255.0) - 0.5) * contrast) + 0.5) * 255.0);
            if(B < 0) { B = 0; }
            else if(B > 255) { B = 255; }

            // set new pixel color to output bitmap
            bmOut.setPixel(x, y, Color.argb(A, R, G, B));
        }
    }

    // return final image
    return bmOut;
}

Answer 1

I propose using getPixels and setPixels so that you can manipulate the array directly. I haven't run this, but it should give you the idea:

int[] pixels = new int[width * height];
bmOut.getPixels(pixels, 0, width, 0, 0, width, height);
// scan through all pixels
for(int i = 0; i < width * height; i++) {
    // get pixel color
    // pixel = src.getPixel(x, y);
    pixel = pixels[i];
    A = Color.alpha(pixel);
    // apply filter contrast for every channel R, G, B
    R = Color.red(pixel);
    R = (int)(((((R / 255.0) - 0.5) * contrast) + 0.5) * 255.0);
    if(R < 0) { R = 0; }
    else if(R > 255) { R = 255; }

    G = Color.green(pixel);
    G = (int)(((((G / 255.0) - 0.5) * contrast) + 0.5) * 255.0);
    if(G < 0) { G = 0; }
    else if(G > 255) { G = 255; }

    B = Color.blue(pixel);
    B = (int)(((((B / 255.0) - 0.5) * contrast) + 0.5) * 255.0);
    if(B < 0) { B = 0; }
    else if(B > 255) { B = 255; }

    // set new pixel color to output bitmap
    pixels[i] = Color.argb(A, R, G, B);
}
bmOut.setPixels(pixels, 0, width, 0, 0, width, height);