1、算法

第一步：从右下到左上遍历图片像素

第二步：获取当前像素和 左上点像素，分别取它们RGB的差值

第三步：获取三个差值中绝对值最大的一个作为灰度值

第四步：将该灰度值加128 ，并且作像素安全处理（即gray = gray>255?255:gray , gray = gray<0 ? 0 : gray）

第五步：使用该灰度值创建图片

2、实现代码

public Bitmap render(Bitmap bitmap)    {        if (bitmap == null)            return null;//        bitmap = toGray(bitmap);        int width = bitmap.getWidth();        int height = bitmap.getHeight();        int[] pixels = new int[width * height];        bitmap.getPixels(pixels, 0, width, 0, 0, width, height);        for (int i = height - 1; i > 0; i--)        {            for (int j = width - 1; j > 0; j--)            {                int pixel = pixels[i * width + j];                int leftUpPixel = pixels[(i - 1) * width + j - 1];                int r = (pixel & 0x00ff0000) >> 16;                int g = (pixel & 0x0000ff00) >> 8;                int b = (pixel & 0x000000ff);                                int leftUpR = (leftUpPixel & 0x00ff0000) >> 16;                int leftUpG = (leftUpPixel & 0x0000ff00) >> 8;                int leftUpB = (leftUpPixel & 0x000000ff);                                r = r - leftUpR;                g = g - leftUpG;                b = b - leftUpB;                                int maxDiff = r;                if(Math.abs(maxDiff) < Math.abs(g));                {                    maxDiff = g;                }                                if(Math.abs(maxDiff) < Math.abs(b))                {                    maxDiff = b;                }                                int gray = maxDiff +128;                        if(gray>255)gray = 255;                if(gray <0)gray = 0;                pixels[i * width + j] = (pixel & 0xff000000) + (gray << 16) + (gray << 8) + gray;            }        }        return Bitmap.createBitmap(pixels, width, height, Config.ARGB_8888);    }