BitmapUtils.java

import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Rect;

/**
 * Created by thom on 2018/9/23.
 */
public class BitmapUtils {

    static Bitmap crop(Bitmap bitmap) {
        int width = bitmap.getWidth();
        int height = bitmap.getHeight();
        int left = 0;
        int right = width;
        int top = 0;
        int bottom = height;

        while (left < width) {
            int pixel = bitmap.getPixel(left, height / 2);
            if (Color.alpha(pixel) != 0) {
                break;
            }
            left++;
        }

        while (right > 0) {
            int pixel = bitmap.getPixel(right - 1, height / 2);
            if (Color.alpha(pixel) != 0) {
                break;
            }
            right--;
        }

        while (top < height) {
            int pixel = bitmap.getPixel(width / 2, top);
            if (Color.alpha(pixel) != 0) {
                break;
            }
            top++;
        }

        while (bottom > 0) {
            int pixel = bitmap.getPixel(width / 2, bottom - 1);
            if (Color.alpha(pixel) != 0) {
                break;
            }
            bottom--;
        }

        if (left == 0 && top == 0 && right == width && bottom == height) {
            return bitmap;
        }

        Bitmap crop = Bitmap.createBitmap(right - left, bottom - top, Bitmap.Config.ARGB_8888);
        Canvas canvas = new Canvas(crop);
        Rect src = new Rect(left, top, right, bottom);
        Rect dst = new Rect(0, 0, crop.getWidth(), crop.getHeight());
        canvas.drawBitmap(bitmap, src, dst, null);

        return crop;
    }

}