Android开发实现去除bitmap无用白色边框的方法示例

import android.graphics.Bitmap;
/**
 * Created by Victor Yang on 2016/6/17.
 * 去除 bitmap 无用的白色边框
 */
public class BitmapDeleteNoUseSpaceUtil {
  /**
   * 灰度化 bitmap
   * @param imgTheWidth
   * @param imgTheHeight
   * @param imgThePixels
   * @return
   */
  private static Bitmap getGrayImg(int imgTheWidth, int imgTheHeight, int[] imgThePixels) {
    int alpha = 0xFF << 24; //设置透明度
    for (int i = 0; i < imgTheHeight; i++) {
      for (int j = 0; j < imgTheWidth; j++) {
        int grey = imgThePixels[imgTheWidth * i + j];
        int red = ((grey & 0x00FF0000) >> 16); //获取红色灰度值
        int green = ((grey & 0x0000FF00) >> 8); //获取绿色灰度值
        int blue = (grey & 0x000000FF);     //获取蓝色灰度值
        grey = (int) ((float) red * 0.3 + (float) green * 0.59 + (float) blue * 0.11);
        grey = alpha | (grey << 16) | (grey << 8) | grey; //添加透明度
        imgThePixels[imgTheWidth * i + j] = grey;  //更改像素色值
      }
    }
    Bitmap result =
        Bitmap.createBitmap(imgTheWidth, imgTheHeight, Bitmap.Config.RGB_565);
    result.setPixels(imgThePixels, 0, imgTheWidth, 0, 0, imgTheWidth, imgTheHeight);
    return result;
  }
  /**
   * 去除多余白框
   * @param originBitmap
   * @return
   */
  public static Bitmap deleteNoUseWhiteSpace(Bitmap originBitmap) {
    int[] imgThePixels = new int[originBitmap.getWidth() * originBitmap.getHeight()];
    originBitmap.getPixels(
        imgThePixels,
        0,
        originBitmap.getWidth(),
        0,
        0,
        originBitmap.getWidth(),
        originBitmap.getHeight());
    // 灰度化 bitmap
    Bitmap bitmap = getGrayImg(
        originBitmap.getWidth(),
        originBitmap.getHeight(),
        imgThePixels);
    int top = 0; // 上边框白色高度
    int left = 0; // 左边框白色高度
    int right = 0; // 右边框白色高度
    int bottom = 0; // 底边框白色高度
    for (int h = 0; h < bitmap.getHeight(); h++) {
      boolean holdBlackPix = false;
      for (int w = 0; w < bitmap.getWidth(); w++) {
        if (bitmap.getPixel(w, h) != -1) { // -1 是白色
          holdBlackPix = true; // 如果不是-1 则是其他颜色
          break;
        }
      }
      if (holdBlackPix) {
        break;
      }
      top++;
    }
    for (int w = 0; w < bitmap.getWidth(); w++) {
      boolean holdBlackPix = false;
      for (int h = 0; h < bitmap.getHeight(); h++) {
        if (bitmap.getPixel(w, h) != -1) {
          holdBlackPix = true;
          break;
        }
      }
      if (holdBlackPix) {
        break;
      }
      left++;
    }
    for (int w = bitmap.getWidth() - 1; w >= 0; w--) {
      boolean holdBlackPix = false;
      for (int h = 0; h < bitmap.getHeight(); h++) {
        if (bitmap.getPixel(w, h) != -1) {
          holdBlackPix = true;
          break;
        }
      }
      if (holdBlackPix) {
        break;
      }
      right++;
    }
    for (int h = bitmap.getHeight() - 1; h >= 0; h--) {
      boolean holdBlackPix = false;
      for (int w = 0; w < bitmap.getWidth(); w++) {
        if (bitmap.getPixel(w, h) != -1) {
          holdBlackPix = true;
          break;
        }
      }
      if (holdBlackPix) {
        break;
      }
      bottom++;
    }
    // 获取内容区域的宽高
    int cropHeight = bitmap.getHeight() - bottom - top;
    int cropWidth = bitmap.getWidth() - left - right;
    // 获取内容区域的像素点
    int[] newPix = new int[cropWidth * cropHeight];
    int i = 0;
    for (int h = top; h < top + cropHeight; h++) {
      for (int w = left; w < left + cropWidth; w++) {
        newPix[i++] = bitmap.getPixel(w, h);
      }
    }
    // 创建切割后的 bitmap， 针对彩色图，把 newPix 替换为 originBitmap 的 pixs
    return Bitmap.createBitmap(newPix, cropWidth, cropHeight, Bitmap.Config.ARGB_8888);
  }
}