BitmapCompressTools.java

package cn.com.scitc.swl.rssnews.tools;

import android.content.res.Resources;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;

/**
 * 这个类完成了对大图片的压缩
 * 
 * @author ASHENG
 * 
 */
public class BitmapCompressTools {

	public BitmapCompressTools() {
		// TODO Auto-generated constructor stub
	}

	/**
	 * 从资源文件中压缩bitmap
	 * 
	 * @param res
	 * @param resId
	 * @param reqWidth
	 * @param reqHeight
	 * @return
	 */
	public static Bitmap decodeSampledBitmapFromResource(Resources res,
			int resId, int reqWidth, int reqHeight) {
		// First decode with inJustDecodeBounds=true to check dimensions
		// 给定的bitmapfactory设置解码的参数
		final BitmapFactory.Options options = new BitmapFactory.Options();
		// 从解码器中获得原始图片的宽高而避免申请内存空间
		options.inJustDecodeBounds = true;
		BitmapFactory.decodeResource(res, resId, options);

		// Calculate inSampleSize
		options.inSampleSize = calculateInSampleSize(options, reqWidth,
				reqHeight);

		// Decode bitmap with inSampleSize set
		options.inJustDecodeBounds = false;
		return BitmapFactory.decodeResource(res, resId, options);
	}

	/**
	 * 从字节中压缩bitmap
	 * 
	 * @param data
	 * @param reqWidth
	 * @param reqHeight
	 * @return
	 */
	public static Bitmap decodeSampledBitmapFromByte(byte[] data, int reqWidth,
			int reqHeight) {
		// First decode with inJustDecodeBounds=true to check dimensions
		final BitmapFactory.Options options = new BitmapFactory.Options();
		options.inJustDecodeBounds = true;
		BitmapFactory.decodeByteArray(data, 0, data.length, options);

		// Calculate inSampleSize
		options.inSampleSize = calculateInSampleSize(options, reqWidth,
				reqHeight);

		// Decode bitmap with inSampleSize set
		options.inJustDecodeBounds = false;
		return BitmapFactory.decodeByteArray(data, 0, data.length, options);
	}

	/**
	 * 指定输出图片的缩放比例
	 * 
	 * @param options
	 * @param reqWidth
	 * @param reqHeight
	 * @return
	 */
	public static int calculateInSampleSize(BitmapFactory.Options options,
			int reqWidth, int reqHeight) {
		// Raw height and width of image
		final int height = options.outHeight;
		final int width = options.outWidth;
		int inSampleSize = 1;

		if (height > reqHeight || width > reqWidth) {

			final int halfHeight = height / 2;
			final int halfWidth = width / 2;

			// Calculate the largest inSampleSize value that is a power of 2 and
			// keeps both
			// height and width larger than the requested height and width.
			while ((halfHeight / inSampleSize) > reqHeight
					&& (halfWidth / inSampleSize) > reqWidth) {
				inSampleSize *= 2;
			}
		}

		return inSampleSize;
	}

}