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Android 图片压缩
在android 中进行图片压缩处理, 通常是为了减小图片大小来节省存储空间或者加快网络传输速度.
本文主要记录下android 中原生的压缩图片方法.
1: 使用Bitmap.compress()方法压缩图片
示例代码1:
通过Bitmap的compress()方法将图片压缩为JPEG/PNG格式.
Bitmap bitmap=BitmapFactory.decodeResource(getResources(),R.drawable.image);
ByteArrayOutputStream os = new ByteArrayOutputStream();
bitmap.compress(Bitmap.CompressFormat.JPEG,80,os);
byte[] compressImage=os.toByteArray();
- compress方法中Bitmap.CompressFormat.JPEG指定压缩格式,
- 参数80: 压缩质量,范围是0-100,数值越小压缩率越高,当然图片的质量也越差.
由此我们可以延伸出限定图片大小,来循环压缩,具体代码如下:
/*** 压缩 Bitmap 到指定大小以内（KB）*/private static byte[] compressBitmap(Bitmap bitmap, int maxKb, Bitmap.CompressFormat format) {ByteArrayOutputStream outputStream = new ByteArrayOutputStream();int quality = 100;bitmap.compress(format, quality, outputStream);while (outputStream.toByteArray().length > maxKb * 1024 && quality > 10) {outputStream.reset();quality -= 5;bitmap.compress(format, quality, outputStream);}return outputStream.toByteArray();}
可以看到封装的方法指定maxKb, 初始化时质量为100,拿到图片的原始大小,从而根据大小来循环执行压缩方法.并逐渐降低压缩质量.
2: 缩放图片尺寸压缩
示例代码2:
Bitmap originalBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.image);
Bitmap scaledBitmap = Bitmap.createScaledBitmap(originalBitmap, 1024, 768, true);
ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
scaledBitmap.compress(Bitmap.CompressFormat.JPEG, 80, outputStream);
byte[] compressedImage = outputStream.toByteArray();
示例代码中将图片指定缩放到1024x768,并压缩质量值80.
private static Bitmap scaleBitmap(Bitmap bitmap, int targetWidth, int targetHeight) {return Bitmap.createScaledBitmap(bitmap, targetWidth, targetHeight, true);
}
3: 处理 EXIF 旋转
/*** 从 Uri 解码图片，并自动处理 EXIF 旋转*/private static Bitmap decodeBitmapFromUri(Context context, Uri uri) throws IOException {ContentResolver resolver = context.getContentResolver();InputStream inputStream = resolver.openInputStream(uri);BitmapFactory.Options options = new BitmapFactory.Options();options.inJustDecodeBounds = false;Bitmap bitmap = BitmapFactory.decodeStream(inputStream, null, options);inputStream.close();// 处理 EXIF 旋转ExifInterface exif = new ExifInterface(resolver.openInputStream(uri));int orientation = exif.getAttributeInt(ExifInterface.TAG_ORIENTATION, ExifInterface.ORIENTATION_NORMAL);Matrix matrix = new Matrix();switch (orientation) {case ExifInterface.ORIENTATION_ROTATE_90:matrix.postRotate(90);break;case ExifInterface.ORIENTATION_ROTATE_180:matrix.postRotate(180);break;case ExifInterface.ORIENTATION_ROTATE_270:matrix.postRotate(270);break;default:break;}return Bitmap.createBitmap(bitmap, 0, 0, options.outWidth, options.outHeight, matrix, true);}
4: 采样率压缩
采样率是BitmapFactory.Options的重要参数,用于控制图片解码时的缩放比例,合理的设置inSanmpleSize可以有效的减少内存占用,减少oom的出现.
采样率的计算主要通过实际大小以及要求大小来计算,具体的代码如下:
public static int calculateInSampleSize(int actualWidth, int actualHeight, int reqWidth, int reqHeight) {int inSampleSize = 1;if (actualHeight > reqHeight || actualWidth > reqWidth) {int halfWidth = actualWidth / 2;int halfHeight = actualHeight / 2;while ((halfWidth / inSampleSize) >= reqWidth&& (halfHeight / inSampleSize) >= reqHeight) {inSampleSize *= 2;}}return inSampleSize;
}获取图片的原始大小, 我们可以通过
BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true; // 只读取元数据，不解码像素
InputStream is = context.getContentResolver().openInputStream(uri);
BitmapFactory.decodeStream(is, null, options);
is.close();
原始图片的宽高,就可以从options.outWidth 和 options.outHeight 得到.
5: 附上源码
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Matrix;
import android.media.ExifInterface;
import android.net.Uri;
import android.os.Build;
import android.content.ContentResolver;
import android.content.Context;import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;public class ImageCompressUtils {/*** 压缩图片到指定最大大小（单位 KB），并返回压缩后的字节数组** @param context 上下文* @param uri 图片 Uri* @param maxKb 最大允许大小（KB）* @param format 压缩格式（Bitmap.CompressFormat）* @param inSampleSize 采样率（2 的幂次，例如 1, 2, 4, 8...）* @return 压缩后的图片字节数组*/public static byte[] compressImage(Context context, Uri uri, int maxKb, Bitmap.CompressFormat format, int inSampleSize) throws IOException {Bitmap bitmap = decodeBitmapFromUri(context, uri, inSampleSize);return compressBitmap(bitmap, maxKb, format);}/*** 缩放并压缩图片到指定宽高和大小** @param context 上下文* @param uri 图片 Uri* @param targetWidth 目标宽度* @param targetHeight 目标高度* @param maxKb 最大允许大小（KB）* @param format 压缩格式* @param inSampleSize 采样率（2 的幂次）* @return 压缩后的图片字节数组*/public static byte[] compressToSize(Context context, Uri uri, int targetWidth, int targetHeight, int maxKb, Bitmap.CompressFormat format, int inSampleSize) throws IOException {Bitmap original = decodeBitmapFromUri(context, uri, inSampleSize);Bitmap scaled = scaleBitmap(original, targetWidth, targetHeight);return compressBitmap(scaled, maxKb, format);}/*** 从 Uri 解码图片，支持指定采样率，并自动处理 EXIF 旋转*/private static Bitmap decodeBitmapFromUri(Context context, Uri uri, int inSampleSize) throws IOException {ContentResolver resolver = context.getContentResolver();InputStream inputStream = resolver.openInputStream(uri);BitmapFactory.Options options = new BitmapFactory.Options();options.inJustDecodeBounds = false;options.inSampleSize = inSampleSize; // 设置采样率Bitmap bitmap = BitmapFactory.decodeStream(inputStream, null, options);inputStream.close();// 处理 EXIF 旋转ExifInterface exif = new ExifInterface(resolver.openInputStream(uri));int orientation = exif.getAttributeInt(ExifInterface.TAG_ORIENTATION, ExifInterface.ORIENTATION_NORMAL);Matrix matrix = new Matrix();switch (orientation) {case ExifInterface.ORIENTATION_ROTATE_90:matrix.postRotate(90);break;case ExifInterface.ORIENTATION_ROTATE_180:matrix.postRotate(180);break;case ExifInterface.ORIENTATION_ROTATE_270:matrix.postRotate(270);break;default:break;}return Bitmap.createBitmap(bitmap, 0, 0, options.outWidth, options.outHeight, matrix, true);}/*** 缩放图片到指定宽高*/private static Bitmap scaleBitmap(Bitmap bitmap, int targetWidth, int targetHeight) {return Bitmap.createScaledBitmap(bitmap, targetWidth, targetHeight, true);}/*** 压缩 Bitmap 到指定大小以内（KB）*/private static byte[] compressBitmap(Bitmap bitmap, int maxKb, Bitmap.CompressFormat format) {ByteArrayOutputStream outputStream = new ByteArrayOutputStream();int quality = 100;bitmap.compress(format, quality, outputStream);while (outputStream.toByteArray().length > maxKb * 1024 && quality > 10) {outputStream.reset();quality -= 5;bitmap.compress(format, quality, outputStream);}return outputStream.toByteArray();}/*** 自动计算合适的采样率（inSampleSize）** @param actualWidth 实际宽度* @param actualHeight 实际高度* @param reqWidth 请求宽度* @param reqHeight 请求高度* @return 合适的采样率*/public static int calculateInSampleSize(int actualWidth, int actualHeight, int reqWidth, int reqHeight) {int inSampleSize = 1;if (actualHeight > reqHeight || actualWidth > reqWidth) {int halfWidth = actualWidth / 2;int halfHeight = actualHeight / 2;while ((halfWidth / inSampleSize) >= reqWidth&& (halfHeight / inSampleSize) >= reqHeight) {inSampleSize *= 2;}}return inSampleSize;}
}