Bitmap的优化套路很简单，粗暴，就是让压缩。
三种压缩方式：
- 对图片质量进行压缩
- 对图片尺寸进行压缩
- 使用libjpeg.so库进行压缩
对图片质量进行压缩
public static Bitmap compressImage(Bitmap bitmap){
ByteArrayOutputStream baos = new ByteArrayOutputStream();
//质量压缩方法，这里100表示不压缩，把压缩后的数据存放到baos中
bitmap.compress(Bitmap.CompressFormat.JPEG, 100, baos);
int options = 100;
//循环判断如果压缩后图片是否大于50kb,大于继续压缩
while ( baos.toByteArray().length / 1024>50) {
//清空baos
baos.reset();
bitmap.compress(Bitmap.CompressFormat.JPEG, options, baos);
options -= 10;//每次都减少10
}
//把压缩后的数据baos存放到ByteArrayInputStream中
ByteArrayInputStream isBm = new ByteArrayInputStream(baos.toByteArray());
//把ByteArrayInputStream数据生成图片
Bitmap newBitmap = BitmapFactory.decodeStream(isBm, null, null);
return newBitmap;
}
对图片尺寸进行压缩
/**
* 按图片尺寸压缩 参数是bitmap
* @param bitmap
* @param pixelW
* @param pixelH
* @return
*/
public static Bitmap compressImageFromBitmap(Bitmap bitmap, int pixelW, int pixelH) {
ByteArrayOutputStream os = new ByteArrayOutputStream();
bitmap.compress(Bitmap.CompressFormat.JPEG, 100, os);
if( os.toByteArray().length / 1024>512) {//判断如果图片大于0.5M,进行压缩避免在生成图片（BitmapFactory.decodeStream）时溢出
os.reset();
bitmap.compress(Bitmap.CompressFormat.JPEG, 50, os);//这里压缩50%，把压缩后的数据存放到baos中
}
ByteArrayInputStream is = new ByteArrayInputStream(os.toByteArray());
BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
options.inPreferredConfig = Bitmap.Config.RGB_565;
BitmapFactory.decodeStream(is, null, options);
options.inJustDecodeBounds = false;
options.inSampleSize = computeSampleSize(options , pixelH > pixelW ? pixelW : pixelH ,pixelW * pixelH );
is = new ByteArrayInputStream(os.toByteArray());
Bitmap newBitmap = BitmapFactory.decodeStream(is, null, options);
return newBitmap;
}
/**
* 动态计算出图片的inSampleSize
* @param options
* @param minSideLength
* @param maxNumOfPixels
* @return
*/
public static int computeSampleSize(BitmapFactory.Options options, int minSideLength, int maxNumOfPixels) {
int initialSize = computeInitialSampleSize(options, minSideLength, maxNumOfPixels);
int roundedSize;
if (initialSize <= 8) {
roundedSize = 1;
while (roundedSize < initialSize) {
roundedSize <<= 1;
}
} else {
roundedSize = (initialSize + 7) / 8 * 8;
}
return roundedSize;
}
private static int computeInitialSampleSize(BitmapFactory.Options options, int minSideLength, int maxNumOfPixels) {
double w = options.outWidth;
double h = options.outHeight;
int lowerBound = (maxNumOfPixels == -1) ? 1 : (int) Math.ceil(Math.sqrt(w * h / maxNumOfPixels));
int upperBound = (minSideLength == -1) ? 128 :(int) Math.min(Math.floor(w / minSideLength), Math.floor(h / minSideLength));
if (upperBound < lowerBound) {
return lowerBound;
}
if ((maxNumOfPixels == -1) && (minSideLength == -1)) {
return 1;
} else if (minSideLength == -1) {
return lowerBound;
} else {
return upperBound;
}
}
使用libjpeg.so库进行压缩
可以参考这篇Android性能优化系列之Bitmap图片优化：
https://blog.csdn.net/u012124438/article/details/66087785
摘自：《Android 性能优化最佳实践》任玉刚公众号
