图片压缩

android 系统的图片压缩大体上有三种方式，质量压缩，比例压缩，采样率压缩


质量压缩
public static Bitmap getCompressBitmapByQuality(Bitmap bitmap, int quality) {
            ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
            bitmap.compress(Bitmap.CompressFormat.JPEG, quality, outputStream);
            ByteArrayInputStream inputStream = new ByteArrayInputStream(outputStream.toByteArray());
            return BitmapFactory.decodeStream(inputStream, null, null);
    }


比例压缩
public static Bitmap getCompressBitmapByScale(Bitmap bitmap, int maxW, int maxH) {
        int w = bitmap.getWidth();
        int h = bitmap.getHeight();


        float sx = (float) maxW / (float) w;
        float sy = (float) maxH / (float) h;


        Matrix matrix = new Matrix();
        matrix.setScale(sx, sy);
        return Bitmap.createBitmap(bitmap, 0, 0, bitmap.getWidth(), bitmap.getHeight(), matrix, true);
}


采样率压缩
public static Bitmap getCompressBitmapBySampleSize(Bitmap bitmap, int sampleSize) {
        BitmapFactory.Options options = new BitmapFactory.Options();
        options.inSampleSize = sampleSize;


        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
        bitmap.compress(Bitmap.CompressFormat.JPEG, 100, outputStream);
        return BitmapFactory.decodeByteArray(outputStream.toByteArray(), 0, outputStream.toByteArray().length, options);
}


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;
}