android - 在运行时减小位图的大小

Question

我正在使用尺寸很大的位图。在内存中加载位图时，它给了我 outofmemoryexception 有没有办法在不改变高度、宽度和质量的情况下减小大小。

Answer 1

通过这些课程有效地显示位图：http: //developer.android.com/training/displaying-bitmaps/index.html

Answer 2

使用此代码减小您需要减少图像尺寸的图像大小

public static Bitmap getResizedBitmap(Bitmap image, int newHeight, int newWidth) {
    int width = image.getWidth();
    int height = image.getHeight();
    float scaleWidth = ((float) newWidth) / width;
    float scaleHeight = ((float) newHeight) / height;
    // create a matrix for the manipulation
    Matrix matrix = new Matrix();
    // resize the bit map
    matrix.postScale(scaleWidth, scaleHeight);
    // recreate the new Bitmap
    Bitmap resizedBitmap = Bitmap.createBitmap(image, 0, 0, width, height,
            matrix, false);
    return resizedBitmap;
}

Answer 3

以下代码将在运行时为您提供屏幕分辨率。

DisplayMetrics displaymetrics = new DisplayMetrics();
getWindowManager().getDefaultDisplay().getMetrics(displaymetrics);
deviceHeightPix = displaymetrics.heightPixels;
deviceWidthPix = displaymetrics.widthPixels;

并且您可以根据需要在以下功能中传递这些高度和宽度或分辨率。此函数将返回从原始样本创建的样本大小。它不会降低任何质量。例如，您的屏幕尺寸为 480 * 800（普通和中等密度）而您的图像尺寸为 1500*2000，所以首先获取您的屏幕尺寸，传递给以下函数，它将返回 480*800 分辨率的图像而不减小其质量。

public Bitmap decodeSampledBitmapFromResource(Resources res, int resId,
        int reqWidth, int reqHeight) {

    // First decode with inJustDecodeBounds=true to check dimensions
    final BitmapFactory.Options options = new BitmapFactory.Options();
    options.inJustDecodeBounds = true;
    BitmapFactory.decodeResource(res, resId, options);

    Log.d("Home", "Image Resizer -> ReqHieght : " + reqHeight);
    Log.d("Home", "Image Resizer -> ReqWidth  : " + reqWidth);

    // Calculate inSampleSize
    options.inSampleSize = calculateInSampleSize(options, reqWidth,
            reqHeight);
    Log.d("Home", "Image Resizer -> Samplesize:" + options.inSampleSize);
    // Decode bitmap with inSampleSize set
    options.inJustDecodeBounds = false;
    return BitmapFactory.decodeResource(res, resId, options);
}

要使用上述功能，

Bitmap bitmap = DecodeSampledBitmapFromResource(getResources(),R.drawable.home_screen,480,800);

使用此功能的好处是，您无需TWO创建Bitmap. 第一个对象保存decoded图像，第二个对象使用第一个对象scale。

Answer 4

/**
 * decodes image and scales it to reduce memory consumption
 * 
 * @param file
 * @param requiredSize
 * @return
 */
public static Bitmap decodeFile(File file, int requiredSize) {
    try {

        // Decode image size
        BitmapFactory.Options o = new BitmapFactory.Options();
        o.inJustDecodeBounds = true;
        BitmapFactory.decodeStream(new FileInputStream(file), null, o);

        // The new size we want to scale to

        // Find the correct scale value. It should be the power of 2.
        int width_tmp = o.outWidth, height_tmp = o.outHeight;
        int scale = 1;
        while (true) {
            if (width_tmp / 2 < requiredSize
                    || height_tmp / 2 < requiredSize)
                break;
            width_tmp /= 2;
            height_tmp /= 2;
            scale *= 2;
        }

        // Decode with inSampleSize
        BitmapFactory.Options o2 = new BitmapFactory.Options();
        o2.inSampleSize = scale;

        Bitmap bmp = BitmapFactory.decodeStream(new FileInputStream(file),
                null, o2);

        return bmp;

    } catch (FileNotFoundException e) {
    } finally {
    }
    return null;
}