Loading Large Bitmaps Efficiently

Read Bitmap Dimensions and Type

To avoid java.lang.OutOfMemory exceptions, check the dimensions of a bitmap before decoding it:

BitmapFactory.Options options = new BitmapFactory.Options();
//Setting true while decoding avoids memory allocation
options.inJustDecodeBounds = true;
BitmapFactory.decodeResource(getResources(), R.id.myimage, options);
int imageHeight = options.outHeight;
int imageWidth = options.outWidth;
String imageType = options.outMimeType;

Load a Scaled Down Version into Memory

To tell the decoder to subsample the image, loading a smaller version into memory, set inSampleSize in your BitmapFactory. For example, an image with resolution 2048x1536 that is decoded with an inSampleSize of 4 produces a bitmap of approximately 512x384. Loading this into memory uses 0.75MB rather than 12MB for the full image.

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;
}

public static 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; //not load to memory
    BitmapFactory.decodeResource(res, resId, options); //returning null

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

    // Decode bitmap with inSampleSize set
    options.inJustDecodeBounds = false;//load to memory for actually decode
    return BitmapFactory.decodeResource(res, resId, options);
}

//How to use:
    mImageView.setImageBitmap(
    decodeSampledBitmapFromResource(getResources(), R.id.myimage, 100, 100));

When decode the image, speed depend on reading from disk or network, size of image, power of CPU. AsyncTask is an typical way to handle this:

class BitmapWorkerTask extends AsyncTask {
    private final WeakReference imageViewReference;

    public BitmapWorkerTask(ImageView imageView) {
        // Use a WeakReference to ensure the ImageView can be garbage collected
        imageViewReference = new WeakReference(imageView);
    }

    @Override
    protected Bitmap doInBackground(Integer... params) {
        return decodeSampledBitmapFromResource(getResources(), data, 100, 100));
    }

    // Once complete, see if ImageView is still around and set bitmap.
    @Override
    protected void onPostExecute(Bitmap bitmap) {
        if (imageViewReference != null && bitmap != null) {
            final ImageView imageView = imageViewReference.get();
            if (imageView != null) {
                imageView.setImageBitmap(bitmap);
            }
        }
    }
}

Handle Concurrency(ListView, GridView):

An example from android blog to handle loading bitmap into listview using AsyncTask: Multithreading for Performance

Personal example to loading thumbnails from internet: Image downloader in List/Recycle View

Create a dedicated Drawable subclass to store a reference back to the worker task. In this case, a BitmapDrawable is used so that a placeholder image can be displayed in the ImageView while the task completes:

static class AsyncDrawable extends BitmapDrawable {
    private final WeakReference bitmapWorkerTaskReference;

    public AsyncDrawable(Resources res, Bitmap bitmap,
            BitmapWorkerTask bitmapWorkerTask) {
        super(res, bitmap);
        bitmapWorkerTaskReference =
            new WeakReference(bitmapWorkerTask);
    }
    }

    public BitmapWorkerTask getBitmapWorkerTask() {
        return bitmapWorkerTaskReference.get();
    }
    
    public void loadBitmap(int resId, ImageView imageView) {
    if (cancelPotentialWork(resId, imageView)) {
        final BitmapWorkerTask task = new BitmapWorkerTask(imageView);
        final AsyncDrawable asyncDrawable =
                new AsyncDrawable(getResources(), mPlaceHolderBitmap, task);
        imageView.setImageDrawable(asyncDrawable);
        task.execute(resId);
    }
}

public static boolean cancelPotentialWork(int data, ImageView imageView) {
    final BitmapWorkerTask bitmapWorkerTask = getBitmapWorkerTask(imageView);

    if (bitmapWorkerTask != null) {
        final int bitmapData = bitmapWorkerTask.data;
        // If bitmapData is not yet set or it differs from the new data
        if (bitmapData == 0 || bitmapData != data) {
            // Cancel previous task
            bitmapWorkerTask.cancel(true);
        } else {
            // The same work is already in progress
            return false;
        }
    }
    // No task associated with the ImageView, or an existing task was cancelled
    return true;
}

private static BitmapWorkerTask getBitmapWorkerTask(ImageView imageView) {
   if (imageView != null) {
       final Drawable drawable = imageView.getDrawable();
       if (drawable instanceof AsyncDrawable) {
           final AsyncDrawable asyncDrawable = (AsyncDrawable) drawable;
           return asyncDrawable.getBitmapWorkerTask();
       }
    }
    return null;
}

class BitmapWorkerTask extends AsyncTask {
    ...

    @Override
    protected void onPostExecute(Bitmap bitmap) {
        if (isCancelled()) {
            bitmap = null;
        }

        if (imageViewReference != null && bitmap != null) {
            final ImageView imageView = imageViewReference.get();
            final BitmapWorkerTask bitmapWorkerTask =
                    getBitmapWorkerTask(imageView);
            if (this == bitmapWorkerTask && imageView != null) {
                imageView.setImageBitmap(bitmap);
            }
        }
    }
}

Processing Bitmaps Off the UI Thread

Caching Bitmaps

Managing Bitmap Memory

Displaying Bitmaps in Your UI