Xamarin:Android - OutOfMemory exception with large bitmap - how to solve?

Question

I am taking an image, decoding the byte array that is generated by TakePicture method and then rotating the bitmap 270 degrees. The problem is that i seem to run out of memory, and i do not know how to solve it. Here is the code:

Bitmap image = BitmapFactory.DecodeByteArray (data, 0, data.Length);
data = null;
Bitmap rotatedBitmap = Bitmap.CreateBitmap (image, 0, 0, image.Width,
    image.Height, matrix, true);

i cannot make images smaller.. i need them as big as posible for OCR — Bogdan Constantin
– Bogdan Constantin, Commented Feb 7, 2016 at 14:32

Let'sRefactor · Accepted Answer · 2017-12-20 08:01:13Z

2

Please have a look at Load Large Bitmaps Efficiently from official Xamarin documentation, which explains how you can load large images into memory without the application throwing an OutOfMemoryException by loading a smaller subsampled version in memory.

Read Bitmap Dimensions and Type

async Task<BitmapFactory.Options> GetBitmapOptionsOfImageAsync()
{
    BitmapFactory.Options options = new BitmapFactory.Options
    {
        InJustDecodeBounds = true
    };

    // The result will be null because InJustDecodeBounds == true.
    Bitmap result=  await BitmapFactory.DecodeResourceAsync(Resources, Resource.Drawable.someImage, options);

    int imageHeight = options.OutHeight;
    int imageWidth = options.OutWidth;

    _originalDimensions.Text = string.Format("Original Size= {0}x{1}", imageWidth, imageHeight);

    return options;
}

Load a Scaled Down Version into Memory

public static int CalculateInSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight)
{
    // Raw height and width of image
    float height = options.OutHeight;
    float width = options.OutWidth;
    double inSampleSize = 1D;

    if (height > reqHeight || width > reqWidth)
    {
        int halfHeight = (int)(height / 2);
        int halfWidth = (int)(width / 2);

        // Calculate a inSampleSize that is a power of 2 - the decoder will use a value that is a power of two anyway.
        while ((halfHeight / inSampleSize) > reqHeight && (halfWidth / inSampleSize) > reqWidth)
        {
            inSampleSize *= 2;
        }
    }

    return (int)inSampleSize;
}

Load the Image as Async

public async Task<Bitmap> LoadScaledDownBitmapForDisplayAsync(Resources res, BitmapFactory.Options options, int reqWidth, int reqHeight)
{
    // Calculate inSampleSize
    options.InSampleSize = CalculateInSampleSize(options, reqWidth, reqHeight);

    // Decode bitmap with inSampleSize set
    options.InJustDecodeBounds = false;

    return await BitmapFactory.DecodeResourceAsync(res, Resource.Drawable.someImage, options);
}

And call it to load Image, say in OnCreate

protected async override void OnCreate(Bundle bundle)
{
    base.OnCreate(bundle);
    SetContentView(Resource.Layout.Main);
    _imageView = FindViewById<ImageView>(Resource.Id.resized_imageview);

    BitmapFactory.Options options = await GetBitmapOptionsOfImageAsync();
    Bitmap bitmapToDisplay = await LoadScaledDownBitmapForDisplayAsync (Resources, 
                             options, 
                             150,  //for 150 X 150 resolution
                             150);
    _imageView.SetImageBitmap(bitmapToDisplay);
}

Hope it helps.

edited Dec 20, 2017 at 8:01

answered Feb 7, 2016 at 19:10

Let'sRefactor

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4 Comments

Bogdan Constantin Over a year ago

i need the bitmap as big as it can be

Let'sRefactor Over a year ago

This sample is given for loading 150 X 150, please tweak it load the resolution you wanted for you app. @BogdanConstantin

Jay Kannan Over a year ago

I can't seem to use Resource.Drawable.samoyed - what is that?

Let'sRefactor Over a year ago

it's just an example, say, some image in your Drawable. corrected to avoid confusion

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