How to resize image (Bitmap) to a given size? [duplicate]

Question

Bitmap scaledBitmap = scaleDown(realImage, MAX_IMAGE_SIZE, true);

Scale down method:

public static Bitmap scaleDown(Bitmap realImage, float maxImageSize,
        boolean filter) {
    float ratio = Math.min(
            (float) maxImageSize / realImage.getWidth(),
            (float) maxImageSize / realImage.getHeight());
    int width = Math.round((float) ratio * realImage.getWidth());
    int height = Math.round((float) ratio * realImage.getHeight());

    Bitmap newBitmap = Bitmap.createScaledBitmap(realImage, width,
            height, filter);
    return newBitmap;
}

 Bitmap yourBitmap;
 Bitmap resized = Bitmap.createScaledBitmap(yourBitmap, newWidth, newHeight, true);

or:

 resized = Bitmap.createScaledBitmap(yourBitmap,(int)(yourBitmap.getWidth()*0.8), (int)(yourBitmap.getHeight()*0.8), true);

You can scale bitmaps by using canvas.drawBitmap with providing matrix, for example:

public static Bitmap scaleBitmap(Bitmap bitmap, int wantedWidth, int wantedHeight) {
        Bitmap output = Bitmap.createBitmap(wantedWidth, wantedHeight, Config.ARGB_8888);
        Canvas canvas = new Canvas(output);
        Matrix m = new Matrix();
        m.setScale((float) wantedWidth / bitmap.getWidth(), (float) wantedHeight / bitmap.getHeight());
        canvas.drawBitmap(bitmap, m, new Paint());

        return output;
    }

The other answers are correct as to "how" to resize them, but I would also thrown in the recommendation to just grab the resolution you are interested in, to begin with. Most Android devices offer a range of resolutions and you should pick one that gives you a file size that you're comfortable with. The biggest reason for this is that the native Android scaling algorithm (as detailed by Jin35 and Padma Kumar) produces pretty crappy results. It's not going to give you Photoshop quality resizing, even downscaling (to say nothing of upscaling, which I know you're not asking about, but that's just a non-starter).

So, you should try their solution and if you're happy with the outcome, great. But if not, I'd write a function that offers a range of width that you're happy with, and looks for that dimension (or whatever's closest) in the device's available picture size array and just set it and use it.

In MonoDroid here's how (c#)

/// <summary>
/// Graphics support for resizing images
/// </summary>
public static class Graphics
{
    public static Bitmap ScaleDownBitmap(Bitmap originalImage, float maxImageSize, bool filter)
    {
        float ratio = Math.Min((float)maxImageSize / originalImage.Width, (float)maxImageSize / originalImage.Height);
        int width = (int)Math.Round(ratio * (float)originalImage.Width);
        int height =(int) Math.Round(ratio * (float)originalImage.Height);

        Bitmap newBitmap = Bitmap.CreateScaledBitmap(originalImage, width, height, filter);
        return newBitmap;
    }

    public static Bitmap ScaleBitmap(Bitmap originalImage, int wantedWidth, int wantedHeight)
    {
        Bitmap output = Bitmap.CreateBitmap(wantedWidth, wantedHeight, Bitmap.Config.Argb8888);
        Canvas canvas = new Canvas(output);
        Matrix m = new Matrix();
        m.SetScale((float)wantedWidth / originalImage.Width, (float)wantedHeight / originalImage.Height);
        canvas.DrawBitmap(originalImage, m, new Paint());
        return output;
    }

}