How to resize image (Bitmap) to a given size?

Question

How to resize image (Bitmap) to for example 800*480 programatically ? I have retrieved a picture in my app which is ~1MB and I need to scale it down to 800*480 I have loaded that picture and compressed it but how do I do to make it smaller :

ByteArrayOutputStream bos = new ByteArrayOutputStream(8192);
photo.compress(CompressFormat.JPEG, 25, bos);

I have already answered this question here, https://stackoverflow.com/a/58820612/5701085 — Asad Ali Choudhry, Nov 12 '19 at 14:27

score 31 · Answer 1 · answered Aug 06 '14 at 09:54

31

 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);

answered Aug 06 '14 at 09:54

Vaishali Sutariya

5,093
30
32

in case you are wondering what the last boolean parameter is for: https://developer.android.com/reference/android/graphics/Bitmap#createScaledBitmap(android.graphics.Bitmap,%20int,%20int,%20boolean) – because_im_batman Jul 08 '22 at 20:16
How about resize only with width? – K.Sopheak Mar 13 '23 at 09:20

score 14 · Answer 2 · answered Dec 12 '11 at 07:45

14

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;
    }

answered Dec 12 '11 at 07:45

Jin35

8,602
3
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52

1

add flags to paint to improve downsampling quality: new Paint(6) – Denis Nek Feb 21 '17 at 02:38
1

6 = Paint.FILTER_BITMAP_FLAG | Paint.DITHER_FLAG https://developer.android.com/reference/android/graphics/Paint#ANTI_ALIAS_FLAG https://developer.android.com/reference/android/graphics/Paint#DITHER_FLAG – Ivan Shafran Oct 21 '18 at 14:35

score 2 · Answer 3 · answered Jun 11 '12 at 19:22

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;
    }

}

If I have a lot of images, where they are in different sizes in different activitys. Is it better to resize them in code or import them in small and large size. — paakjis, Apr 25 '17 at 13:47

score 2 · Answer 4 · answered Dec 12 '11 at 07:52

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.

How to resize image (Bitmap) to a given size?

4 Answers4

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