How do I scale a streaming bitmap in-place without reading the whole image first?

Question

I have an Android application that is very image intensive. I\'m currently using Bitmap.createScaledBitmap() to scale the image to a desired size. However, this method requi

Answer 1

Here is my version, based on @emmby solution (thanks man!) I've included a second phase where you take the reduced bitmap and scale it again to match exactly your desired dimensions. My version takes a file path rather than a stream.

protected Bitmap createScaledBitmap(String filePath, int desiredBitmapWith, int desiredBitmapHeight) throws IOException, FileNotFoundException {
    BufferedInputStream imageFileStream = new BufferedInputStream(new FileInputStream(filePath));
    try {
        // Phase 1: Get a reduced size image. In this part we will do a rough scale down
        int sampleSize = 1;
        if (desiredBitmapWith > 0 && desiredBitmapHeight > 0) {
            final BitmapFactory.Options decodeBoundsOptions = new BitmapFactory.Options();
            decodeBoundsOptions.inJustDecodeBounds = true;
            imageFileStream.mark(64 * 1024);
            BitmapFactory.decodeStream(imageFileStream, null, decodeBoundsOptions);
            imageFileStream.reset();
            final int originalWidth = decodeBoundsOptions.outWidth;
            final int originalHeight = decodeBoundsOptions.outHeight;
            // inSampleSize prefers multiples of 2, but we prefer to prioritize memory savings
            sampleSize = Math.max(1, Math.max(originalWidth / desiredBitmapWith, originalHeight / desiredBitmapHeight));
        }
        BitmapFactory.Options decodeBitmapOptions = new BitmapFactory.Options();
        decodeBitmapOptions.inSampleSize = sampleSize;
        decodeBitmapOptions.inPreferredConfig = Bitmap.Config.RGB_565; // Uses 2-bytes instead of default 4 per pixel

        // Get the roughly scaled-down image
        Bitmap bmp = BitmapFactory.decodeStream(imageFileStream, null, decodeBitmapOptions);

        // Phase 2: Get an exact-size image - no dimension will exceed the desired value
        float ratio = Math.min((float)desiredBitmapWith/ (float)bmp.getWidth(), (float)desiredBitmapHeight/ (float)bmp.getHeight());
        int w =(int) ((float)bmp.getWidth() * ratio);
        int h =(int) ((float)bmp.getHeight() * ratio);
        return Bitmap.createScaledBitmap(bmp, w,h, true);

    } catch (IOException e) {
        throw e;
    } finally {
        try {
            imageFileStream.close();
        } catch (IOException ignored) {
        }
    }
}