android - calculateInSampleSize, why does Math.round deal with height( height / reqHeight) when width > height?

Question

I'm looking on 'developer.android.com' to scale down my bitmap file and I found one thing that I don't understand. so I appreciate you give me a little help.

Here's a snippet from developer.android.com

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) {
    if (width > height) {
      inSampleSize = Math.round((float)height / (float)reqHeight);
    } else {
      inSampleSize = Math.round((float)width / (float)reqWidth);
    }
  }
  return inSampleSize;
}

in if statement, when " if(width > height)" why do they calculate "(float)height / (float)reqHeight " ?

for example, width=600, height=800, reqWidth=100, reqHeight=100.

In this situation, inSampleSize would be 6 and the dimensions calculated are width=100, height=133. height is still above reqHeight..

so, can anyone explain me about this, please? sorry for complicated explanation but I hope someone give me a idea. :)

Answer 1

All I can say is that their logic looks wrong :( Anyway this method is fairly simple so it shouldn't be that much of a problem for you to reimplement it with the correct conditions ! I mean when you take a look at decodeSampledBitmapFromResource, it only wants to reduce the Bitmap to make it fit into the desired bounds, so this has to be an error.

EDIT :: That looks even worse as to me it won't work for some cases. Let's say you have width = 200 and height = 600. You set your max bounds at width = 100 and height = 500. You have height > width, yet if you want them both to fit the return result inSampleSize has to be 200/100 and not 600/500. So basically if you reimplement the method, I would do it this way :

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 stretch_width = Math.round((float)width / (float)reqWidth);
    int stretch_height = Math.round((float)height / (float)reqHeight);

    if (stretch_width <= stretch_height) 
        return stretch_height;
    else 
        return stretch_width;
}

But that looks like too many issues with their code for me to believe I understood its point correctly !