Android ImageView scale image and center

Question

I need to scale an Image inside an ImageView, I need to use the matrix for doing so,

So I do;

private void scaleImage(float scaleFactor, float focusX,float focusY) {
    Matrix displayMatrix= new Matrix();
    matrix.postScale(scaleFactor, scaleFactor);
    displayMatrix.set(matrix);
    imageView.setImageMatrix(displayMatrix);
}

The problem is no matter what i am not able to center the image inside the ImageView,

I need to put the image at the center (leaving white margins if the image is smaller than the view)

I have been bangin my head for hours, please help.

I have looked extensively at this https://stackoverflow.com/a/6172226/1815311, but without success.

yep, I want to center it in the ImageView, I cannot use the center of the ImageView, and if I try to calculate the margin (imageviewsize-drawablesize)/2 it does not work — Lisa Anne, Jan 16 '16 at 13:52
`I need to put the image at the center` - so you have to: `use the center of the ImageView` — pskink, Jan 16 '16 at 14:29
using simply the center of the imageview, will translate the image to the center of the imageview no matter what is the size of the image shown — Lisa Anne, Jan 16 '16 at 14:32
of course `m.mapRect(out, src);` is for verification only (last 4 lines) — pskink, Jan 16 '16 at 14:48

Levon · Accepted Answer · 2016-01-17T11:20:16.553

All you have to do is to find new x and y coordinates where to place the image and then translate the matrix, so the image moves to the center of the ImageView. Your entire scaleImage method can look something like this:

private void scaleImage(float scaleFactor, float focusX, float focusY) {
    Matrix displayMatrix = new Matrix();
    Matrix matrix = imageView.getImageMatrix();

    float x = (imageView.getWidth() - imageView.getDrawable().getIntrinsicWidth() * scaleFactor) / 2;
    float y = (imageView.getHeight() - imageView.getDrawable().getIntrinsicHeight() * scaleFactor) / 2;

    matrix.postScale(scaleFactor, scaleFactor);
    matrix.postTranslate(x, y);

    displayMatrix.set(matrix);
    imageView.setImageMatrix(displayMatrix);
}

score 0 · Answer 2 · answered Jan 16 '16 at 14:08

Try my code hope will help you:

 private void scaleImage(ImageView view, int boundBoxInDp)
{ 
 // Get the ImageView and its bitmap
 Drawable drawing = view.getDrawable();
 Bitmap bitmap = ((BitmapDrawable)drawing).getBitmap();

 // Get current dimensions
 int width = bitmap.getWidth();
 int height = bitmap.getHeight();

 // Determine how much to scale: the dimension requiring less scaling is
 // closer to the its side. This way the image always stays inside your
 // bounding box AND either x/y axis touches it.
 float xScale = ((float) boundBoxInDp) / width;
 float yScale = ((float) boundBoxInDp) / height;
 float scale = (xScale <= yScale) ? xScale : yScale;

// Create a matrix for the scaling and add the scaling data
 Matrix matrix = new Matrix();
 matrix.postScale(scale, scale);

  // Create a new bitmap and convert it to a format understood by the ImageView
  Bitmap scaledBitmap = Bitmap.createBitmap(bitmap, 0, 0, width, height, matrix, true);
  BitmapDrawable result = new BitmapDrawable(scaledBitmap);
  width = scaledBitmap.getWidth();
  height = scaledBitmap.getHeight();

 // Apply the scaled bitmap
 view.setImageDrawable(result);

 // Now change ImageView's dimensions to match the scaled image
 LinearLayout.LayoutParams params (LinearLayout.LayoutParams)view.getLayoutParams();
 params.width = width;
 params.height = height;
 view.setLayoutParams(params);
}

Hi Rohit, thanks, that will definitely work, the problem is that decoding the bitmap takes way too much time, it's not good for image editing applications :-((( — Lisa Anne, Jan 16 '16 at 14:19

Android ImageView scale image and center

2 Answers2