Resize a bitmap respecting the aspect radio. I use a custom transformations with Picasso library. This transformation calculate the new dimension of the bitmap scaling it to fit a specific width or height that we pass as a parameter (usually the biggest size of the imageView where we wanna set the bitmap).

ScaleToFitWHTransformation.java

public class ScaleToFitWidthHeightTransform implements Transformation {

        private int mSize;
        private boolean isHeightScale;

        public ScaleToFitWidthHeightTransform(int size, boolean isHeightScale){
            mSize =size;
            this.isHeightScale = isHeightScale;
        }

        @Override
        public Bitmap transform(Bitmap source) {
            float scale;
            int newSize;
            Bitmap scaleBitmap;
            if(isHeightScale){
                scale = (float) mSize / source.getHeight();
                newSize = Math.round(source.getWidth() * scale);
                scaleBitmap= Bitmap.createScaledBitmap(source, newSize, mSize, true);
            }else{
                scale = (float) mSize / source.getWidth();
                newSize = Math.round(source.getHeight() * scale);
                scaleBitmap = Bitmap.createScaledBitmap(source,  mSize,newSize, true);
            }

            if (scaleBitmap != source) {
                source.recycle();
            }

            return scaleBitmap;

        }

        @Override
        public String key() {
            return "scaleRespectRatio" + mSize + isHeightScale;
        }
    }