ScaleTransformation.java

import android.graphics.Bitmap;

import com.squareup.picasso.Transformation;

public class ScaleTransformation implements Transformation {
    private final int baseSize;

    /**
     * @param baseSize px
     */
    public ScaleTransformation(int baseSize) {
        this.baseSize = baseSize;
    }

    @Override
    public Bitmap transform(Bitmap source) {
        int size = Math.min(source.getWidth(), source.getHeight());
        if (size <= baseSize) {
            return source;
        }

        float scale = (float)baseSize / (float)size;
        int width = (int) (source.getWidth() * scale);
        int height = (int) (source.getHeight() * scale);
        if (width <= 0 || height <= 0) {
            return source;
        }

        Bitmap result = Bitmap.createScaledBitmap(source, width, height, true);
        if (result != source) {
            source.recycle();
        }
        return result;
    }

    @Override
    public String key() {
        return "square" + baseSize;
    }
}