Yes, having a PGraphics that get() the current sketch's output is probably the best way to go for this.
And I am not sure what you mean by " but well..."...

Hm, the following with only one PGraphics reference in the List doesn't scale somehow:

1.         for (final PGraphics buffer : mBufferedImages) {
               try {
                   mLock.acquire();
                   buffer.scale(0.25f);
                   System.out.println(buffer.width);
                   mParent.image(buffer, 0, 0);
   //                mParent.translate(image.width / 2, image.height / 2);
               } catch (final InterruptedException exc) {
                   exc.printStackTrace();
               } finally {
                   mLock.release();
                   // LOGWRAPPER.debug("[draw()]: Available permits: " + mLock.availablePermits());
               }
           }
   

I just wanted to simply scale one buffer image and then extend the visualization to more than one small image, but the size of the buffer remains unchanged, which seems to be odd.

The "but well..." is because I would need some kind of different coordinate systems I think for a synchronized hover effect if the item remains in the following small multiple. For example to get the depth in a SunburstView I have the following method:

1.     /** Initialize rollover method. */
       private void rolloverInit() {
           mHitTestIndex = -1;
   
           final PVector mousePosition = getZoomer().getMouseCoord();
           mX = mousePosition.x - mParent.width / 2;
           mY = mousePosition.y - mParent.height / 2;
   
           mAngle = PApplet.atan2(mY - 0, mX - 0);
           final float radius = PApplet.dist(0, 0, mX, mY);
   
           if (mAngle < 0) {
               mAngle = PApplet.map(mAngle, -PConstants.PI, 0, PConstants.PI, PConstants.TWO_PI);
           } else {
               mAngle = PApplet.map(mAngle, 0, PConstants.PI, 0, PConstants.PI);
           }
           // Calc mouse depth with mouse radius ... transformation of calcEqualAreaRadius()
           mDepth = PApplet.floor(PApplet.pow(radius, 2) * (mDepthMax + 1) / PApplet.pow(getInitialRadius(), 2));
       }

which I suspect wouldn't work after scaling for small multiples ;-)!?

regards,
Johannes

" the size of the buffer remains unchanged, which seems to be odd."
Not odd. I can't see where you found that scale() could change the size of an image, even less in place.
scale() is like translate() and rotate(), it changes the system of coordinates, and thus affects how new graphic primitives will be drawn. An alternative to scale() is just to specify a dimension in the image() call.

And I am not sure to understand your issue, but perhaps pushMatrix() can help you.