Zoom effect on certain screen area or sprite

[SpDizzy]

Hi all.
I was thinking about the possibility of implementing a zoom effect over an area of screen, either static background or sprite. I have seen such a similar effect on impressive Batman Forever Demoscene from Batman Group, as attached .gif image.
I was wondering if is possible to make the zoom-in effect over the window, or the zoom-in / zoom-out effect over the clown with no prerendered images at different sizes for each needed frame, I mean, doing some sort of calculations or altering CRTC registers.
Any ideas on how to archieve this? Is there any known method or best approach for that?
Thanks so much in advance, I really appreciate the support.

[Rhino]

Hi!The 3 fxs of the gif are 3 different techniques and there are many more, everything depends on the context where you want to apply it but, if you are curious, the zoomscroll source code is published in the BF thread at cpcrulez.

[SpDizzy]

Thanks so much for your response Alejandro, I really appreciate your time. I didn't knew zoomscroll source was published on BF thread. I'm really curious about zoom thecniques for a little project. In fact I'm really curious about all the magic behind the computer that gives me hours and hours of joy many years ago when was a child, and still do it today. Specific those game related, so my dream is to develop something playable on my own. You know, just a nostalgic trying to revive those times. Thanks again, your talent got me shocked. Waiting for pinball dreams!!