An overscan is not a demo effect but a technique or better said a « trick » developed and used by coders to display things beyond the theorically limited window size of the Atari ST. To all of you, especially the young ones, it may sound strange but yes, computers from the 80s could not display pictures on the full surface of the monitor !

The Atari ST for instance could display pictures into a 320 pixel wide and  200 pixel high window. Beyond these limits the screen was nothing but… black. That is the reason why, in my humble opinion, these limits were called  « borders »  as they were some sort of « unbreakable » boundaries.

Là vous voyez bien les "borders" c'est à dire les bandes noires autour de l'image.
You cannot miss the « borders » that is to say the black parts of the screen all around the 320×200 displayed window…

You can take the picture above as a witness and understand that sometimes our screen seemed a bit small. So we thought until the overscan suddenly widened our viewpoint ! Each coder secretly kept his trick to manage such « magic » and display images in the left then right border. Later on they managed to display images either in the upper or lower border as well but let’s first have a look at an expanded screen.

Let’s open the left and right border ! Things seem so different at once ! Better than the 1st screenshot, isn’t it ? Taken from the huge Phaleon Gigademo by NeXT (1992).

This overscan technique can be used with « moving » screens as above but also to display pictures (still screens) such as below :

Panorama
The original picture size on the left is 320 pixels by 200 while the expanded version size is 400 pixels by 277. This superb picture was painted by Modmate of democrew Checkpoint.

This example shows how much space is added, impressive isn’t it ? By the way I need to apologize : first because some screenshots on my blog are crippled so that you won’t always see the borders and secondly because I cannot give you technical explanations about overscan. Coders could tell you but I am not a coder…

Anyway in this picture you can notice that not only the left and right borders are removed but also the upper and lower ones. This is then called a fullscreen effect as the whole space available on screen is used.

To make things clear, an  overscan is a screen with at least  2 borders removed be it horizontal or vertical ones. When all borders are removed we call it a fullscreen and as you can guess it is harder to remove all of them. 🙂

This is a fullscreen picture. Go back to the first screenshot in this article and do the maths ! Taken from the 1994  Japtro demo by Holocaust.
Full of stars and fullscreen ! Taken from the 1994 Japtro demo by Holocaust.

Since I am not familiar with the early Atari ST demos from the 80s when the first attempts at breaking the borders were to be seen, I can only recommend you pay a visit to this cool website to know more about the history of overscan demos !

Like I said earlier screenshots are not always suitable that is why I invite you to watch some videos like this one taken from the 2009 Suretrip II demo by Checkpoint. Here you cannot miss the moment when the screen goes bigger and wider :

In the « old » days, understand the late 80s and the 90s, there were not so many overscan screens and even fewer fullscreens well at least where there were, they were seen as technical treats. However today’s demos have brought so many progresses that expanded screens are almost « everyday’s bread » (not meaning in any way that anyone can do it tho). The following demo is a stunning example of a full show in  fullscreen. Please take a seat, relax and enjoy the show we are given by Dead Hackers Society with this 2014 SNDH 4.4 Update.

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