Creating the IMAX Experience at Home

Introduction

When we built our current home, and with it my brand new cinema, we initially only put a 100″ 16:9 screen in. I know! Why even bother with projection with a screen that small unless you have a teeny tiny room?! Well, that screen was only installed for about a month before changing it to a massive 125″ CinemaScope.

For comparison, to be able to project widescreen movies at the same size on a 16:9 screen, you would need a 135″ 16:9 screen, which is pretty massive for a room with only 4.5m of depth.

The reason I went with 125″ CinemaScope was because 16:9 movies would still be 100″ on the screen when projected, while widescreen movies with fill the whole screen.

Projection at a Normal Multiplex

This is what we call equal image height projection, and it actually mimics what is done in a normal cinema: only the width of the image changes, not its height.

Also, when I said those movies were in 16:9 aspect ratio, I was not telling the truth. There is no 16:9 projection at a cinema: the closest aspect ratio is 1.85:1. When shown on a 16:9 screen, there are very small black bars on the top and bottom of the image.

Since people don’t generally notice this, especially on a TV, they think the movie is in 16:9 or full-frame. This isn’t the case. Only TV shows utilise the full 16:9 aspect ratio. Or is that the full truth? We’ll find out in a moment.

If we wanted to emulate a proper multiplex, we would have to have a CinemaScope screen (in orange above) and simply change the image so it always has the same height, like the illustration below. (Please note that 2.4:1 and 2.39:1 are close enough that we tend to treat them the same way.)

Optionally, we could have curtains to mask off the left and right side of the image. But since the projector isn’t throwing light onto that part of the screen, as long as we have a room with black walls and ceiling, those parts of the screen should not lit up from in-room reflections.

Projection at IMAX

Now when I said that only TV shows are shown in 16:9 aspect ratio on home media or streaming, I again lied to you. The IMAX aspect ratio is so close to 16:9, that IMAX movies will be transferred with a full 16:9 frame onto home media. However, and here is the massive catch that most people don’t understand: the IMAX aspect ratio isn’t 16:9 as shown in the previous illustration.

The IMAX aspect ratio is like the 2.39:1 (or 2.4:1) aspect ratio in terms of its width, but the top and bottom portions of the frame are restored (called open matte). In the illustration below, the CinemaScope (2.4:1) aspect ratio is the yellow box. While the red box illustrates what the IMAX aspect ratio would look like. Except, when transferring to home release, both will have the same width, only the image is filled in where the black bars would be on a 16:9 screen using the red portion of the frame.

This means two things:

1. IMAX movies generally alternate between CinemaScope and full-frame IMAX aspect ratios with the black bars appearing and disappearing. Although some movies might run full-length if they were shot with IMAX cameras all the way, but this is rare.
2. When shown in a normal multiplex, the top and bottom portions of the frame are cut off for the IMAX scenes and only the CinemaScope portion is shown. This is why the director will have guides on the IMAX cameras for both aspect ratios so that the shots can be framed correctly for both types of projection.

Projecting IMAX at Home

After having moved to a 125″ CinemaScope screen, I started to appreciate the idea of projecting movies according to their commercial cinema aspect ratios and relative sizes with equal image height projection.

However, I still wasn’t happy: 1.85:1 movies could be projected correctly, but IMAX movies had to have the top and bottom portions cut off. While serious home cinema projectors allow you to electronically mask the top and bottom of the screen for exactly such scenarios, I wanted to have the proper IMAX experience.

So I got rid of the screen and started painting different aspect ratio screens on the wall over the course of a year. Out of all the aspect ratios 2:1 is what I think would be the best match for home projection with the least hassle for the following reasons:

1. IMAX movies can have some of their extra information shown (not all)
2. CinemaScope movies would have minimised black bars
3. 16:9 movies would have some black bars to the sides but this is the price you pay for larger CinemaScope and IMAX projection

However, this is of course, not proper IMAX yet. During my time playing with different aspect ratios, I introduced a top masking system using a custom-order roller blind with non-reflecting black material and velvet for the bottom rail. This allowed masking the top of the screen for widescreen projection, turning the screen into CinemaScope.

It was time to get another commercial screen and I decided that due to the top masking working so well, I would get a larger 16:9 screen (settled on 125″ 16:9) so that all aspect ratios can be shown at their correct size:

1. IMAX movies can be shown full-screen
2. CinemaScope movies would be shown at the full width, moved to the bottom of the screen and masked with the top masking system
3. 1.85:1 movies and 16:9 TV shows (and similar aspect ratios) would have the top mask applied to make them the same height as CinemaScope movies with black bars at the left and right

This is really the only way to create the full IMAX experience at home, and I am more than delighted with the result. The next step will be to introduce a left and right masking system for content with black bars on the sides, likely using black velvet curtains with in-built rods or panels for accurate masking. However, since the room is now much like a black cave, those black bars aren’t really noticeable.

Other Considerations

When mounting a larger 16:9 screen, you need to make sure that all rows will have comfortable viewing regardless of the aspect ratio shown. Generally, THX recommends that eye level should be 1/3 of the screen height from the bottom. While it’s ok for the eye-level to go above this – such as 1/2 screen height, you should aim not to go below this as much as possible.

This may mean mounting the projection screen a lot closer to the ground than you normally would, and having the speakers behind the screen and equipment on another wall.

Alternative Option

An alternative, halfway option is to project IMAX content like CinemaScope content, but only electronically masking the bottom portion of the screen while opening up the top portion with the physical mask. This way the widescreen portions of the movie are shown at the correct – and possibly more comfortable height depending on your screen’s height – while IMAX scenes would open up and extend the top portion of the screen.

This option might also be more suitable for movies that are mainly in widescreen with only a couple of scenes in the IMAX aspect ratio and where both top and bottom black bars might be more distracting for most of the movie.

Conclusion

While we didn’t quite achieve all our design goals 100% in our home cinema for now, the rebuild has gotten us there 90%.

We can now show IMAX movies in their full glory with all the speakers behind a large-format screen.

In the near future, we may build in the front subs behind the screen as well, so the screen can be lowered even further to inch even closer to reference-level viewing.