The resolution in the images of the giant screens

In this tribune, Mark Fernandez, director of Christie Iberia, analyzes what type of screens the market offers for domes and planetariums, and the benefits of projectors to provide an immersive experience, true to reality.

With 4K and 8K TV already in homes and 4K projectors running in standard cinemas, Is 4K the right resolution to ensure that unparalleled experience that giant screen exhibitors – such as domes and planetariums – need to attract viewers to their rooms??

When talking about performance, the simple use of the expression '4K resolution' can be totally simplistic, as it excludes other factors that affect the final resolution of the system and, consequently, to the image quality perceived by different viewers.

Those factors include:

• Critical aspect: No projector chipset for aspect ratios 1.43:1.
• Greater vertical viewing angles in domes: Good viewing angles up and down are required.
• Lens degradation: Projector optics can have a big impact on focus, clarity, sharpness and contrast.
• Screen: The finish of the screen surface and the perforations for the sound scatter the light and somehow degrade the perception of the resolution of the system by the viewer.
• Seating position: The location of the seat may affect the final perception of resolution or sharpness.
• Camera used in the filming of the film and the post-production process: Both factors affect the final resolution of the system.

How much resolution is sufficient?

The equivalent resolution of the film of 70 mm and 15 perforations is 18 to 36 accessible megapixels (on-screen). The minimum acceptable to replace the film is a few 22 megapixels. That level offers the viewer an experience minimally comparable to that of the film., regardless of the seat it occupies. 4K resolution (4.096 width x 2.160 high) is, simply, too low to ensure a good result.

Everyone knows that the resolution is much more decisive in the case of domes than in flat screens.

Stretching the number of pixels from a single 4K projector in a dome results in excessively large pixels, whose size will distract even the best placed viewer and which the spectators located on the sides will perceive even with a worse quality. It's about, In addition, of a resolution significantly lower than that of 70mm film and 15 Drilling.

Here's an example that explains why installations with multiple projectors look much sharper than installations with a single 4K projector.:

• Three 4K projectors in blending and portrait mode offer 5.700 pixels wide x 4096 pixels high, and a total of 22 accessible megapixels.
• A single 4K projector in landscape mode offers 4.096 pixels wide x 2.160 pixels high, and a total of 8,8 accessible megapixels.

Impact anamorphic lenses on images of giant screens

In the real world, it doesn't matter where we turn our heads, our visual acuity remains unchanged. In other words: the sharpness with which we perceive vertical lines, horizontals or angles do not change (vertical resolution = horizontal resolution).

If we want to reproduce what we see naturally, it is convenient to use square pixels, and not rectangular. To avoid distortions it is key that the shape of the pixels of the film capture corresponds exactly to that of the projected pixels.

Some cinema systems use anamorphic lenses (also called 'fisheye lenses') to stretch images of the projection. If we carry out that action in digital projectors with dmd of square pixels, those pixels lengthen, no longer squares on the screen. The result is the loss of uniformity in resolution., that will decrease in the direction of stretching.

That circumstance would indicate that systems that use standard non-anamorphic lenses and square pixels offer greater image fidelity than those that use anamorphic or fisheye lenses in domes..

In addition, whether the various projectors in a blended system use standard lenses, each of the lenses provides a more uniform resolution, a lower heat load, better depth of field and superior overall image quality than any anamorphic lens is capable of, by itself, to generate in a dome.

Conclusion

It is clear that the market for giant screens in domes and planetariums must improve its offer for, at least, keep pace with the commercial film market and attract audiences to their theaters.

Taking advantage of the possibilities offered by screens with multiple projectors to provide an immersive and sharp experience more true to reality could be one of the keys to providing the wow effect that audiences crave..

Mark Fernandez

Director of Christie for Spain and Portugal

 

 

 

 

 

 

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