PROJECTION KNOWLEDGE

Front and rear projection: Frontal from the front or effects from behind?

In the image synthesis process, a distinction is made between front and rear projection:

The intended use should always be analysed before selecting the right projection screen. There are films that can be used universally and projection films whose area of application is clearly defined.

Quality of the front projection

The quality of the front projection depends on the following factors:

• Reproduction quality
  

The quality of a front projection depends on the reproduction quality of the projector, which is influenced by the achievable luminous flux, the contrast capability and the projection ratio.

• Ambient light
  

The higher the scattered light, the more of it falls on the screen. This has a negative effect on the reproduction quality because the scattered light brightens the useful light and thus reduces the contrast of the reflected image - it appears less clear. For front projections, it can be useful to keep the brightness of the ambient light as low as possible in order to achieve good projection results.

• Stretch the projection surface as flat as possible
  

For optimum image quality, the projection screen should be stretched as flat as possible. Frame screens such as DECOFRAME or FULLWHITE offer the best results, but require a fixed installation. Alternatively, mobile systems such as MONOBLOX 64 or VARIO 64 are recommended. In the theatre sector, large projection surfaces are eyeleted and fitted with pockets for load tubes, while in the event sector, films are often stretched in truss frames.

• Colour of the projection surface
  

The colour of the screen influences the contrast and brightness of the projection. White projection surfaces such as GAMMALUX, SCENE or OPERA WEIẞ 2.2 reflect light well and are sufficient with average brightness. Grey screens such as the back of the GAMMALUX DUO offer better contrast, but require a brighter projector. A black back of the projection screen additionally improves the contrast. In home cinemas, black stage molleton is often used as a backing to avoid distracting reflections. Alternatively, light-proof projection screens such as GAMMALUX DUO, OPERA HIGH GAIN, SILVERBLACK or SCENE are suitable. Technical data sheets contain colour spectrograms for evaluating colour neutrality.

• Reflection behaviour of the screen surface
  

A suitable front projection film or screen should have a high reflective capacity and distribute the light evenly over the side viewing areas. It requires sufficient luminance and an even luminance distribution to avoid hotspots. The luminance factor, also known as gain, describes the efficiency of a projection surface compared to a defined white reference surface. The luminance is measured at different viewing angles, whereby it is highest when the projected light falls vertically onto the screen and the viewer is looking at the projection surface along the same axis. The further away the viewer is from the projection axis, the lower the luminance of the reflected light generally becomes.

Projection screens with format - it's the image size that counts!

The choice of the right screen format depends on the desired display format of the projection.

Square screen format (1:1)

A square screen format is preferably selected for the projection screen if an overhead projector is to be used.

Cinema or HDTV screen formats (16:9)

Cinema or HDTV screen formats are selected for projection screens that are to be used for showing films (DVD, Blu-Ray or TV programmes).

Video screen format (4:3)

A video screen format is ideally selected for a projection screen that is used to visualise data from the computer on the screen (e.g. for PowerPoint presentations).

Slide screen format (3:2)

A slide screen format enables a slide show without distracting white frames around the projected images. This is because an image with a black border has a higher image contrast in the subjective perception. For this reason, the images on the projection screen should fill the bright area of the projection screen as completely as possible.

Panorama format (2:1 / 3:1)

The panorama format is used for large screens such as a horizon screen for theatres, studios, trade fairs and events and is available in the form of the VARIO 64 [insert link to product] stretched screen for front projection.

WUXGA screen format (16:10)

The WUXGA screen format is particularly suitable for Full HD projection with 1,920 x 1,080 pixels.

The choice of screen size therefore depends on the size of the room and the viewing distance: even from the greatest distance, all details should still be easily recognisable. At a close viewing distance, the projected image should still be easy to see as a whole.

Maximum viewing distance = screen width x 6 - The width of the screen should be greater than 1/6 of the maximum viewing distance.

Smallest viewing distance = screen width x 1.5 - The minimum distance to the screen should not be less than 1.5 times the screen width.

If the screen wall is too large, the colour brilliance, contrast and image sharpness will suffer, as the projected image must be blown up accordingly by the projector. If the screen is too small, the transmitted images are razor-sharp, but the feeling of impressive visual film enjoyment that comes from watching a projection on a cinema screen is missing.

SCREENS: Special sizes