How close do you want to be?

From 300M back adding more pixels would be wasted.

From 1M back it would be a great idea to use more pixels.

Top selling HD projectors are here

The human eye can see around 300 dots per inch.

You already know that the further back you are, the harder it is to make out the dots.

One example is a bill board usually printed at between 2 and 100dpi. This is why most sccanning is done between 200 and 600 DPI.

(DPI = Dots Per Inch and Pixels per inch in this review can be interchanged)

One big TV!

The pictures in this review feature a 9M display screen which has 2 pixels per inch.

Using an outdoor display seemed a better idea than taking pictures of a bill board because you get to see that brightness is often a key element in your viewing, unless you've a TOTALLY dark room.

On a bright day or a room with a fair amount of light all the contrast ratio and DPI in the world won't take the place of brightness or ANSI lumens.

Can you see the quality?

From 100M you can't see the dots on a bill board. Most people can't easily tell if they are watching an 800 x 600 projector or 1280 x 720 pixel model if they are say 5-6M back from a 2M wide screen especially in terms of detail.

MAN SIZED PIXELS!

We also take the same line with exzagerated contrast ratio claims, we've written a page on the CR subject too.

A 720P HD projector like the SANYO PLV Z5 using a 100 inch (2.2M) screen has twice the information per inch as the highest digital cinema standard (4K) and 4 times the current 2K standard.

High Definition

Using the highest 1080i standard for High Definition in Australia below is a charts relate to a projected image, 100 inches diagonal in size and a 40 inch TV.

Note is you should sit at least  twice as far back as the image is wide. This rule of thumb is generally accepted and has been our experience. This applies to TV's too.

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To see the most detail in a movie we'd say 2M is the closest you would ever want to sit from a 100 inch wide screen (100 inch is about 2.2M wide) it's not recommended but if it's your thing there is only one projector series to choose and that's the Panasonic AE700/AE900 due to their smooth screen technology.

From normal viewing distances the "Smooth Screen" has no advantage over say a Sanyo Z2, in fact the image won't be quite be as sharp.

In one line..

Based on 20/20 vision, every time you double the viewing distance you only require 1/2 the resolution for the image to look the same.

Projector

Screen Size (Inch D)	Distance Back (M)	Pixels Needed*
100	2	1080 x 1920 = 22PPI
100	4	540 x 960 = 11PPI
100	8	270 x 480 = 6PPI

*To look approximately the same at double the distance. PPI = Pixels Per Inch

To see the most detail on a 40 inch HD-TV, 2M is the closest you would want to sit to the screen. The tables ring true with our real life demonstrations. Note home 720P projectors are 15PPI on a 100 inch screen.

Screen Size (Inch D)	Distance Back (M)	Pixels Needed*
40	2	1080 x 1920
40	4	540 x 960
40	8	270 x 480
40	16	360 x 640

What does "Real" commercial digital cinema use?

Digital cinema currently uses standards known as 2K (2048 x 1080) 12 bit, 24FPS, with the aim to have 4K (4096 x 2160 pixels) as the ultimate standard.

4K is requirement for a 50-90 foot screen. Smaller venues use as little as 1280x1024 pixels.

Pixel size used in commercial cinema

Project a 2K image on a screen that's 15m/50 feet wide and each pixel is 15000/2048 = 7.3 mm wide. (3.5PPI) Using 4K each pixel is 3.6 mm wide. (7PPI).

What's can we have at home now?

Using a 2.2M wide screen (100 inch) and a 720P projector if we try the same formula for pixel size as used above (2200/1280) you end up with 15PPI and a pixel size 1.7mm which is half the size and has twice the information per CM as the highest digital cinema standard (4K) and 4 times the current 2K standard.

Put another way you could project an image 4M wide and still have more dots/pixels per CM than the 4K systems costing $100,000 ++

HD or SD?

The point of this review is to dispel the myth that you must have  HD/High Definition.

All else being equal get Hi-Def, however if the cost of the equipment is taken into consideration along with the intended use, it's not always a must have.

Foxtel is SD (AKA HQ), not HD.

Steven Brown
AIM Digital Imaging

October 2005
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