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What is Projector Contrast?

The projector contrast describes the relationship between the very brightest and darkest images that the projector can produce. The contrast is expressed as a ratio of the brightest to the darkest parts of the image. 

There are two common ways of describing the projector contrast:

ANSI or Intra-scene Contrast - Describes the relationship when both brightest and darkest are reproduced simultaneously within the same image.

On/Off Contrast - Describes the relationship when only the brightest images are reproduced followed by the darkest parts in two separate images.

PJcontrast_1

Why is Projector Contrast Important?

An image with high contrast will always look better than an image with low contrast. In projection systems the limiting factor is almost always how dark the darkest parts of the image can be made. Increasing the contrast improves the shadow details and subtlety of the image. Low-contrast images tend to have a slightly grey haze to them that breaks the feeling of looking at reality on the screen!

PJ_Incorrect_Contrast
PJ_Correct_Contrast

How is the ANSI Contrast Calculated?

The Ansi contrast is found by measuring the brightest and darkest parts of the image using a checkerboard pattern. The pattern has 16 equal squares, 8 white and 8 black. Each of these is measured and then the average brightness of the white squares is divided by the average brightness of the black squares to produce the ANSI contrast.


Example - Calculating the ANSI Contrast
Average White Brightness (AWB) = 98.6 nits 
Average Black Brightness (ABB) = 0.15 nits

ANSI = AWB : ABB (simply AWB / ABB)
ANSI = 98.6 : 0.15 
ANSI = 657.3 : 1 (simply 98.6 / 0.15)

PJ_Cotrast_calculation

How is the On/Off Contrast Calculated?

The on/off contrast is found by measuring the brightness of a full white screen and then dividing that by the brightness of a full black screen.

Example - Calculating the On/Off Contrast
White Brightness (WB) = 98.6 nits 
Black Brightness (BB) = 0.03 nits

On/Off = WB : BB (simply AB / BB)
On/Off = 98.6 : 0.03 
On/Off = 3286.7 : 1 (simply 98.6 / 0.03)
PJ_Cotrast_calculation_on_off
PJ_Cotrast_calculation_on_off_white

Projector Contrast Considerations

Projector Contrast is very important to performance but can also be very difficult to quantify in the real world. It is important to understand these factors. On/Off contrast always appears higher than ANSI but does not reflect the reality of use.

  1. Does the projector specification mention ANS contrast or On/Off contrast? If no value is mentioned then assume On/Off.

  2. How light are the walls in the room? The light reflecting off these surfaces will elevate the black parts of the image reducing contrast.

  3. What colour is the screen surface? Grey screens lower the black level increasing the contrast.

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