Contrast Ratio Explained

Contrast Ratio Overview

Simply put, a contrast ratio is a measure of the difference between two colors a display, or in this case a TV, can produce. The two colors are white and black, or for arguments sake, the lightest and darkest colors a TV can produce as many might argue the colors are not a true representation of white or black. With this in mind it is important to remember, that there is no official way to measure contrast ratio. Only preferences within the industry. This explains why one TV you look at may have a 1,000,000:1 contrast ratio, but another TV for the same price will only have a 500,000:1 contrast ratio. With that being said, I’ve listed some types of contrast ratio below to show how many different versions one company may use compared to another. Often times a manufacturers will list the best one over the most accurate one. Granted they are allowed to do this as it is something they did measure.

 contrast-ratio-trt
What is it: Brightness difference between lighter (white) and darker (black).
Why it matters: A base-line for picture quality.
When it matters: Especially when watching dark images or scenes.

Types of Contrast Ratios

Color Contrast A metric for color contrast often used in the electronic displays field is the color difference.
Full-Screen Contrast The active area of the display screen is often completely set to one of the optical states for which the contrast is to be determined, e.g. completely white (R=G=B=100%) and completely black (R=G=B=0%).
Full-Swing Contrast When one test pattern comprises the completely bright state (full-white, R=G=B=100%) and the other one the completely dark state(full-black, R=G=B=0%) the resulting contrast is called full-swing contrast.
Static Contrast When luminance and/or chromaticity are measured before the optical response has settled to a stable steady state, some kind of transient contrast has been measured instead of the static contrast.
Transient Contrast When the image content is changing rapidly, preventing a stable constrast.
Dynamic Contrast A technique for expanding the contrast of LCD-screens.
Dark-Room Contrast The dark state of the display under test must not be corrupted by light from the surroundings.
Ambient Contrast The contrast that can be experienced or measured in the presence of ambient illumination is shortly called ambient contrast.
Concurrent Contrast When a test pattern is displayed that contains areas with different luminance and/or chromaticity. (Checkerboard)
Successive Contrast When a contrast is established between two optical states that are perceived or measured one after the other, this contrast is called successive contrast.

Calculate Contrast Ratio

Many manufacturers will be most likely to use the Full On/Full Off method of measuring a contrast ratio. This will measure the dynamic contrast ratio of the display of TV, but unless performed in a room under ideal conditions will lead to some inaccurate measurements. Essentially, what takes place is equal amount of light will reflect or bounce from the dipslay into the viewing area. When reflected back, the light is read in lighter (white) and darker (black) measurements. Very simple and straight forward. Though, this doesn’t not best represent a viewing experience that you would have yourself.

Another way would be the American National Standards Institute method or ANSI method. This is the method I prefer to use as it best represents how you will be viewing your TV at a proper viewing distance and viewing angle. A checkerboard image is given to the display or TV to produce. This is important to remember because instead of testing the reflected light that bounces, the lighter (white) and darker (black) colors are measured simultaneously. This makes for a more realistic contrast ratio representation, but just like the Full On/ Full Off method,  the viewing area must be unchanged. Even more so as the measurement is simultaneously and the incoming ambient light must be unchanged.

Dynamic Contrast Ratio Explained

Dynamic contrast ratio (DC) or Advanced contrast ratio (ACR) is much more recent than the other types of contrast ratios that you can measure. To further explain why dynamic contrast ratio is important, you’ll need to understand why it is different.

When a need for a darker image or scenes is made known to the TV, the TV will underpower the backlight lamp that helps produce the colors and intensity of those colors. At the same time this is being done the transmission through the LCD panel is amplified by the TV. This in turn will help the TV to produce a contrast ratio more closely resembling a static contrast ratio. This is beneficial when viewing the display or TV in a darker room, but the downfall is that a dark image or scene with a bright image in the middle may have that bright image overexposed. That will lead to a blooming effect and make the picture look sub-par compared to its average performance.

Before Dynamic Contrast Ratio After  Dynamic Contrast Ratio
   

Now why is this important? The dynamic contrast ratio is often times a much higher number than the static contrast ratio. So often times manufacturers will advertise the dynamic contrast ratio that is 1,000,000:1 over a static that is 10,000:1, but in reality they both produce visually similar images and scenes at the same level of brightness.

Static Contrast Ratio Explained

When marketing or advertising a TV’s contrast ratio, the TV is always measured under the most ideal conditions in the factory. This means the display or TV will be surrounded by darkness with no incoming light. Often times over and over again so the manufacturers can market and advertise the highest possible number for the contrast ratio.

Though in most situations, such as yours while you’re reading this article, the viewing experience is much different. You may have your windows open or perhaps you need to get those blinds fixed. Either way a little bit of light gets in and that changes the contrast ratio drastically. That’s why even though a movie projector with a contrast ratio of around 500:1 looks amazing. No incoming light and surrounded by darkness. To expand on that, mant LCD monitors for computers have a contrast ratio around 1000:1 while a good number for a TV is around 2900-3000:1.

Conclusion

Contrast ratio is a measurement of the difference between two colors. The brightest and darkest. Though, there are many ways to measure this, the most common are Dynamic Contrast Ratio (DC) with the Full On/ Full Off method and the Static Contrast Ratio with the ANSI method which is my preferred method of measuring contrast ratios.

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