The contrast ratio in projector measures the difference between the brightest and the darkest parts of a projection.
Contrast Ratio, Contrast Ratio Definition, Contrast Ratio Measurement, Contrast Ratio For Projector: Contrariwise to some beliefs, contrast ratio is not an intensity-based measure. It’s actually a measure of how dark or light the scene would appear if it were projected on a perfectly white screen that’s uniformly illuminated. The measurement is relative to the peak white point (the brightest part of your projection), sometimes called illuminance. In other words, exposure correlates with contrast ratio instead of luminance (brightness).
Contrast ratio is used to describe the difference between the sum of all light in a particular image and the darkest part of that image. The measurement is given in terms of the black level or minimum luminance that can be reproduced as well as the white level or maximum luminance that can be reproduced. This is usually calculated to two decimal places. The measurements are not absolute values, but relative to one another.
Also read: What is contrast ratio in projector?
High contrast ratio means dark blacks and bright whites, low contrast ratio means light blacks and dim whites; if you look at a bunch of TVs side by side, it’s easy to see which one has more distinct blacks (in this case, it’s likely to be the TV with higher contrast ratio).
Contrast ratio is not synonymous with dynamic range. Dynamic range is a measure of how much richer the blacks are relative to the whites in a scene compared to the maximum luminance that can be achieved by interlaced video. Contrast ratio was originally used for videoconferencing and measuring the contrast between computer screens that showed different color shades, which meant that monitor needed to support more colors than just 16 million (256 discrete grayscale) in order for real-time communication. If you look at a lot of monitors side by side, you can see which one has a wider range of colors because it renders them at higher luminance levels than those of other monitors.
Contrast ratio is an indicator of how much information can be displayed at different luminance levels. It is a useful metric for comparing projectors because it is easy to measure and it has been used for decades.
Read more: What is a good lumens for a projector?
What is a good contrast ratio for a projector?
The contrast ratio, or perceived difference in light output or luminance between two different areas – the projection area of a projector and the screen on which it projects – is an important piece of information to consider when buying a new projector. It can have significant effects on several factors that affect how humans perceive images displayed on a projection system, including:
Relevant reading: What is a good contrast ratio for a projector?
A good contrast ratio is one where the image will be clear and bright enough with little blurring or artifacts even at high frame rates. For the human eye, a contrast ratio of at least 1000:1 is usually considered sufficient. Contrast ratios for commercial projectors can range from 3000:1 to 80000:1 or higher.
The contrast ratio depends on both the projector and the screen. In some cases, it can be manipulated using electronics in the projector (via gamma corrections and digital gain) and/or dynamic optical properties of the screen (via iris effects).
Contrast ratios tend to decrease over time as lamps age, particularly for projectors that don’t have an automatic lamp fail safety feature. Just like a TV, a projector will start to “burn out” when its lamp runs at full brightness for too long. A burned-out lamp can’t be replaced and the LCD panels (if any) will quickly deteriorate. Projector lamps require replacement every 1–4 years depending on duty cycle and hours of utilization.
Projector Gamma Correction
Gamma Correction is the adjustment of brightness from the internal processor in order to display an image on a screen that better matches what you would see if projecting it onto a white wall.
You can adjust gamma correction by going into the settings menu of your projector, and choosing the Gamma.
Though many people recommend using a 2.2 gamma, this is not correct. It is recommended and started with a 2.2 gamma, but this can cause some problems on certain projectors, particularly those that are DLP based and use an older generation chip (DLP-3000).
The contrast ratio depends on the projector and screen.
For most projectors the best contrast ratio comes from either putting the projector directly in front of a white wall or ceiling, or placing it in front of a white screen.
The contrast ratio depends on which projector or screen you have as well as the distance from the projector to the projection surface and where you’re sitting to watch the movie/show. The contrast ratio will also vary based on the content being projected, and the image resolution that the projector is displaying. In general, with higher pixel density, brighter images will generally have better contrast ratios than lower pixel density images.
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For movies we recommend projector combinations with a longer throw, which means that the projector is closer to you. The shorter throw projectors can still be used for lower resolution video games or video presentations that are not as taxing on your eyesight or focus. If you are only using your projector to display movies, and you are sitting close enough to the screen that you will not have any of the above issues it should be fine.
Contrast ratios for projectors with lamp life under 1 year tend to drop steadily as the lamp ages. After 3 years the contrast ratio tends to stay constant, or a little higher than when new. Contrast ratios from 5 to 10 years old can drop as low as 1000:1 (for ultra high resolution screens) at some distance from center, while contrast ratios for projectors that haven’t burned out yet can be as high as 10000:1 (or more) at close viewing distances using an iris aperture of 0 dpt. Longer throw projectors (those that are placed further away from the screen) also tend to have higher contrast ratios. Due to limitations of current LCD technology, no projector is able to reproduce black levels approaching 0.0 dpt (dynamic contrast). Even though today’s LCD projectors can produce over 100000:1 contrast ratio at 0 dpt, the black levels will still be higher than when using a projection surface with a non-zero dynamic range.
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Using these techniques can help you achieve or exceed 1000:1 maximum contrast ratio regardless of what screen you are using. Some people find that this is too high a contrast ratio. To achieve the 1000:1 maximum contrast ratio, you need to make sure you have the latest projector firmware.
Contrast ratios are measured differently among manufacturers versus users because users are measuring it at different distances from screen and projector-to-screen distance, which usually results in different contrast ratios than what is specified in the manual or website specifications for that product.
When a large amount of white is in the image, the contrast ratio will be lower on lower-contrast screens and higher on higher-contrast screens. This is due to the physics behind how light reflects off white surfaces versus dark surfaces. For an equiluminance screen, the contrast ratio is proportional to the square root of twice the reflectance (1 minus R) of the surface, where R is the reflectance of that surface.
The reflectances are taken from published data for each type of screen material and are only representative values. White is assumed for both surface 1 and 2 (the projection screen). This formula assumes that we are using an equiluminance screen material. The results will vary depending on how bright the white is on the screen and the distance of projection surface from the screen, and also other variables like angle from centerline.
The below measurements were done for a standard 16:9 ratio image (width is 1920 pixels) with a projected distance of 1.85 m from the projector to screen surface at center. The greater distance reduces contrast ratio, while greater brightness increases it.
The above table is for a white image on a dark “flat” 2D surface. If the image is non-white then the contrast ratio will be significantly lower. Additionally, if there were an angle between the projector axis and the screen surface, or if a “haze” layer was present on either of them, or any other factors that affect how light reflects off surfaces, then we would also see a large difference in contrast. Using a matte white surface with no haze layer improves contrast ratio as well.