Welcome to ‘Kagoo Explains’ - a series of short articles de-mystifying some of the confusing terminology used to describe tech. This week we’re looking at contrast ratio in screens and projectors, and we’ll explain exactly how it can make your movies and games look better!
Contrast ratio is one of those technologies that gets a lot of breathless praise in the bullet-points of new projectors, televisions and PC monitors - words like ‘infinite contrast’ and ‘deep blacks’ sound impressive, but don’t really explain the core concept. At its most basic, contrast ratio is a measurement of the difference between the darkest and brightest colours that the screen can create in a single image. So a TV with a very high contrast ratio will be able to create both bright whites and extremely dark blacks in the same scene.
This is normally expressed as a ratio - so on a screen with a ratio of 500:1, the brightest part of an image will be 500 times brighter than the darkest part of the image. The higher the ratio, the better the contrast.
So why is contrast ratio important? It’s all about the detail and quality of the picture. The higher the contrast ratio, the more shades of light and dark can be displayed. This will make the difference between seeing the image as it was shot, or seeing a washed-out image that looks more grey than black.
Imagine you have a movie scene that takes place in a very dark room. With a low contrast ratio, the black shades are lighter, meaning there is little differentiation between different shades. This means that subtle details will end up getting lost, and everything looks a uniform black colour. However with a high contrast ratio television, there will be a stronger differentiation between all the different shades in the dark room, meaning you can pick up all the small subtle differences. Very important for film noir or horror movies!
Another example: video games benefit a lot from a strong contrast ratio. Seeing all the details of a game at night may make the difference between victory and being jumped by an unseen enemy!
Contrast ratio is not just uniform across a screen - it can vary largely from section to section. This is because of the way display technology works - an LED backlight shining through coloured filters and shutters (pixels) to achieve the desired image. A single LED is responsible for shining light through multiple pixels, which unfortunately means that if that particular section requires both black and bright colour (i.e - the edges of a flashlight beam in a dark room), some light will inadvertently bleed through the black filter, lightening it and turning it more grey than black.
This is why OLED TVs advertise such high contrast - they don’t use an LED backlight, since each pixel gives off light that can be independently turned on and off. Therefore there is no worry about light bleeding into the black areas of the screen - allowing for blacks that are as deep as can be.
You will sometimes see OLED TVs marketed as having ‘Infinite Contrast’ - it’s not quite as powerful as that name makes it sound, but they do have a very high contrast ratio indeed!
Finally, let’s talk about projectors. While TVs and PC monitors look better with higher contrast ratios, this isn’t always the case with projectors - especially ones that are placed in rooms with a lot of ambient light, or outside. Since images have a long way to travel to the display screen, the light in the room can make a very large difference to the final projected image. Even a small amount of light can lighten the screen significantly, meaning that all your deep blacks and small details are swallowed again and can’t be seen.
Therefore to allow your contrast ratio to work properly with a projector, you’ll need to remove as much light as possible - dim the lights, cover the windows, etc. However this isn’t always possible - especially if you’re trying to project outside. In these situations, you may actually find that a *lower* contrast ratio will work better. This is because a lower-contrast ‘grey’ black will be more easily visible in strong light than a high-contrast ‘black’ black. Most important is brightness though - a lower contrast ratio, higher brightness projector will work best outdoors, while a lower brightness, higher contrast ratio projector is best for indoor projecting.