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LED displays promise to change the way movie and television productions are created, but the effects are only as good as the video walls on which they’re shown. Those displays are constantly improving. Just a few decades ago the pixel pitch, or the distance between individual pixels in an LED display, was in the range of 12 mm, making them suitable primarily for viewing from a distance. Today, the pixel pitch of some displays is in the range of .6 mm or smaller, making them comparable in resolution to an LCD display. Although that shrinking pixel pitch has greatly improved the resolution of the displays it does create challenges that need to be overcome to make them suitable for video applications. Concerns that need to be addressed when using LED displays in video productions include:

 

Brightness

Adjustable screen brightness For different scenarios, the brightness of screen is needed to adjust to meet requirements.

 

Refresh rate

Refresh rate at high brightness – According to the “10 times refresh” theory, the refresh rate for high brightness LED displays needs to be more than 10 times the camera shutter speed for images taken by the camera to be free of lines and defects. A typical camera has a shutter speed of about 1/200 second, so the refresh rate of an LED display in a broadcast application needs to be greater than 2,000Hz or bright lines will appear in the image.

 

Most fine-pitch LED displays today use PWM-based driver chips, which have the characteristics that the refresh rate at low-grayscale levels is lower than that at high-grayscale levels. As a result, when showing a low-grayscale image on the LED screen black streaks appear on the picture taken by the camera, greatly affecting the visual experience.

 

Grayscale

The loss and discontinuity of pixel data at low grayscale levels greatly reduces the smoothness of images, causing them to appear unclear to viewers. There are two causes of this problem. The first is that the grayscale data of the video source is compressed. This leads to a loss of a certain amount of grayscale and is likely to cause blocky images. The second is that the grayscale output bit number of the LED display is too low. Therefore, the jump span of each level at low grayscale is too large, thereby causing discontinuity.

 

 

HDR

If the LED display has a higher grayscale output, such as 16-bits, it can decrease discontinuity problems and lead to a better visual performance. Viewers can see more details, especially under low brightness conditions. In addition, when the video source is HDR, an LED displays would perform better with 16-bit grayscale output and a higher refresh rate. This kind of opulent image quality will bring a photorealistic performance making it well suited for movie backdrop use.

 

 

Contrast

Insufficient contrast causes a loss of image detail and results in images without multiple layers, similar to a painting without depth and color.

Moire

Moiré patterns are large-scale interference patterns that can be produced in an image when an opaque ruled pattern with transparent gaps is overlaid on another similar (but not identical) pattern.

LED displays are notorious for using a great deal of energy and generating a large amount of heat that can drive up costs and shorten display life.

 

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