RELATION BETWEEN: REFRESH RATE /
DRIVER / GRAYSCALE / SCAN FOR
VIRTUAL PRODUCTION LED SCREEN
WALL DISPLAY
Introduction to scan
and driving mode

Scanning Drive or Multiplexing or Scan type is the number of LED pixels that one Driver IC can connect to.

Each LED pixel is connected to one pin of the driver IC on the PCB board.

The more driver ICs we have on a PCB the lower the scan type.

Most suppliers will have 1/2, 1/4, 1/8, 1/16 and 1/32 1/48 scan types.

Scan and time multiplex are the same.

The scan number is the number of drivers required on a PCB board design to light up the pixel pitch:

The scan design is impacted directly by:

Each drive IC has 16 pins and can drive 16 LED chips maximum. Static drive mode means all the LEDs on the LED module can driven by IC at once, as shown in the following image

1/12 scan mode, means 1/12 LEDs on the module are driven by IC at one time, and next time there are other 1/12 LEDs that are driven.

1/6 scan mode, means 1/6 LEDs on the module are driven by IC at one time, and next time there are other 1/6 LEDs that are driven.

HDR-
OPTIMIZED

Refresh Rate

3840Hz

Grayscale

16-bit

SCAN NUMBERS

325

FRAME RATE

@ 60 FPS

@ 120 FPS

A high scan drive can reduce brightness of the LED screen and in most cases suppliers can use higher scans on higher resolution screens to compensate for brightness to be more cost effective.

Most high scanning Drives can be used on indoor LED screens as high performance of the screen is not an absolute requirement. Brightness is not an issue and you won’t have to compensate when there is not enough space for the PCB.

What is a scan
design?
Explanation the different between a scan design fine pitch LED display (Under 2.5mm) and standard LED display

A fine pitch display must accommodate more elements within the same unit area than a large pitch display, and the front of the module must contain even more LEDs.

Taking a P2.5 design with the LED and driver IC on the same side as an example:

One square meter module
must accommodate 160,000
SMD

The back of the module must have elements such as driver ICs and current setting resistors.

A static driver design would require 30,000 16-channel driver ICs and 30,000 current setting resistors

That will lead to an increased number of PCB layers, and increased cost are taken into consideration

This is where a time-multiplexing (scan) design is essential.

A time-multiplexing design makes use of a single driver IC to turn on more LEDs, saving space on the PCB board and optimizing the budget and driver IC’s layout.

However, under premises of high image quality, there is a trade-off between high grayscale and high scan rate. Because of this, the smaller the pitch, the greater the number of time-multiplexing in the design. P2.5 displays generally adopt a 1:16 time-multiplexing design, and 2 mm displays and below adopt time-multiplexing above 1:16.

Driver
mode
The lower the scan rate the better
the performance and the
more expensive it will be driver mode

Scanning Drive or Multiplexing is one of the methods of the LED module design. Its about the amount of LEDs that are connected with ONE chip leg.

There are design techniques that will make it possible to connect more LEDs on ONE chip leg. Most suppliers will have 1/2, 1/4, 1/8, 1/16 and 1/32 scan.

Scanning Drive will reduce brightness of the led screen and in most cases they will use it on a higher resolution for
brightness
compensation.
BRIGHTNESS

The higher the scan the more LED pixels one driver needs to light at once.

For each LED screen:

Static scan will double the brightness of 1/2 scan, and 1/4 scan will double brightness of 1/8 scan

However if brightness is not an absolute requirement, there are ways to lower the brightness by experimenting with the software.

REFRESH RATE
POWER
CONSUMPTION

the higher the scan, the higher the power consumption. This is an applicable multiple formula, for example 1/5 scan is double the power consumption of 1/10 scan. It is also restricted by the current. In the future, factories may reduce current and reduce power and brightness.

Side effects
of reducing scan

While a time-multiplexing design reduces the layout area and number of elements that must be used on the PCB board, it also impacts:

Therefore, it’s very important to choose a reasonable scan mode for the LED screen. It needs to be based on the brightness, power consumption, refresh rate and cost – not simply the higher the better.

In a time-multiplexing design, after the first row of LEDs is lit, the second row of LEDs is then lit, and so on. After the the final row is lit, scanning then returns to the first row.

Relation between scan and refresh rates

The refresh rate is the number of times per second (written in hertz, or Hz) a screen refreshes its image. When the number of scan lines is doubled, the time needed to light up all LEDs will also double and the refresh rate will be halved.

This means that the greater the number of time-multiplexing in a design, the more challenging it is to achieve a high refresh rate.

Usually lowering the scan rate will lower the refresh rate and vice versa. The refresh rate also depends on PCB design, however, and the type of driver IC.

The use of a driver IC with an embedded SRAM can increase the refresh rate by shortening the time transmitting grayscale data. If a driver IC supports GCLK multiplier technology, the refresh rate will need to be doubled again.

Grayscale & Bits

Grayscale indicates how many intensity levels from the darkest to the brightest can be displayed on an LED display.

You have probably seen this before on the parameters of your LED manufacturer – ‘grayscale = 12bit, 14bit, 16bit, etc ‘, but do you really understand what this is?

Generally speaking, the higher bits, the more colors you have. This means you have better effects and a richer content quality – like how 16bit is better than 14bit. This means the cost of your LED video wall will be higher for VP.

Higher grayscale allows more color changes in color images, so you can have a more natural color transition, more image details, and a higher quality of display effects can be delivered.

Contrast definition enables us to distinguish the content of an image regardless of the brightness of that image

Contrast is the difference between 2 images or 2 image components. This is the difference between the brightest, white, and the darkest, black.

But the truth is the gray level also depends on the number

The details for each bits:

1-bit processing system,

that is 2, (2 of the 1th power level grayscale), this means we can only set up two kinds of brightness, from black to white.

2-bit processing system,

that is 4, (2 of the 2th power level grayscale), this means we can set up four kinds of brightness, changes from black to white.

3-bit processing system,

that is 16, (4 of the 2th power level grayscale), this means we can set up sixteen kinds of brightness, changes from black to white.

4-bit processing system,

that is 32, (2 of the 5th power level grayscale), this means we can set up thirty two kinds of brightness, changes from black to white.

5-bit processing system,

that is 32, (2 of the 5th power level grayscale), this means we can set up thirty two kinds of brightness, changes from black to white.

6-bit processing system,

that is 64, (2 of the 6th power level grayscale), this means we can set up sixty four kinds of brightness, changes from black to white.

8-bit processing system,

that is 256, (2 of the 8th power level grayscale), this means we can set up two hundred fifty six kinds of brightness, changes from black to white.

10-bit processing system,

that is 1,024, (2 of the 10th power level grayscale), this means we can set up one thousand and twenty four kinds of brightness, changes from black to white.

12-bit processing system,

that is 4,096, (2 of the 12th power level grayscale), this means we can set up four thousand and ninety six kinds of brightness, changes from black to white.

14-bit processing system,

that is 16,384, (2 of the 14th power level grayscale), means we can set up sixteen thousand three hundred and eighty four kinds of brightness, changes from black to white.

16-bit processing system,

that is 65,536, (2 of the 16th power level grayscale), this means we can set up sixty five thousand five hundred and thirty six kinds of brightness, changes from black to white.

So, how many bits do we actually need?

We suggest that for a regular LED digital screen display 8 – 10 bits are enough.

For a virtual LED video wall display we recommend 10-12bits or higher.

A normal monitor can go up to 8-bit. An LED screen can go up to 14 to 16 bits

high scans and refresh rate

PWM Technology

PWM enhancement + grayscale boost

High Scans And Refresh Rate

PWM Technology

PWM enhancement + grayscale boost

one device with a value of four

REFRESH RATE

The refresh rate of an LED display refers to the number of times per second that an image is drawn on an LED display.

High performance LED displays requires a 3000 refresh rate or above as it leads to more stable broadcasting and less flickering – this is an absolute requirement for a LED screen display in a VP or XR studio. A low refresh rate will result in more scanning lines and flickering.

Scanning lines are , however, different to Moiré should be confused:

The video below by Liantronics explains this in further detail.

high scans and refresh rate
13-bit Grayscale Value Solution
Formula

Brightness = one pixel’s brightness x quantity of pixels per square meter x duty. Depends on the pitch.

So in this scenario:

P4 / 1/16duty / Cabinet size: 1𝑚2/ LED R: 280mcd, G: 440mcd, B: 450mcd

Step 1

White balance ratio: R:G:B = 3:6:1 therefore R: 220 mcd, G: 440 mcd, B: 73.3 mcd 1 LED brightness = 733.3 mcd

Step 2

Quantity of pixels in Cabinet size = 10002𝑚𝑚42𝑚𝑚= 62,500 pixels

Step3

Brightness = 1𝐿𝐸𝐷𝑏𝑟𝑖𝑔ℎ𝑡𝑛𝑒𝑠𝑠∗𝐿𝐸𝐷𝑞𝑢𝑎𝑛𝑡𝑖𝑡𝑦𝑑𝑢𝑡𝑦 733.3𝑚𝑐𝑑∗62,50016= 2,864,453𝑚𝑐𝑑

Frame rate
Frequency of the frame captured by the camera each second

The static LED only controls one LED in 1/60s.

If the scan is 36, the static LED will control 36 LED in 1/60s

Example:

If using a scan of 1/32 the brightness will be lower than the 1/11 scan.

However, the Refresh rate means the highest brightness can affect the shutter speed.

If your shutter speed is higher than 1/3840, you will see black lines.

If your LED display refresh rate is 2000, your shutter speed can not be over 2000

90 FPS

high frame rate display module example

Driver: MBI5264

Resolution: 90 x 120 pixel

Scans:30

Grayscale: 16-bit

Refresh rate: 3840Hz

Frame rate:
@60 fps
@120 FPS

120 fps