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How Infinity Solution Increases Grayscale Levels
How Infinity Solution Increases LED Display Grayscale Levels
After expanding the dynamic range through hybrid driving technology, it is necessary to further subdivide the brightness range between the brightest and darkest levels into more intermediate grayscale levels, enabling the display to reproduce richer image details and improve overall tonal smoothness.
With conventional PWM driving technology, there are mainly two approaches to improving grayscale levels:
1. Increasing the GCLK frequency
Increasing the GCLK frequency is one of the conventional methods for achieving higher grayscale levels. For an 8-scan designed product, a 16-bit grayscale level requires a 32 MHz GCLK frequency, while an 18-bit grayscale level requires a 120 MHz GCLK frequency. This places significant challenges on the manufacturing process and cost of driver ICs. Furthermore, as LED pixel pitches continue to decreases and scan rates increase, these challenges become increasingly significant, making GCLK frequency a bottleneck for further improvements in grayscale levels.
2. Dithering
Dithering is a technique that improves perceived grayscale levels by introducing controlled noise or patterns. By intentionally adding high-frequency noise or distributing quantization errors during the quantization process, dithering converts concentrated quantization errors near color banding boundaries into finer and more dispersed patterns. This leverages the spatial integration characteristics of human vision to achieve smoother visual transitions. In other words, dithering enables display systems with limited color depth to simulate more colors or grayscale levels.
The brightness perceived by the human eye is the result of luminance integration over a certain spatial area and time period. Through spatial and temporal dithering pattern modulation, local pixel blocks or consecutive frames can be driven with different illumination counts. By alternately displaying adjacent grayscale levels through controlled flicker patterns, dithering enables finer grayscale levels and improves tonal smoothness. A specific example is shown in the figure below.
For example, in the case of the spatial modulation mentioned above, to display a 0.5 grayscale level, it is only necessary to make half of the pixels within a certain pixel area display 1 grayscale level and the other half display 0 grayscale level. Due to the spatial perception characteristics of human vision, the grayscale level perceived by the human eye is approximately 0.5 grayscale level. Similarly, if half of the video frames within a certain period display 1 grayscale level and the other half display 0 grayscale level, the temporal perception characteristics of human vision enable the perceived grayscale level to also be approximately 0.5 grayscale level.
In general, dithering technology can improve grayscale levels and enhance tonal smoothness. However, it also introduces issues such as flickering and instability at low grayscale levels. To some extent, these artifacts can affect visual comfort during viewing.
Are there any other methods to further improve grayscale levels and tonal smoothness? In general, the brightness of an LED display is controlled by the current amplitude and the corresponding illumination duration, expressed as:
Where PAM represents the drive current amplitude signal used to illuminate the LEDs, PWM represents the illumination duration at the PAM-defined current amplitude, and Luma represents the brightness output achieved through the combined control of both parameters.
With the hybrid driving technology in the Infinity solution, pixel-level PAM modulation further enhances the grayscale levels based on the conventional pure PWM modulation approach, enabling higher grayscale bit depth.
In terms of brightness generation, assuming that the LED brightness has a linear relationship with the driving current, the average brightness under hybrid driving can be expressed as:
If the PAM amplitude is fixed,then
In this approach, the 
is quantized into M levels, with a PWM control period of T and an LED turn-on duration of 
.
For grayscale representation based on PWM+PAM hybrid driving, assuming a PWM resolution of 
and M discrete PAM current levels, the theoretical total number of grayscale levels can be expressed as:
Compared with conventional pure PWM driving technology, hybrid driving greatly expands grayscale capability, enabling smoother rendering at low gray levels while effectively eliminating flicker . With NovaStar Infinity Ultra High Image Quality solution, PAM achieves up to 8 bit depth and PWM achieves up to 16 bit depth, enabling a theoretical maximum grayscale levels of 24 bits through combined modulation.
