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LCD Monitors And The Maximum Number Of Displayed Colours

LCD Monitors And The Maximum Number Of Displayed Colours - Look carefully at the maximum number of colours an LCD monitor can display when purchasing a new one.

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General Photography

Even though the maximum number of colours a model can display is often shown, few people pay attention to this figure as most products today can often display more than 16 million colours and it's unlikely the user will be  dissatisfied because the product displays too few colours. However, there are a few pitfalls associated with this that people should be aware of.

The LCD monitors currently available for PC use need to accurately display full-colour video signals in the number of colours generated when using eight bits for each RGB colour (for a total of 24 bits) input from the PC. Using eight bits for each RGB colour, we can generate roughly 16.77 million colours, based on the following calculations:

  • 8-bit (28) = 256 tones
  • 256 tones (R) X 256 tones (G) X 256 tones (B) = 16,777,216 colours
  • 16,777,216 colours ≈ 16.77 million colours

In regards to this figure, two points need to be kept in-mind: firstly, not all leading LCD monitors can reproduce the entire full colour range of approximately 16.77 million colours and secondly, this full range of 16.77 million colours can be achieved in different ways.

The LCD monitors currently available generally fall into the following three categories with respect to the maximum number of colours and method of colour reproduction:

  Maximum Display Colours  LCD Panel Specs Tone Reproduction Approximate Price
1 16.77 million  8-bit Excellent High
2 16.77 million  6-bit + FRC Good Medium
3 16.19 million / 16.2 million  6-bit + FRC Fair Low

Only the Type 1 LCDs in the table above achieve full colour in the true sense of the term, reproducing each RGB colour at eight bits on an LCD panel operating at eight bits. Products that fall into Types 2 or 3 offer virtual full colour. Virtual full colour products cost less to implement, but generally offer inferior capacity to express gradation than true eight-bit LCD panels.

As both type 1 and 2 displays show approximately 16.77 million colours it can be hard to identify the applicable type from a catalog. An LCD panel operating at eight bits is superior in some ways with respect to picture quality, and users are advised to be careful when choosing monitors for graphics applications. (Note that in some cases, the figure of 24 bits, 8 for each RGB colour, is used instead.)

FRC stands for frame rate control and put simply, it's a system used for increasing the number of apparent colours by manipulating the frame rate. For example, by switching rapidly between white and red, a colour which the human eye perceives as pink will be created.

An LCD panel with six-bit operation plus FRC can actually generate just 262,144 colours (six bits [26 = 64] to the third power (for each RGB colour). FRC can be applied to each RGB colour and we can change the display interval between each of the LCD panel's original colours (in the case of four-bit FRC) to generate three simulated colours between each pair of individual colours. For each RGB colour, this adds the following number of simulated colours: (6 bits – 1) X 3 = 189 colours. The total number of colours is obtained by calculating (6 bits + 189 = 253) to the third power (each RGB colour) which equals 16,194,277 colours (approximately 16.19 or 16.20 million colours).

Some products take this further by making it possible to reproduce approximately 16.77 million colours by operating the number of bits exceeding those with traditional FRC to generate even more stimulated colours, then taking from these the eight-bit (256-gradation) scale needed to achieve full colour on an LCD monitor.

The difference in picture quality between eight bits and six bits plus FRC is often not apparent on visual inspection but by minimising environmental lighting (for example, by dimming lights) you can make such differences easier to spot. Displaying gradation patterns that change linearly, one going from shadow to highlight, can also highlight such differences.




Above images: sample gradation display using a full-colour display operating at eight bits (left) and virtual full-colour display operating at six bits plus FRC (right). While this display exaggerates the difference to make it easier to see, eight-bit operation generally offers greater gradation display capability.

It's also worth noting that under real-life conditions, factors other than the panel can also significantly affect picture quality.

Visit the EIZO UK website to see the full line up of EIZO monitors. 


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