A few days ago, during an evening chat with some friends, one of them told me about his latest purchase, a 30 bit monitor.
At first, I was perplexed, then I connected and understood what they meant by 30 bit.
In a short time, chatting with all of them, I realized how in reality the colours shown on our displays are something we take for granted. So this little article wants to be just that, a small source of useful information to understand what you are speaking and how it affects us every time we are in front of a screen, even on a smartphone.
The Color Gamut
We as humans like to think we can see everything in the world to the best of our eyes. If we are particularly fortunate and lacking in visual defects that oblige us to wear glasses and lenses, we are all convinced enough to see all the colours of the universe.
In reality, it is not so, the rods and the cones of our retinas are born to visualize only a part of the visual spectrum, the one that evolution has deemed most useful for our survival.
If we could see the whole visual spectrum, we would discover a world completely different from what we see every day, for example, the crows would be white birds with shades of blue and green, the pupil of the eyes of many animals would be of a colour of all impossible to describe and at night we could read without having to access the lights.
The CIE Diagram
To help us in our understanding of how limited our visual spectrum is and how this is represented, I introduce you to a diagram called horseshoes diagram or more scientifically CIE Diagram. This funny diagram represents years of extensive research on human vision and represents all the colours visible in nature.
In the upper curve, all the colours present in the rainbow appear, if you look carefully. The numbers in blue that appear nearby represent the frequency of the colour wavelength. All the colours that appear near the edges of the diagram can be made only through the use of lasers, all the rest of the colours are mixed colours that have a more “pure” colour mixing inside. In the lower part of the diagram, there is a line called “the magenta line”, the colours present on this line are the limit of what we can perceive. For example, all the violets come from mixing reds with blues and pinks from mixing between purple and red, they are not pure natural colours.
The Color Space
Now that we understand how to read or at least look at that diagram, let’s talk about the colour space.
What is the colour space? Well, over time, having yet to produce screens with the same perfection of visible colours, the need arose to have to communicate to others the capabilities of each monitor to represent colours. Thus the colour spaces were born. The most famous in the computer science field is surely NTSC, sRGB, Adobe RGB, DCI-p3.
As can be seen from the diagram, each of these is created to cover visualization needs and occupies only a small part of the CIE diagram. Are there real differences or reasons for using one colour space over another? Undoubtedly, but it all depends on the colour fidelity you are looking to achieve. So the final device or print for the images.
The last detail, not exactly secondary in the concept of color gamut, is the monitor. As mentioned above, we would like to be able to think of having a monitor production method that provides them with the perfect quality and can replicate the entire colour spectrum of the natural world. In reality, we are still far from everything, not only that. Many monitors are not even able to reach 100% of a single colour space taken as a reference.
It so happens that the gamut of our monitor, obtained from the colours able to display, is much lower than that expected from the supported colour space.
Why then on two different screens the colour of the same images is different?
Because producing a screen is very complicated, small variations in heat or composition of the raw material are enough to generate small aberrations in the gamut of the colours, which in the end are tolerated in the production phase. All this leads to significant color differences also between the same model of screens.
More bits for colour
Over the last ten years, the world of screens had become accustomed to having a fixed number of bits for colours. The 24 bits have spread and are now a standard in the industry.
However, what does 24 bit mean? It means that for every pixel of the monitor, the possibility of choosing colours is equal to 16,772,216 colours. Talking about it in more mathematical terms means that for every pixel the colour possibilities are equal to 2 ^ 8 for each colour channel, i.e. 256 x 256 x 256 = 16.777,216
So when we hear someone talking about 30 bits, we must think that he is referring to the number of bits per channel. So he means a colour depth per pixel equal to 1024 x 1024 x 1024 = 1.073.741.824.
They are a lot more colours.
How do I activate 30 bit on my computer?
Ok calm, it’s not that simple. There are prerequisites for being able to activate 30 bits. If you are on a Mac operating system and you have a machine built by “El Capitan”, then there is a massive possibility that everything is already activated. Otherwise, your machine does not support them.
On Windows the situation is more complex, you need a Radeon pro or an Nvidia Gtx card that falls under the features of the new drivers. (Nvidia officially supports 30 bits, on non-framework cards, only from 29 July 2019 with driver 431.70)
You will need to have a monitor with enough gamut to see the difference. However, you will also have to have software that supports 30 bits, and that allows you to configure it. Many even professional software is still limited even to 8 bits but use algorithmic techniques to display a higher number of colours.
How can I make sure I work in 30 bit?
The most straightforward test is to recreate this simple black/white gradient, after activating the 30 bits in all your programs. If it appears as in the first image you will be working in 30 bits of colour, if instead, it will appear as in the second you will still have to check something in your configurations.
Is that 30 bit worth it?
It’s a long and complicated question. In reality, 30 bits are not an absolute novelty. For years, some 30bit professional monitors have been proposed as a solution for graphic designers and photographers.
Already the old Silicon Graphics systems used 12bit per colour channel, as did the NeXTSation System and some Amiga Systems.
It is useful to be prepared for what is now becoming a standard, while still maintaining backwards compatibility.