Because it is essential, quite simply! And why is it so? Because it is the starting point of the work you perform on your pictures, because you want to get the best out of them and your eyes are unable to accurately support you in this process.You should be convinced by now!
Key points if you are a beginner ...
Here are the key points to remember on monitor or display calibration. The rest of this page will be dedicated to those who want to go into more details.
The monitor is our main working tool at home. And this main working tool is not always accurate when displaying colors, unless you spend more than $2,000 in it, and things consequently improve.
Moreover, monitors have three main drawbacks for us who edit images: when they leave the factory, they're always too bright, too contrasted and the image is too cold. I could also add that their image depends a lot on the angle at which you're watching them (because of their technology).
But nowadays, as it wans't always the case, powerful and affordable tools exist (less than $250) to solve those issues. We are thus going to calibrate our monitor using a tool much more efficient than our dear human eye: a calibration sensor, also called colorimeter.
Obviously, this can only be done with a colorimeter, because to give you a simple example, how do you want to adjuste precisely a monitor luminosity at 100 Cd/M² to the naked eye... Certain people are granted the absolute pitch, but I don't know anyone with an absolute vision!
At least do your self a favor: perform a display calibration with a monitor sensor, a colorimeter. You have no idea how it will change your way of working! Considering their current cost, you don't have any excuse not to purchase one anymore!
Just ESSENTIAL for someone working with images on a computer, screen calibration cannot be done efficiently without a colorimeter (sold with ICC profile creation software). Prices have really dropped down since Spyder4Express or Colormunki Smile colorimeter can be found at a price around $100 nowadays (versions I don't recommend though) and "Pro" versions are just a bit more expensive, around $170. This is excellent value for money. The references today are i1Display Pro from X-Rite or Spyder5Elite from Datacolor, and cost $250 incl. taxes. It doens't seem too expensive to me compared to the price of digital shooting equipment, and to the money spent on ink cartridges and paper, or even more the price of a powerful computer, regarding its interest.
Monitor calibration is performed in two steps :
calibration or gauging in itself;
It is only during that second step that the monitor's ICC profile is created (device characteristics). At first, I am going to clarify those two terms. Even if I am going to put an emphasis on calibrating with a colorimeter, I will also explain in a second time why it is not only essential, but also very different from calibrating to the naked eye or using a print. Then in the next page, I will answer the question "how to?" and in a third part, I will benchmark almost all calibration sensors on the market. Then, I will end up with a summary where you will find all my purchasing advice for calibration sensors depending on each device category: laptop, iMac, iPad, office monitor, graphic arts monitor.
Calibrating a monitor consists in performing three REALLY IMPORTANT adjustments... and making one important choice!
On the one hand, neutralize color predominances hence display defects of the screen,
On the other hand, adjust your monitor's settings to enable to display the right luminosity and contrast level,
Ensure that the monitor displays the widest possible range of colors,
And finally, make the right choices of monitor technology!
Under no circumstances can those adjustments be performed to the naked eye, because even if the human eye is very good for comparison, it is also theoretically quite bad in terms of visual acuity.
1 - Correct color predominances and optimize color range
As seen in the pages dedicated to generalities about color management, all color reproduction devices reproduce them with alterations that are proper to each and any of them. We would like our monitor to display a neutral grey, but it displays a grey with an unexpected color predominance, without even taking the printer's defects into account, etc. Calibration will thus consist into sending to the monitor a serial of RGB signals which absolute color we perfectly know ( XYZ values in CIE XYZ color space or La*b*) and to measure with a colorimeter - also called colorimeter - how they are really displayed.
For instance: if I try to display a 128, 128, 128 RGB signal on a non calibrated monitor, there is very little chance I will see a perfectly neutral grey appear (even if things are better since 2012). Most probably, it will display a grey with a slight color predominance (reddish, greenish, etc.). The sensor will measure the "real" color displayed (hence its L*a*b* value) and place the information in a special file: the ICC profile of this monitor. With the created profile, Photoshop, for instance, will now know how to modify a RGB signal in order to display the right L*a*b* color, in this case, a neutral grey. It means that when willing to display a neutral grey, 128, 128, 128, the graphic card will have to send a signal like 124, 128, 128 in order to take into account the monitor characteristics, here a defect in the reds. By doing this, the monitor will display the largest color range possible. On top of that, you'll see how your sensor can help you with additional adjustments in the next step.
The "bad" surpise of wide gamut monitors
A new monitor generation appeared: wide gamut monitors. Those monitors are able to reproduce at least 98% of the Adobe RGB 98 color space and can even reach 110%. However we have our habits with our monitors displaying sRGB only.
Almost all icon colors will appear very saturated in the task bar or in the Dock before and after calibration. Mac OS and Windows can't manage colors. You will only enjoy the benefits of your monitor calibration in programs featuring color management, like Photoshop or the Viewer. Your images will be beautiful in Photoshop and highly saturated/contrasted in the Windows or Mac explorer...
As for the web, it will depend a lot on the browser you're using. A real mess, still in 2014, but I go into further details about it in my page dedicated to color management on the web (July 2016).
2 - Adjust monitor brightness
A point also often neglected is screen brightness adjustment, so that the brightness of the picture displayed on screen is close to the printed one. This adjustment can not be achieved with to the naked eye, just like color predominance correction, and requests a calibration device which is going to measure precisely the real monitor brightness level depending on the instructions you'll be giving to your program. It is the gauging phase.
Caution! The monitor gamma by default is also an important parameter. If you decide to buy a graphic art monitor, it is likely to have a 1.8 gamma. Calibrating it at 2.2 isn't very useful, and it could even be worse! Your monitor can have a good brightness level but a 1.8 gamma and you will still get too dark prints. Not so easy to deal with that! We will come back to that point later on.
3 - Adjust monitor contrast
Another point that is also often neglected the monitor contrast adjustment. Contrast adjustment is used to set the black point level for your monitor. This can clearly be an issue for laptop monitors calibration that never feature this setting. The colorimeter will have to perform it automatically.
4 - Are all monitors equal?
I invite you to read this page where I give you purchasing advice, my opinion on choice criteria (especially for screen technology for photographers) as well as my point of view on things...
Recommendations to choose your monitor for photo edition
Let's now have a look at the two steps of calibration process for a monitor: calibration and characterization, or the report of its precise colorimetric characteristics.
Calibration & Characterization
As I already said several times before, the calibration process is in fact a two steps process: a gauging followed by a characterization (except for isolated cases like the iPad).
Monitor calibration or gauging
In order to make sure that this color reproduction device that is a monitor is working in optimum conditions, we'll have to calibrate it, or rather gauge it, meaning that its basic functioning must be optimized and it must be placed in known and preferably stable conditions. For a monitor, one of the color workflow tool we are talking about in this page, the calibration process is used to set once for all:
Maximum monitor brightness or white point;
Color temperature - in Kelvins -;
And possibly minimum monitor luminosity or black point.
This operation also called gauging can be done in two different ways depending on the quality of the monitor purchased, but always using a sensor:
With a non graphic art monitor, this is to say almost all monitors, this is done through the monitor menu and the colorimeter which, during this stage, operates as a gauging tool. A collection of colored icons appears on the monitor to enable calibration. One of the most important points is to know if the software offers the possibility to control the maximum and minimum quantity of light that it has to display precisely. This one should ideally be close to 80/140 candelas per m², depending on the luminosity of your working environment, so that the luminosity of your print will be very close to the luminosity of your picture on the monitor. This can only be done with the help of a measuring device. A human eye is absolutely unable to achieve such a process without elements of comparison.
With a graphic art monitor, you simply need to fix those four targeted values in the software menu and launch the calibration process that will be done automatically (characterization is automatically performed afterwards). Note that once the monitor is characterized - in other words profiled - you should never modifiy those settings! Otherwise, you will have to perform the characterization again, and thus to create another ICC profile for those new calibration or gauging conditions.
As I told you in the first page of this file - introduction to color management - light wave lengths fixed by CIE for three primary colors are 700, 546 and 436 nm. To produce these colors precisely, a monitor lights up pixels of less than 0.30 mm (non retina screens hence around 90 dpi) in front of which RGB filters have been placed. The quality of the filters will determine the quality of the monitor. However, as it is a built-in technology, these filters cannot be changed. You can light them more or less, but you cannot change them! So if the monitor has a blue filter emitting at 438nm instead of 436nm, it is absolutely irretrievable. There is no way to transform this color and it goes the same way for the two other primary colors. But then, what is the colorimeter measuring and what is an ICC profile for, if the three primary colors are not ideal and cannot be changed?
Well the answer is quite simple! The colorimeter measures precisely what the color is - light wave length - of the RGB filters of a monitor at first ( possibly at different luminosity levels depending on the type of ICC profile creation software). Now, we know that colors multiply to infinity (between 2 and 8 millions depending on your visual acuity), therefore the three primary colors are only three colors among millions - a bit more if you consider the different levels of luminosity possible for each of these three colors - the monitor will have to display. But all other colors are always a percentage of three or two primary colors. So it will be easy to slightly change the percentage of those primary colors to, finally, correctly display any color. Only the three primary colors will never be correctly displayed by this monitor, if it has a defect. It is pretty funny and almost crazy: display colors correctly with three corrupted basic colors !!! And yet...
It is during this second step that the ICC profile of the monitor is really created, in accordance with the settings optimized during the previous step, meaning during calibration. We are now going to measure the color characteristics of the monitor placed in "ideal" working conditions or at least known and precise conditions (ideal meaning that the monitor wouldn't need to be profiled anymore). Then, the calibration software send a series of RGB signals to the monitor and the real colors displayed are analyzed and compared to the ideal colors - L*a*b* - of the ICC consortium using a monitor sensor - also called colorimeter. Caution! If you perform the characterization with your eye, you will only perform a comparison and not a measurement. So, this step is impossible to perform with free gauging tools based on color patches comparison. In the end, the software will create a color identity card of the device by measuring :
The color space it is able to reproduce compared to the L*a*b* color space (also called gamut); it is the result of white point, black point and maximum saturation of the filters placed in front of each pixel of your monitor;
And how it is displayed - what RGB signal for which L*a*b* color.
Very important: all color alterations displayed on screen compared to L*a*b* colors will be carefully saved in a special file, the ICC profile of this monitor. When the graphic card will want to display a certain L*a*b* color, it will know exactly what "amended" RGB signal has to be sent for the color to be displayed properly, taking into account those characteristics. An ICC profile can thus be quite a large file because it contains an impressive number of information. The number of colors possibly displayed on a monitor is indeed incredibly high - a very good eye can distinguish, let me remind you, almost 8 million colors! Using your eye for such a process can only lead you to an approximate result even if sometimes this can do the trick as a monitor gamut is not very wide - even if new technologies using LED for instance increased it. Even if it is still often close to sRGB, more and more monitors are now able to display Adobe RGB 98, noticeably wider, what explains why calibration devices are changing these days, by the way. Many photographers had a lot of problems with the first generation of LED monitors, a technology that is now under control (summer 2012).
To be remembered!
Monitor calibration with a good calibration sensor is mandatory and totally affordable nowadays.
Never buy first price colorimeter (Spyder4Express ou Colormunki Smile) not recommendable and not so much cheaper than Pro or Elite version, that are perfectly working.
Pro or Elite version can be misleading: there are no pro or amateur sensors; there are colorimeters that work very well with any monitor and colorimeters that are so basic that they will often deliver a calibration of poor or unstable quality. It is thus hard to recommend them. "Even" amators shoul buy "Pro" sensors!
Calibrate your monitor between 80 and 100 Cd/m² if you intend to have your work printed and calibrate at 120/140 Cd/m² if you are essentially editing your images for the web.
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