What does "calibrating a screen to sRGB" mean?

Question

I occasionally read on Internet the mention of "calibrate your display to sRGB" or "a display calibrated to sRGB".

Now, I am no expert in color management, but I have this thick book which I am reading for the fourth time now, trying to really grasp the important things. Since the subject does not for my part lean well to thorough understanding, especially with a lot of conflicting information I supplant from Internet, the aforementioned "calibration to sRGB" does not make much sense to me.

Does it refer to calibrating a display so that say, every RGB triplet maps to exactly the same real color (CIE Lab* point) as it would per sRGB? So that your monitor profile simply matches color response of sRGB? Is that what it means?

Because right now, I, for the first time in my life, used a borrowed colorimeter (Spyder3Elite) to calibrate my average desktop LCD (Dell G2410), which produced a monitor profile file, and Windows now uses it.

From what I learned from my book, Windows, assuming everything is sRGB unless otherwise specified -- meaning for instance the desktop rendering with icons and all, and what my Firefox 54 displays of untagged images -- should translate to correct real color because the system is able to correlate sRGB index-color relationships to index-color relationships of my monitor profile. I mean, that's one of the things color management systems do, no? Translate between source and target color spaces to assure correct color?

As a bonus question, what benefit is there to "calibrate to sRGB", as opposed to what I have now, if there is even such a thing as "calibrate to sRGB"?

Answer 1

I am a bit unclear of your actual question but am going to try to answer in context.

There are, a bit over-simplifying, two types of monitors out there: Wide and narrow. Narrow (or just normal) are close to but never quite sRGB.

When you calibrate a wide gamut monitor, you can make choices whether to calibrate it to a subset space, e.g. you can calibrate it to be sRGB (or several others). You can also calibrate it to "native" meaning as wide as it can display.

So the term "Calibrate to sRGB" really has meaning only for a wide gamut monitor, but more generally could apply to either native on narrow (as most are close to sRGB) or to that target on wide.

When you run "calibration" software, there are usually two events, a calibration of the monitor, and a profiling of the monitor. Usually they happen together, but they serve two purposes. Calibration is where something in your system receives a transformation matrix, usually called a LUT, which says "when this RGB value is requested display that one". It may include simply lookup values, or more complex transformations (you may see terms like 2D and 3D for example). On many computers this transformation is loaded into the driver for the video card, on some monitors it is loaded into the monitor itself (so called "hardware LUT's").

This calibration provides corrections so that your monitor is more accurate. For example, if you had a line of monitors and all calibrated to the same target, they would be more similar to each other for a given image displayed. The calibration, however, has several somewhat subjective decisions you make in addition to the (if wide) the target space, such as the color temperature, contrast, black point. These tend to be driven in part by environment (color temperature) and hardware (contrast is limited by that). So it is not necessarily true that two monitors that are "calibrated" are calibrated the same, even if to the same target space.

Now... during "calibration" there is also usually a profile phase which will measure the monitor's actual response and provide a profile to describe the monitor's actual display capabilities. This profile speaks to the color space, or more precisely to how close that monitor got to the color space. Of paramount importance if you calibrate to a wide color space, it tells color management applications which one.

So essentially the calibration gets the monitor as near a target as possible, and the profile is information to describe how the monitor was calibrated, and how well it responds.

In the days where everything was approximately sRGB, then a "calibrated" monitor was simply one corrected to be more accurate, and color management was (relatively speaking) less important since most things were sRGB and most software was not color managed.

With more wide gamut images used in editing, and/or more wide gamut monitors, now we need to translate. If you try to display an sRGB image, an AdobeRGB image, and a ProPhoto RGB image by simply sending the RGB values to the monitor, you get three very different images (regardless of the monitor's calibration, though which color space would imply which one was best). A specific color's numeric value in each color space is different.

The "calibration" produces a profile that allows color managed software to map one into the other, so a monitor calibrated near to AdobeRGB, can display an image in ProPhoto RGB by using the profile to translate the RGB values from one space to the next. Thus a color managed application displaying the same three images should display the same for all three, regardless of monitor type (so long as it is calibrated).

Note that this does NOT Mean it will look the same on a wide monitor as a narrow; there are colors one can display the other cannot. But it will be as close as practical, and more importantly consistent between images even in different color spaces for those colors actually in those spaces.

You mention the controls on the monitor - when you calibrate the monitor, it is useful to change those in certain ways (the calibration software will usually help), but that is not the driving force behind the calibration, it is the LUT table loaded. The driver will adjust both color managed, and non-color-managed applications based on the calibration, regardless of the adjustments. However, adjusting the monitor after calibration will (on most systems) break the calibration -- you will have essentially given the calibrated setup a different monitor.

Bottom line: Calibration makes the monitors more accurate to their targeted parameters; the profile allows color managed applications (and only those) to translate between color spaces (including the color space of the monitor). It takes both to be complete. But calibration to sRGB (or on a narrow monitor) means sRGB images in NON-color managed applications appear more normal. And there are more sRGB images on the web than anything else, hence I believe the genesis of your advice.

Answer 2

I was initially going to say that's it, you're done, by profiling your monitor you're all set. But then something rang a bell from my own struggles with this topic.

I've used the displayCAL / argyll software and the argyll colour management site is worth a read. It has a section on calibration vs characterisation, which, I think, basically says calibration is when you adjust your monitors controls to a base level (often a setting for sRGB - or as close as possible) and characterisation or profiling is the process of working out how far that setting deviates from the target profile and then creating a profile which allows colour management software to make the adjustments required to display colours correctly.

If I understand correctly, as long as you don't alter the controls on your monitor the profile you created should be doing it's job.

Just to add, I'm no expert just a photography / computer enthusiast so I'm prepared to be corrected / educated on this subject which seems to generate a lot of questions but few answers.