Color Managed Monitor I

Let’s get rolling: after we described the principles of CM (Color Management) and how they can be help us making our photographic experience less of a pain, let’s move on with the first practical step: the monitor.

Preamble (man, that sounds serious)

Now before moving further (well, before starting, really…), I just would like to make a couple of points:

• There is no point color managing a monitor if you leave your printer “uncolormanaged”. That is why there is so much importance on CMS (for system). The CMS should include (or at least take into account) all the components of your graphic chain: camera, scanner, raw processing software, editing software, monitor, printer… See now why I started a blog on Linux Photography?
• We will not deal with scanning in detail. We also assume that the image we got from the camera is in AdobeRGB (or sRGB), so there is nothing special to do on that side. The fun begins when you upload your pictures from the memory card onto your (Linux) computer.

Monitor – generalities (man, that sounds boring)

In the old times, we had CRT monitors: huge, heavy and bulky, but with excellent color rendition. The first generations of flat screens were really not up to par with their ancestors when it comes to color accuracy (remember, we still talk about photography here, not gaming…). It was that bad that they were considered impossible to use for photographic work. Things have evolved since and apparently, the current technology is fine for a photographic usage – I still have an old CRT

The French magazine Chasseur d’Image started testing (flat) monitors and, while some models do better than others, most of them (even cheap ones) are decent enough. However, a cheap laptop screen is out of the game…

Another warning: screens are sold to look nice and deliver a flattering image. When you go through the process of calibration (putting your screen in a color management ready state) the image will look a lot less flattering. Usually yellow and unappealing.

• First, remember that even if less flashy, that is closer to “true colors” which is what we are after (if not, then you should have stopped reading long ago).
• Second, you will get used to it: when the screen changes from its nice, contrasty, blueish colors to a yellowish unappealing image, it hurts the eyes. Now look elsewhere for 2 minutes and go back to it: without direct comparison, your eyes adapt.

Monitor calibration: getting an ICC profile

We said earlier that what we need is an ICC profile (or ICM for Monitor, but it is essentially the same thing) that describes how the monitor displays colors. The idea is to “ask the monitor to show a pure red and measure what we get”. Do the sames for different colors and intensities and you get a table that says how this specific monitors displays color. Yes, the table is the ICC profile.

Now since things can never be simple, your ICC profile will match that monitor with these settings. Change your brightness and you need to redo the operation. It is advised to redo it anyway every month (or so) to take into account the aging of the monitor…

In order to do the measurement, you need a piece of hardware – our eyes are not measuring instruments… The price starts at about $80 up to several hundreds. I have the cheap version (the first one that was affordable) a Colorvision Spyder. Unfortunately, there is currently no driver for Linux for the device, so I have to generate my profile in Windows. Some models are supported by Argyll CMS (we will talk about Argyll later), but mostly top of the range (ie, more expensive) models.

So after you stick your colorimeter on the screen, you are asked to tune your brightness and contrast parameters (remember not to touch them anymore…) and the software starts drawing color patches on screen that are measured by the hardware. All of that takes a few minutes and you end up with an ICC (or ICM) profile.

That is the simple version. If you take a more pro approach, you will need to chose your gamma, white point, and possibly further tweaks… Let’s just say that 2.2 gamma and 6500 K white point (the defaults for PC) is all right, unless you know what you are doing and why.

You can get your Profile in C:/Windows/System32/spool/drivers/color (?!??) and reboot in Linux.

Using the profile in Linux

The profile we just created contains 2 things:

• information for the video card about how it should display colors by default. That is called calibration: brining the monitor to a known default state of displaying colors. This part is loaded by the video card and makes a difference on how everything is displayed on your monitor (makes it yellowish).
• information for color management aware programs about how to fine tune color rendition. This part is only used by the specific software (most recent version of The Gimp, Cinepaint, Scribus and others)

We will just talk about the first step for now. Basically you need to tell your video card to display colors according to the monitor profile. There are two utilities that do that for you: xcalib and dispwin (part of Argyll).

Basically, you just enter:

xcalib /path/to/iccprofile.icc

in a terminal and you should see your screen turning yellowish (that is a good sign, remember). An equivalent would be:

dispwin /path/to/iccprofile.icc

xcalib (web) is a little utility that only loads your profile information into the video card. dispwin is part of a very broad range of (command line) utilities for CM called Argyll CMS (web). Argyll CMS allows (for the parts I understand):

• to profile a monitor with selected hardware
• to load profile information in the video card (dispwin)
• to generate a vrml file representing the gamut of one or more ICC profile or the colors used on one image (more on that later)
• to transform images from one profile to another (more on that later, too)

While neither xcalib nor ArgyllCMS are part of the readily installable software range of Ubuntu/Debian both provide binary versions for X86 on their site. They are not difficult to compile either, but need quite a lot of “dev” files (for Xorg, most notably). I have and AMD64, so I had to recompile.

Summary

When we are there, we have a screen under Linux that is calibrated. That is, the screen is ready to display “true colors”. More accurately, it is ready to display colors that are as close as possible to the “objective colors” of your camera image, defined in AdobeRGB standard. But in order to not just “be ready” but really to “go and do it”, it needs a “color aware” photographic software.

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