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What is the Monitor sRGB Mode Preset?
Having purchased a Mitsubishi 930SB 19" CRT monitor, I immediately set out to calibrate and profile it. In doing so, I encountered a very interesting option in the monitor's On Screen Menu color settings: sRGB mode. This article looks at the feature in more detail.
Monitor Profiling & Calibration
Clearly, all photographers should be calibrating and profiling their monitors if they care about the look of their prints or intend to publish on the web. Without profiling, your monitor's representation of color will be different than another person's display of the same image, and of course your prints won't match what you see on the display. Novice photographers often make the mistake of trying to adjust the colors of an image in Photoshop according to what they see when they print the photo. Not only is this a waste of time, but it will be a frustrating, never-ending process as the colors will never "look right".
A "profiled" monitor will represent colors accurately when displaying images in any color-aware application (such as Photoshop). When combined with a "profiled" printer, it is often possible to have prints match the on-screen representation quite faithfully (excluding the difference between a print's reflectivity and monitor's luminance).
Calibrating the monitor before profiling will ensure that the widest available gamut from your display is available for representing your color images. It also ensures consistency of your monitor over time, as all monitors suffer from changes in the way the phosphors generate light for a given quantity of electron excitation. This "color drift" needs to be corrected (through calibration) or else the accuracy of your profiles will degrade over time.
Typical Calibration Process
When calibrating your CRT monitor (LCDs don't offer the same degree of control), you are instructed to modify the Red, Green and Blue gain (levels) of the monitor itself, in addition to the brightness and contrast settings. The contrast is set to 100% while the brightness level is set to an optimum balance between shadows and highlights (giving the greatest dynamic range for a particular set of inputs). Setting a brightness level too low will decrease the ability to discern shadows, while a high brightness level will clip the highlights.
Changing the individual color gain values causes a shift in the White Point or color temperature of the display. With the help of an external colorimeter (such as the OptixXR), it is easy to determine these settings. Often, you'll want to target your display for a white point of 6500 Kelvin. For my monitor, this meant settings of:
|Calibrated 6500K Settings|
Monitor Color Temperature Presets
My monitor provides 4 color presets, that attempt to approximate the settings required to produce the most popular color temperatures for display (9300K, 8200K, 6500K and 5000K). These all had default settings for each of the RGB gain values to produce a close approximation of each color temperature target. For my particular monitor (the Mitsubishi 930SB), the default gains for each color temperature are:
|Monitor Default Gain Settings|
In a more general context, the gain curves for each RGB setting across various color temperatures are displayed below. There were captured from my Mitsubishi monitor, showing the non-linearity in output.
|Mitsubishi 930SB - RGB Gain Curve vs Color Temperature|
With each of the four color temperature presets, one is also able to make adjustments to the individual RGB gain values (and/orcolor temperature) if desired. In my case, I will use the 6500K preset and adjust with my own gain values as dictated by the Monaco EZcolor software.
Monitor sRGB Preset
Once the monitor has been calibrated, a profile is generated, and then the photographer will proceed to decide on a color space to work in (usually sRGB or Adobe RGB). sRGB is the most popular as it is the closest approximation to what a "typical" viewer will see in an unprofiled/calibrated display or non-color-managed application (such as Internet Explorer or Windows XP).
If you are creating images for the web or sharing them with friends, sRGB may be the best target space for your images, as the non color-aware applications on their end will default to sRGB. Even if you tag your images with an ICC profile (such as Adobe RGB), most applications don't read and interpret the profile before display and hence the definition of non color-aware.
Some CRT monitors are providing a present called "sRGB" in their color adjustment menu. I have seen this available on many CRTs, including some Mitsubishi and NEC monitors.
This fifth option appears in my On Screen Menu's color setting presets: sRGB. If you select this preset, you'll notice that the RGB gain values are no longer available for modification, in addition to the brightness and contrast settings. This mode is likely to confuse anyone who is just starting to learn to calibrate their monitor.
Does it automatically calibrate your monitor and tweak it to match the color profile of sRGB mode? No!
Unless you have a very high-end monitor with self-calibration capabilities, there is no way that the monitor can adjust its output to match an absolute reference (such as sRGB), let alone remain constant over time (i.e. stay calibrated). All it can do is adjust the gain of the individual outputs (the electron beam's strength), and then make some assumptions about what the actual individual phosphors will produce in the way of resulting intensity.
Don't use the Monitor's sRGB Preset Mode!
Over time, the CRT phosphors lose their ability to generate visible light for a given quantity of electron excitation. This is known as "monitor drift". In fact, a normal lifespan for a daily-use monitor may be as short as 2-3 years. The drift will therefore change the resulting image on the display for the same input from the electron gun (or software application).
Since the CRT can't measure the output of the phosphors directly, there is no integrated correction for this drift over time.
The Monitor's sRGB mode is an attempt to provide a calibrated (and possibly profile-matched) preset for display, but clearly, this is impossible (except on the most expensive self-calibrating monitors). While it does provide you with a starting point that might have closely approximated the color space or reasonable calibration setting, it cannot hold true over time.
Therefore, I strongly suggest that you don't use the Monitor's sRGB mode if you care about color management.
One of the benefits of this preset on the monitor is that it locks out any user adjustment to the brightness, contrast or RGB gain values. While this is nice (in that it avoids accidental changes), it also means that you will have no way of calibrating the monitor to the most appropriate levels.
You can still create a monitor profile for your CRT in this mode, but you are not starting with the optimum gain and intensity settings and therefore will have to rely on more adjustment in the video card's mapping tables (less preferable).
Given the existence of a "Custom" color mode preset and the use of an external sensor (such as the Optix XR), one should not use the monitor's sRGB mode.
Quantitative Measurement of sRGB Preset
Soon, I intend to measure the actual quantitative differences in the use of this preset over a properly calibrated and profiled setting. For now, here are the measured color temperature and intensity readings:
|Monitor sRGB Preset||6442K x=0.314 y=0.332||68.08 cd/m^2|
|Calibrated 6500K||6524K x=0.313 y=0.325||100.14 cd/m^2|