13 Replies Latest reply on Oct 14, 2008 12:23 PM by bsteinagel

    What is Monitor Gain and How Does it Affect Color Gamut?

    bsteinagel Level 1
      As I understand it, when I adjust the individual RGB controls of my monitor during calibration, I'm adjusting the gain of the monitor. Maybe I'm misunderstanding how gain works, but if a gain of 100 on all three channels gives me the brightest, most saturated colors and a gain of 0 gives me muted desaturated colors, aren't I basically reducing the number of colors my monitor can display by calibrating it? This would seem counter-productive to me.

      The reason I ask is because I have a computer monitor whose default settings are extremely bright and I can't adjust my screen's brightness to the standard of 120 cd/m2 without first reducing each of the RGB controls to 70, then fine tuning the RGB output during calibration using my Gretag Macbeth i1 Display 2 device, then reducing my monitor's brightness to achieve the appropriate 120 cd/m2.

      I've tried to search the 'net for an explanation of just what gain is but haven't been successful. Any insight is greatly appreciated.
        • 1. Re: What is Monitor Gain and How Does it Affect Color Gamut?
          Level 1
          Think of "gain" on your monitor as being analogous to "volume" on a sound system.

          On a sound system you can adjust your volume from 0 to 10. But that doesn't mean that the optimal way to listen to music is with the volume at 10. In fact, the music will probably sound terrible and distorted with the volume all the way up.

          Same with a monitor.
          • 2. Re: What is Monitor Gain and How Does it Affect Color Gamut?
            bsteinagel Level 1
            Hi Rick,

            Thanks for the quick response. So it sounds like decreasing my RGB values to 70 before calibration didn't really 'hurt' anything as far as the color gamut of my monitor is concerned? I found this was the only way for me to get the brightness down to a reasonable level. With RGB at 100 my screen was at about 240 cd/m2 even with brightness set to 0 in the monitor's OSD.

            I should also add my system specs: Currently I'm using a homebuilt Windows system running Windows Vista x64 on an Intel Quad-Core 2.88 GHz processor with 4 GB of RAM. My monitor is a 24" Dell 2408WFP LCD display. I have an nVidia 8600GT 512MB Video Card as well.

            Brad
            • 3. Re: What is Monitor Gain and How Does it Affect Color Gamut?
              (Aandi_Inston) Level 1
              But, yes, ANY form of calibration or colour management reduces the
              total number of distinct colours that can be displayed, at least if
              you are starting with an 8-bit/channel original. That's the price you
              pay.

              To see the effect, it's easiest to think of a greyscale image.

              Consider: if you have an 8-bit greyscale image on an 8-bit/channel
              monitor, and you use the image to control the colours directly then
              you get (in theory, and barring other effects) the maximum number of
              possible colours: 256. If you have any kind of adjustment to the
              colours then either
              (a) some two colours (greys) in the original map to the same colour on
              the monitor, meaning that there will be some unused shades of grey; or
              (b) the adjustment is so minor it has no effect at all.

              But, the shades of grey you see would then be a property of your
              monitor, and nothing else. That may be fine, but if you want to see
              the same as other people on other monitors, you need to do some
              adjustment. And this means a loss of colours for, perhaps, all but one
              monitor and maybe not even that.

              The same applies to all kinds of editing of images, such as
              brightening or darkening an image. It reduces the number of colours.
              To avoid this effect _while editing_ it's useful to work with a
              16-bit/channel image.

              Aandi Inston
              • 4. Re: What is Monitor Gain and How Does it Affect Color Gamut?
                (Marco_Ugolini) Level 1
                Aandi Inston wrote:

                >But, yes, ANY form of calibration or colour management reduces the
                total number of distinct colours that can be displayed, at least if
                you are starting with an 8-bit/channel original. That's the price you
                pay.

                Right, but only if the calibration is applied to an 8-bit graphic card internal to the CPU. If, instead, the monitor display has its own 10-bit LUT (or higher, like several units have these days), then the CPU's graphic card is left linear, and no decrease occurs in the maximum possible number of unique colors that can be eventually displayed on the monitor.
                • 5. Re: What is Monitor Gain and How Does it Affect Color Gamut?
                  (Aandi_Inston) Level 1
                  Good point. My discussion only covers 8-bit/channel hardware.

                  Aandi Inston
                  • 6. Re: What is Monitor Gain and How Does it Affect Color Gamut?
                    Gernot Hoffmann Level 3
                    A reduction of the luminance of a TFT monitor from
                    e.g. 200 cd/m2 to 100 cd/m2 is hopefully never done
                    by the graphics card LUTs.
                    It's IMO done by monitor electronics, using monitor
                    control menues.
                    Nobody knows what's happening internally.
                    In my experience with EIZO CG19 this doesn't lead
                    to posterization because of reduced max. luminance.

                    The graphics card LUT or the higher resolution LUT in
                    the monitor (EIZO) has to apply only small corrections,
                    if the monitor is manually pre-adjusted near to the
                    target values.
                    This doesn't reduce the number of available levels
                    considerably.

                    Reducing the luminance (in limits) doesn't change the
                    chromaticity coordinates of the primaries very much,
                    if the monitor is technically OK.
                    The gamut is not reduced. It is assumed that the
                    observer is adapted to monitor white.
                    A secondary effect is named after a scientist, whose
                    name I forgot: darker samples APPEAR less vivid,
                    though the chromaticity coordinates are the same as
                    for brighter samples.

                    Finally I would like to prove some of my statements
                    by test results for Eizo CG19, p.36 here:
                    http://www.fho-emden.de/~hoffmann/colcalc03022006.pdf

                    The luminance is only 80 cd/m2, but the chromaticity
                    coordinates are near to those of sRGB (both sets are
                    different, but the actual set is not contracted towards
                    white).

                    Best regards --Gernot Hoffmann
                    • 7. Re: What is Monitor Gain and How Does it Affect Color Gamut?
                      Level 1
                      Gernot_Hoffmann@adobeforums.com wrote:

                      > A reduction of the luminance of a TFT monitor from e.g. 200
                      > cd/m2 to 100 cd/m2 is hopefully never done by the graphics card
                      > LUTs. It's IMO done by monitor electronics, using monitor
                      > control menues.

                      Someone once told in this forum (Andrew Rodney as far as I recall)
                      that if one changes the "gain" of an ordinary TFT monitor (not the
                      LED ones though) by adjusting the individual RGB controls using
                      monitor control menues, the adjustment really happens in the graphic
                      card LUT. Isn't that true?

                      --
                      Regards
                      Madsen
                      • 8. Re: What is Monitor Gain and How Does it Affect Color Gamut?
                        Gernot Hoffmann Level 3
                        Thomas,

                        the free GMB program Calibration Tester shows the
                        contents of the graphics card LUTs.
                        Altogether three programs, mentioned here on p.20:
                        http://www.fho-emden.de/~hoffmann/measgamma10022004.pdf

                        If the luminance settings of the monitor are above
                        the target value e.g.100 cd/m2 for a calibration
                        by instruments, then the graphics card LUTs are
                        trying to reduce the luminance (old example in the
                        doc, also p.20), for instance from 110 to 100 cd/m2.
                        Such a case would reduce the resolution a little.

                        As tested by Eizo CG19:
                        The adjustment of the monitor by monitor menues
                        doesn't affect the graphics card LUTs. In fact,
                        the calibration by GMB ProfileMaker5 guides the
                        user to adjust the monitor dynamically/interactively
                        so, that the LUTs contain finally almost no correction.
                        In this sense the old example above wasn't perfect.

                        This is the classical method, which I'm applying as
                        well to Eizo CG19, though this monitor offers a
                        calibration by ColorNavigator, based on monitor-
                        internal LUTs with 10 or 12 bits per channel
                        (leaving the graphics card LUTs at identity y=x).
                        For certain reasons I'm not using this feature.
                        One reason: then it would be impossible to have a
                        look at the contents of the LUTs.

                        Theoretically the result should be better for high
                        resolution LUTs, but I wasn't able to detect banding
                        or posterization after applying the classical method.

                        Best regards --Gernot Hoffmann
                        • 9. Re: What is Monitor Gain and How Does it Affect Color Gamut?
                          (Marco_Ugolini) Level 1
                          Thomas G. Madsen wrote:
                          >Someone once told in this forum (Andrew Rodney as far as I recall)that if one changes the "gain" of an ordinary TFT monitor (not the LED ones though) by adjusting the individual RGB controls using monitor control menues, the adjustment really happens in the graphic card LUT. Isn't that true?

                          No. It is *possible* to control the monitor's settings, but only if it is connected to the CPU by a communication cable (usually DDC/CI-VESA compliant). I've certainly never heard that it's possible to affect the CPU's display card from the display (and I cannot think of a reason why that would even be desirable).

                          Apple's monitors allow for control of brightness from the CPU (the intensity of the backlight), but nothing else (not contrast, not the RGB signals).
                          • 10. Re: What is Monitor Gain and How Does it Affect Color Gamut?
                            bsteinagel Level 1
                            There certainly is a wealth of information on this forum, and I'm glad to have found it. Thanks everyone for all the knowledge. I'm always glad to learn more. Thanks for all your help and please keep the posts coming.

                            Brad
                            • 12. Re: What is Monitor Gain and How Does it Affect Color Gamut?
                              Level 1
                              Thomas G. Madsen wrote:

                              > Thanks, Gernot

                              And Marco :)

                              --
                              Regards
                              Madsen
                              • 13. Re: What is Monitor Gain and How Does it Affect Color Gamut?
                                bsteinagel Level 1
                                So then, by reducing my RGB controls to 70 before calibraton I am effectively reducing the number of colors it can display? If so, at what point does this become an issue? Is there a way to use Photoshop's soft proofing feature along with my current monitor's icc profile to determine if I'm missing out on a large part of my monitor's gamut?

                                Brad