24 Replies Latest reply on Jan 29, 2009 4:58 PM by (Kyle_Creasy)

    Monitor Gamma - How does it get set?

      Hi, first post here. This is a very general question that I've never quite understood. (I'm using a Monaco Optix XR to profile a crt - setting the gamma in the software to 2.2.)

      I'm confused about how setting of gamma works. The way that it's commonly described, calibration involves the physical hardware adjustment of the monitor - brightness, contrast, and gamma. The colorimeter aids me in setting the preferred values. Then the profiling process involves the software adjustment - to fine-tune the colors.

      What confuses me is that I have never seen a monitor with a hardware gamma adjustment option. So if I'm setting a gamma value in the software, am I to believe that the software is somehow physically adjusting the monitor's gamma value to 2.2? Or is it purely a software adjustment that gets saved in my profile file - along with the color correction adjustments?

      Thanks alot!
        • 1. Re: Monitor Gamma - How does it get set?
          Lou Dina Level 3

          If you are using an LCD monitor, and assuming it is not a "high end" unit (ie, very expensive), all modifications to your monitor display are written to your video card, with one exception...the brightness of your backlight, which is an analog control.

          Even when you adjust contrast, color, etc, using your monitor controls, these adjustments get sent to the video card. They relally are not happening at the monitor at all, unless you have one of those high end monitors.

          So, when you plug target settings into your profiling software, (ie, gamma, white luminance, white temp, etc), you are prompted to adjust a number of dials as you go through the process. Depending on the software, monitor, video card, etc, you may have more or fewer options. The only real monitor control is the white luminance, which you adjust to your target setting. The rest are sent to the video card to give you the target settings you requested in the software.

          After the software displays and reads the patches, it compares your monitor output to the originals, then writes curves to your video card, one for red, one for green and one for blue. These curves adjust color, gamma, etc., to match your target settings as closely as possible.

          CRT monitors have many analog controls that allow you to set white and black luminance, color temp, contrast, etc, independent of the video card, so you can get very close to your target settings BEFORE sending curves to the video card (these curves are usually minor refinements if you have adjusted your analog controls to get you close). Same with a high end LCD. Most people today use a medium to low cost LCD, so bigger adjustments need to be written to the card in order to match your target settings.

          When the profile is complete, the software automatically installs this profile as your default profile. No need to do anything. A color managed program like Photoshop will use this monitor profile for display automatically.

          Hope that helps and is clear.

          Regards, Lou
          • 2. Re: Monitor Gamma - How does it get set?
            Level 1
            Wow, thanks Lou for the thorough response! This helps alot. The reason I ask this is because I have a Matrox P650 dual video card. It has two LUT's. If I calibrate/profile one "standard" crt (Monitor 2), then calibrate/profile the other standard crt (Monitor 1 - my main monitor), saving the profile from Monitor 1 as the official profile that starts with Windows...

            How much of my Monitor 2 calibration/profiling effort will be retained later on, when I'm viewing a non-color-aware software such as Firefox on Monitor 2? Based on your response, I'm guessing nothing would be retained except for the brightness, contrast, and color temp that I dialed in thru hardware. I just wanted to verify that Monitor 2's gamma setting would not somehow be retained - maybe due to having 2 LUT's on the video card? And now that I think of it, the monitor's color temp adjustment is probably in the video card as well and not really a monitor adjustment?

            Thanks again. This is something I wondered about for years, but could never really put into words.
            • 3. Re: Monitor Gamma - How does it get set?
              Lou Dina Level 3

              I'm not sure I have the answers to all your questions.

              First, Firefox has a free Add-on (Tools > Addons > Get Addons, then search for Color Management) you can install that activates color management when browsing with Firefox. You need to specify the profile you will use for color management, so you may only have color management on one monitor.

              My video card is a Matrox Parhelia card, and has three monitor ports, but only 1 LUT, and only one of the connections is digital. This means the one LUT is applied to both monitors. I use the dig connection for my main monitor, and the analog connection for the 2nd one.

              So, I calibrate my 2nd monitor (which I use mainly for palettes and email) using the analog connection to my video card. This enables all the color controls on the monitor, so I adjust everything manually. I use Gretag's free DisplayProfile.exe (PC utility) to load the profile for each monitor. It seems to work fine. I load the palette monitor first, then the main monitor second, each having its own profile. I use the digital connection for my main monitor and set it as the system profile. I know the utility works for PC's and with Gretag software. Not sure if it works with XRite software, even though XRite now owns Gretag.

              First, it looks like you have two CRTs, so all the controls on the front of your monitors are probably analog. This allows you to calibrate your monitor to get it mighty close to your target settings, even before anything is written to the video card. So, even if the LUTs are left alone, you should be close to start. Second, you said your video card has two LUTs, so each monitor should remain color managed at all times once they are calibrated and profiled. LUT1 will have curves specific to CRT1, and LUT2 should have its own curves set to correct CRT2.

              Some of this is speculation, since I don't have a similar setup. In fact, I am not sure why DisplayProfile.exe allows me to load separate profiles on my two monitors, since my card has only one LUT, but it is clear that it works. My monitors match fairly closely, and invoking the wrong profile on the wrong monitor definitely whacks it out. So, for whatever reason, it seems effective.

              • 4. Re: Monitor Gamma - How does it get set?
                Lou Dina Level 3
                I didn't answer you question about the color temp.

                You have CRTs, and so you probably have all the controls to calibrate your monitor, independent of the video card. Good CRTs have a lot of control of the RGB guns, contrast, brightness, etc. So, if you wanted, you could calibrate your monitor and never bother profiling it. With a CRT or high end LCD, you can get things very close without writing anything to the video card. That is ideal, since now your video card only has to make very minor adjustments. So, your color is being adjusted using the analog controls on your CRT during the calibration process. Fine tuning is done in the LUT.

                It's kind of like golfing with a full bag of clubs instead of a putter only. The woods and irons get you close (analog calibration), and you use the putter for the final finesse (final tweaks to the video card). Unfortunately, I'd golf just as well with either a putter or a driver and no other clubs. I'm that bad. I play once every 5 years, whether I need to or not!
                • 5. Re: Monitor Gamma - How does it get set?
                  Level 1
                  I did not know that Firefox had a color management plugin. That's great news. I can add it to the 30 plus or minus other plugins that I use. I will definitely check into this.

                  Now that I think of it, my main monitor does have separate red, blue, and green controls. And that actually takes the place of setting the color temp at the standard values of 6500, 5000, etc.

                  So I can just keep doing like you said and get Monitor 2 as close as I can thru the calibration. I don't think that DisplayProfile.exe is available any longer. But there is a "Microsoft Color Control Panel Applet" available since SP2 that supposedly handles two profiles. I'm going to check into this as well.

                  Thanks for all the help! I do appreciate the time you spent explaining this.
                  • 6. Re: Monitor Gamma - How does it get set?
                    Lou Dina Level 3
                    DisplayProfile.exe is available at the following link as a free download. Only works on PCs:


                    • 7. Re: Monitor Gamma - How does it get set?
                      Ramón G Castañeda Level 4
                      Kyle / Lou.

                      Color management in Firefox 3.x (currently 3.0.5), Mac or Windows, can be activated without the need of an add-on or plug-in. The add-on or plug-in is just a convenience.

                      To enable color management type about:config in the address bar, where you normally type a URL. You'll get a dialog box asking you to promise you're going to be careful. Then type gfx.color_management in the Filter field at the top of the the screen and enable it to look like this:

                      gfx.color_management.enabled; user set boolean true

                      Close the window or tab, and you're done.
                      • 8. Re: Monitor Gamma - How does it get set?
                        Lou Dina Level 3
                        Thanks, Ramon. I wasn't aware of that. I wonder why they caution us to be careful? That sounds ominous. Hopefully, it is merely a caution about screwing up color by the uninitiated, rather than a software or bug type caution.


                        In case you are interested, Xrite also has another free download called Calibration Tester, which displays the actual curve adjustments written to your video card after profiling and calibration.


                        They don't make these downloads easy to find. They were listed under the ProfileMaker download.

                        • 9. Re: Monitor Gamma - How does it get set?
                          Level 1
                          Thanks for all the links! It looks like there's alot of options that weren't available a few years ago when I last visited the color management issue. For now, I opted for the Firefox Color Management extension: https://addons.mozilla.org/en-US/firefox/addon/6891, because it allows you to select your profile file on the fly. Otherwise, I would have just made the change to about:config as Ramon mentioned. When I have more time, I'll take a look at the X-Rite options.

                          The about:config warning message is just a generic warning for changing any of the settings in about:config - sort of like changing your registry. You can add a Toolbar Icon for about:config if you add the Mr. Tech Toolkit extension. I recommend this extension because it keeps your extensions from breaking when you update Firefox to the newest version - even if said extension hasn't been updated yet.
                          • 10. Re: Monitor Gamma - How does it get set?
                            Lou Dina Level 3
                            Thanks for the Firefox info, Kyle.

                            After our discussions, I had some questions regarding the ability of my video card to retain LUT data for two different monitors, so I played with Calibration Tester (CT) and DisplayProfile (DP).

                            Displaying both programs in my main monitor window (which is the one I use for critical color and tonal evaluation), I set DP for my main monitor profile. CT showed the curves written to the LUT for that monitor. Then, I moved both DP and CT so they were displayed in my secondary monitor (used mainly for palettes, email, etc). I set my secondary monitor profile using DP, and viewed the LUTs with CT. Definitely different curves. The nice thing is that invoking the profile for my secondary monitor had zero effect on my main monitor. DP and CT both seem to affect only the monitor in which they are currently displayed, and not the other.

                            Moving the CT window back and forth between the two monitors, shows that the proper LUT curves remain loaded and properly dedicated to each monitor. That had been my experience long ago, but I wanted to verify it. What I find interesting is that I have a single LUT in my video card (or at least I think I do). Hey, it works.

                            • 11. Re: Monitor Gamma - How does it get set?
                              Ramón G Castañeda Level 4
                              >I wonder why they caution us to be careful? That sounds ominous.

                              Just because "about:config" gives you access to a zillion gazillion bazillion settings. :D

                              The warning is not specific to colors or color management. Just a note of caution not to go crazy changing things. B)

                              I use it to enable all turbo and acceleration options in Firefox too:

                              Make Firefox SCREAM!

                              1.Type about:config into the address bar and hit return. Scroll down and look for the following entries:


                              set "browser.turbo.enabled" to "True"

                              Normally the browser will make one request to a web page at a time. When you enable pipelining it will make several at once, which really speeds up page loading.

                              2. Alter the entries as follows:

                              Set network.http.pipelining to true

                              Set network.http.proxy.pipelining to true

                              Set network.http.pipelining.maxrequests to some number like 30. This means it will make 30 requests at once.

                              3. Lastly right-click anywhere and select New-> Integer. Name it nglayout.initialpaint.delay and set its value to 0 . This value is the amount of time the browser waits before it acts on information it receives.

                              Restart the browser to enable changes.

                              NOTE: you need to restart Firefox to enable color management too.
                              • 12. Re: Monitor Gamma - How does it get set?
                                Level 1
                                Lou, are you sure your Parhelia has just one lut? I just googled it and it looks like Parhelias have two luts - plus it sounds like you can't use two profiles with one lut? Do you have the oldest Parhelia? Otherwise, I think you would have two luts.

                                Thanks for reminding me about that Ramon. I forgot to reset those pipelining settings after I reinstalled Firefox a couple weeks ago. It was set on 4 maxrequests.
                                • 13. Re: Monitor Gamma - How does it get set?
                                  Lou Dina Level 3

                                  Thanks for the Firefox tips. I will check them out.

                                  Kyle, I'm fairly certain my Parhelia has just one LUT. It is a rather old card, a Parhelia 128 MB AGP card. When I originally bought this card, I had this discussions with Matrox and they told me it only had one LUT. Hey, I could be wrong. It would certainly explain how two different monitors can have their own individual curves and remain properly calibrated.
                                  • 14. Re: Monitor Gamma - How does it get set?
                                    Lou Dina Level 3

                                    I set all the Firefox parameters as you suggested. However, I was unable to find: set "browser.turbo.enabled" and set it to "True"

                                    I just didn't see it in the list.

                                    • 15. Re: Monitor Gamma - How does it get set?
                                      Ramón G Castañeda Level 4
                                      Lou, <br /> <br /> Did you try typing browser.turbo in the Filter field at the top of the window? <br /> <br /> That should bring it up: <br /> <br />c <a href="http://www.pixentral.com/show.php?picture=1tNtueujU1QxunYIZcHSoTSjKz4g4" /></a> <img alt="Picture hosted by Pixentral" src="http://www.pixentral.com/hosted/1tNtueujU1QxunYIZcHSoTSjKz4g4_thumb.jpg" border="0" />
                                      • 16. Re: Monitor Gamma - How does it get set?
                                        Ramón G Castañeda Level 4
                                        Sorry about Pixentral breaking the forum margins. It does that when the image is considerably wider than tall. :/
                                        • 17. Re: Monitor Gamma - How does it get set?
                                          Lou Dina Level 3
                                          No such field comes up when I type that. My list simply does not have that statement!!

                                          Can I create it?

                                          I'm not very experienced with Firefox, so I don't want to mess it up.

                                          Thanks, Lou
                                          • 18. Re: Monitor Gamma - How does it get set?
                                            athegn Level 2

                                            Thank you for the speed up tips.


                                            Try this link:-

                                            • 19. Re: Monitor Gamma - How does it get set?
                                              Lou Dina Level 3
                                              Thanks for the link, athegn. My Firefox browsing is definitely a lot faster. Thanks, Ramon.

                                              • 20. Re: Monitor Gamma - How does it get set?
                                                Ramón G Castañeda Level 4

                                                Thanks for that most interesting link.
                                                • 21. Re: Monitor Gamma - How does it get set?
                                                  Ramón G Castañeda Level 4

                                                  Glad it worked for you.

                                                  As for the browser.turbo thing, my copy of Firefox 3.x just picked it up from my Firefox 2.x preferences when I upgraded to 3.x. It's been a long time, but it is indeed possible that I just created it myself following some instructions, but I don't recall doing so.
                                                  • 22. Re: Monitor Gamma - How does it get set?
                                                    Lou Dina Level 3
                                                    Sorry for the firefox questions (I know this is the color management forum). I added an entry to the about:config file and accidentally set it to "string" instead of "boolean". I cannot seem to change the type to boolean or delete the entry so I can reenter it. If I click the "modify" menu item, it assumes I want to enter a new string. I don't; I want to change the type.

                                                    How to I accomplish this?

                                                    Thanks, Lou
                                                    • 23. Re: Monitor Gamma - How does it get set?
                                                      Lou Dina Level 3
                                                      I think I figured it out. Hit "Reset" for that line item, then restart Firefox.

                                                      • 24. Re: Monitor Gamma - How does it get set?
                                                        Level 1
                                                        Yeah, thanks for that Firefox speed up link. There were alot of settings there I didn't know about.

                                                        At dslreports.com, they have alot of tools for testing speed: http://www.dslreports.com/tools. You can create an account and save your test results. This Tweaking FAQ is really thorough, but it's alot of work to change a couple of settings: http://www.dslreports.com/faq/tweaks. The most important are RWIN and MTU. It gets complicated. I think it has to do with the size of the packets. These are usually optimized for slower connections. So if you have broadband, it supposedly helps alot to fix these settings. If you take the Tweak Test on the Tools page, it will tell you your current RWIN and MTU. Then to fix it, you have to install their DrTCP utility: http://www.dslreports.com/drtcp.

                                                        One more thing that speeds things up is the Microsoft TweakUI tool: http://www.microsoft.com/windowsxp/Downloads/powertoys/Xppowertoys.mspx. The Mouse > Menu Speed setting changes how fast your menu scrolling goes. This one setting makes the biggest difference I think. The faster menu scrolling creates the illusion of a snappier machine. The default setting is way too slow.