A General Question about Monitor Gamma

General Color & Graphics Monitor Calibration & Soft Proofing
1

Hi, first post here. I’m using a Monaco Optix XR to profile a low-cost 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 preffered 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? If that is the case, then why is gamma adjustment reffered to as part of calibration - not profiling?

Thanks alot!
IB

2

You bring up several good points which I’m sure a lot of people would like the answer to.

Your description of “calibration” vs. “profiling” is close but not quite right. The whole process of hardware adjustment and software-showing-colors-to-the-colorimeter is all in the realm of calibration. The “profile” is best thought of as a file that describes (to color-managed programs) what kind of color to expect from a calibrated monitor.

Check out the section on Video cards, LUTs, 8-bits? What IS all this? in the following newsletter article: http://www.colorwiki.com/wiki/Monitors_Part_One

People sometimes get pretty hung up on which gamma setting to choose. Keep in mind that a gamma curve is only going to be applicable in non-color managed programs. If you are viewing your images in Photoshop, PS’s use of the monitor profile will cancel out any Gamma curve. You won’t see any “2.2 more highlight detail” or “1.8 more shadow detail” because PS takes it out of the equation so you’re just seeing “what is.”

You picked a great question for your first post. Keep 'em coming!

3

Thanks Pat. That article helps. I just noticed that you’re the author!

Now I need to figure out how this will play out with my two-monitor setup. I have a Matrox P650 video card - that has two LUTs. Monitor1 is an LCD that I will use as my daily use monitor - and to hold the tools when using Photoshop. Monitor2 is a CRT that will hold the image I’m working on in Photoshop.

What I still am not sure about is if I calibrate/profile (with Optix XR) Monitor1, then calibrate/profile Monitor2… I know that Windows will only use one profile as the default. So when I save the Monitor2 profile, will Monitor2’s calibration info get written to the LUT for Monitor1 as well? In other words, is it possible to have two different LUT calibration settings going at once? Or is that restricted to just one, the same as with the profiles? I don’t mind the fact that Monitors2’s profile will be used on Monitor1. I just wouldn’t want Monitor2’s calibration info also being applied to Monitor1. Does that make sense?

I downloaded the DisplayProfile software for multi-monitor setups. That seems perfect because I really only need one monitor to look good at any one time. In daily use, I would like Monitor1 to be accurate. When working in Photoshop, I would like Monitor2 to be accurate. So DisplayProfile sounds like the answer for me, but I would still like to know the answer to what I asked above, just for my own curiosity. :wink:

4

Which operating system are you on? If on XP you can use a little program called Microsoft’s Color Control Applet. This will allow you to assign a specific profile to a specific monitor. Usually you need to have separate graphics cards in order to have independent calibrations on both monitors - but when you say your Matrox has two LUT’s, then I don’t know, that might work too. You’d have to try it to see.

You could do a search in these forums for anything with the word “applet” and you’ll get some good threads on this subject. Here is one:
[url]http://one.imports.literateforums.com/t/2-monitor-profiles-in-windows-xp/593/1]

Don’t underestimate the value of having both monitors calibrated and matching - even if one is just for tools and such. When you have another monitor in your field of vision that is off-color, it can mess up your eyes’ opinion of what “normal” is. Sometimes it’s worth the extra 20 bucks to get a second hand graphics card somewhere.

5

Warning. Very long post ahead! No questions, except for one very minor question at the end. It seems the more I experimented, the more I answered my own questions. But I wanted to complete this thread - and hopefully, somebody else who’s just getting started with color management, or who’s using the same equipment, will stumble on this and learn something from one of my mistakes or observations. If you see anything that’s inaccurate, please let me know.

So I spent a lot of time on this over the past couple weeks and I’m happy to say that I finally got it locked in. A few years ago, I never thought it would be possible. But right now I’m looking at two monitors side-by-side, one LCD and one CRT, with the same image open in each one, and they look identical. I almost settled for less. The LCD still looked a little washed out compared to the CRT, color temps slightly different. But I went back, spent another couple hours tweaking the profiles. Nudging the software settings oh so slightly, over and over until I nailed it. My persistence paid off! Some observations I made along the way:

  • This wouldn’t be possible in Windows XP without the Microsoft Color Control Applet for Windows XP (or something similar). When I first looked into color management five years ago, you were stuck with one profile in XP. The result was two drastically different displays. I accepted this and moved on. I never revisited color management until now. I had no idea that Microsoft came out with this neat little tool. That changed everything! One small issue, I still have to select one of the profiles as the default in Windows’ Display Properties. That profile will be used as the default profile for Photoshop as well. When I reboot, both monitors startup using the default profile. So I have to open Microsoft Color Control (found in Control Panel) and assign the non-default profile to the non-default monitor. This takes a few seconds.

  • I might be wrong, but I suspect that in order for the two different profiles to work side-by-side, you need either two video cards or a video card with two LUTs - such as the Matrox P650 that I’m using. At the time that I purchased it, I remember reading about the two LUTs and what a cool feature that was. I had no idea what a LUT was. But it sounded like something I might use one day, so I went for it. Now I’m happy I did.

  • The Monaco Optix XR is a great piece of equipment. Five years and it’s still running strong. Of course mine could be off at this point. But I didn’t use it much. And the results are extremely consistent and predictable each time that I use it. So I think that’s saying something. It looks like the ColorEyes Display Pro Bundle uses the same DTP-94 sensor as the Monaco Optix XR. So they can still be had when mine dies off. That’s good news.

  • I think Patrick was right when he commented on the importance of having your two monitor’s profiles match. I read somewhere that when profiling your monitor, it’s best to use the monitor’s native white point - rather than setting it to D65. I think many people do this to avoid banding and artifacting. This may work better for a CRT or high-end LCD. But on my cheap LCD, it wasn’t pretty. The result was very red - 5633 K. Sitting next to the CRT with a nice neutral looking 6500 K, it was very distracting. I couldn’t leave it that way. An interesting point though. Checking each profile’s curve in the X-Rite Calibration (LUT) Tester: xrite.com/product_overview.a … wareID=546 , the profile using the LCD’s native white point showed very little deviation to the curve. The profile using D65 showed much more deviation to the curve. In addition, using D65, it was harder to use the Monaco software to get where I wanted. Judging by the resulting curve, it looked like the software had to jump through some hoops to force the results that I was demanding from my cheapie LCD. So I can see the point of using native white point. It would probably produce less banding as well. But in my case, I couldn’t deal with the results. A clean white was more important to me than a nice curve.

  • Since learning color management, my favorite color is now gray. I’ve become really picky about my grays and whites. If it’s just a couple steps off on one of the color channels, I can tell. There’s just something really satisfying about a nice neutral gray. For my desktop background, I made an image consisting of squares going from pure black to pure white, in two-step increments, 9 rows x 14 columns. This tells me which profile is loaded in each monitor. It’s really obvious if something is off. The grays and whites look awful when the wrong profile is loaded.

  • I learned that it’s a bit tricky to properly calibrate a cheap LCD monitor. At first, I was seeing White Luminosity numbers, measured by the Optix XR, as high as 250 cd/m^2 - with my LG W2252TQ monitor. I thought those numbers had to be wrong. My five-year-old Optix XR must not be compatible with newer LCDs I thought. Well it turns out that the numbers were right. LG advertises this monitor as having a contrast ratio of 1000:1. I suspect that they just put a ridiculously bright backlight in it - and that allowed them to get away with advertising such an inflated number. After much research, it wasn’t easy to find, but I learned how to calibrate this monitor. Since all of the monitor controls are actually software adjustments except for Brightness, leave them alone. Leave Contrast at the default value of 70. Since the Brightness control is tied to the backlight, adjust it to a setting that’s close to the final luminance values you’re looking for. I wanted to match my CRT at approximately Black Lum .20 and White Lum 115. So Brightness value of 45 got me real close to White Lum 115. I didn’t worry so much about the Black Lum, but it was fairly close as well. So after many attempts at profiling, I finally arrived at .15/115.21 for the LCD and .19/115.54 for the CRT. You might think that’s a high White Lum for a CRT, especially if you’re trying to match prints to your display. But that’s not my goal. I’m using my displays for designing websites, which leads to my next point

  • There’s still very little, if any, information available online targeted at calibrating displays for web work. I read that White Lum should be targeted at 85 to 95 cd/m^2 for print work. But what if you’re designing websites? The problem is that, as far as I know, there is no standard to target. And I don’t think there can be, as everybody has his/her display setup differently. So I asked myself “Who’s my audience? How do they have their monitors set?” So I looked at friends’ monitors and it became obvious that most people leave their display at the default settings. So I kept that in mind, tried many different White Lum targets, and settled on White Lum 115 - which is actually low for my equipment. My Compaq CRT outputs about 130 out of the box and my LG LCD outputs about 250 out of the box. But I couldn’t do that to myself. 115 was nice and bright, not washed out, and quite comfortable for daily use. I think the fact that I have a lot of light in the room means that I have to set White Lum higher than normal. This is hardly a pro setup, but I have a standard overhead light using three 40-watt GE Reveal bulbs. A more realistic match to the average user would be standard bulbs - with their yellowish hue. But that would be hard for me to handle. I just have to remember to always use the same bulbs - and always change them when they burn out. In the end, just to be realistic, I’ll probably test my web pages with monitor Contrast jacked all the way up - just to make sure they pass the reality test.

  • The one thing I’m still confused about is my gamma values. When profiling, I used gamma 2.2 in the Monaco software. But when I check gamma using many of the various online visual gamma checking tools and images, I get about 2.4 for the CRT and 2.0 for the LCD. In addition, it doesn’t seem to matter if I am using a color-managed program like Photoshop or a non-color-managed program like Internet Explorer. The results are always the same. Patrick mentions in this thread that gamma 2.2 won’t come into play with color-managed programs, but it will with non-color-managed programs. It’s not working that way for me. Whether I’m in Photoshop, Internet Explorer, Firefox, or even my desktop background, my gamma is always 2.4 for the CRT and 2.0 for the LCD - according to the visual tools. For the record, the gamma tools I’m using are here: brucelindbloom.com/index.html?Vcgt.html . If I get the extra time, maybe I’ll experiment with these. Probably not though. I’m already very happy with what I have.

I think that’s about it. Thanks for listening!
-IB

6

A fabulous post!

I hope people will take the time to read what you say, because you have a very fluid way of explaining all that you looked at and I think the reader will follow it very easily.

Let me highlight some of the comments idbit made:

It IS possible to make two monitors match.

On Windows, it can take a little more work, and he describes it well.

The DTP-94 is the same instrument as the Monaco Optix XR. The ColorEyes Display people still get them from Xrite, and it’s a great instrument. (and you can get them at CHROMiX)

I had to laugh when I read about your newfound appreciation for gray. Back in the film days, when I would take test pictures to analyze new film emulsions, I got to know the best collections of rocks and cement in a 3 block radius of my plant. In the RGB world that is our monitor, grays are made up of all three colors, and our eyes are very good at distinguishing differences in gray. They’re much better at that than, say - comparing a super-saturated magenta to a slightly less saturated version. Yep - gray is your friend.

I have not tried any of the online gamma tests, so I don’t know what to tell you there. Maybe someone else can chime in.

If you have a bright room, 115 is fine. A lot depends on your surround light. 115 in a cave would blast your eyes out for example, but in a bright room, it’s what you need for it to look right.

One thing you didn’t mention learning yet is the power of optical illusions. We often underestimate how much our eyes and brains adjust to what we see and how easily we (re)interpret things as ‘normal’.

Come to think of it, that happens a lot in life, not just in color!

7

Yeah, my room here is pretty bright. When I first began redesigning this website, I had the lights dim - white lum under 100. I was pretty much setup for digital photography. I really got into it and learned alot. That’s when I developed my fondness for gray. I learned how to do manual white balance, using the Canon Raw plugin. And I even went as far as buying a Color Checker chart so I could profile my camera. I even had it measured by… Well, I just looked, it was Chromix that measured it for me - Mike Cummings, that was in 2004. Anyway, my focus was completely photgraphy driven. So when I made my first stab at designing this web page, it looked great to me. Then I checked it at a friend’s house. What a difference! The colors were pathetically undersaturated. It was ugly! It’s no wonder most websites use very saturated colors. So anyway, that’s made me realize that I was going to have to completely reverse my philosophy when it comes to room lighting and ultimately my target white lum. In order to match what 90% of the general public is doing, a bright room and a white lum of 115 is about what gets me there.