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Author Topic: Video Card Drivers  (Read 8178 times)
GBCollins
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« on: May 02, 2006, 07:59:04 PM »
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It appears that in most of the current video card drivers, there is the ability to import a color profile, namely a custom monitor ICC profile.  And then there's the gamma slider, it's native or standard position is one (1).  Who uses this and why?  Nothing looks right if you import a 2.2 gamma profile.  Just wondering........
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61Dynamic
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« Reply #1 on: May 02, 2006, 08:48:27 PM »
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The only people who use these settings are those who want a bad monitor calibration (or don't know any better); LCD or CRT. All the adjustments in there alter the video card's 24-bit LUT which in turn degrades the image before it even reaches the display.

Leave them at the factory defaults and all will be well.
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Serge Cashman
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« Reply #2 on: May 03, 2006, 11:42:16 AM »
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I was wondering about it. I think it's useless. Don't know what they were trying to achieve.
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Loadus
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« Reply #3 on: May 03, 2006, 04:19:52 PM »
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What does the (bad) image look like after the import? Bright?
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GBCollins
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« Reply #4 on: May 03, 2006, 08:48:37 PM »
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What does the (bad) image look like after the import? Bright?
[a href=\"index.php?act=findpost&pid=64400\"][{POST_SNAPBACK}][/a]
If you import a custom monitor profile with a 2.2 gamma into a nVidia driver, the display goes to about 1 gamma too bright.  On the other hand, import Srgb and it goes dark about 1 gamma from "normal".
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Loadus
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« Reply #5 on: May 03, 2006, 08:59:45 PM »
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kewl. Sounds like it's trying to linearize the LUT>CRT gamma. Wanna hear a funny story? I'm actually one of those people who prefer to work in that "bad" calibration mode (only made with Spyder2, not manually).
« Last Edit: May 03, 2006, 09:01:05 PM by Loadus » Logged

61Dynamic
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« Reply #6 on: May 04, 2006, 12:05:09 AM »
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kewl. Sounds like it's trying to linearize the LUT>CRT gamma. Wanna hear a funny story? I'm actually one of those people who prefer to work in that "bad" calibration mode (only made with Spyder2, not manually).
[a href=\"index.php?act=findpost&pid=64420\"][{POST_SNAPBACK}][/a]
Actually it's not linearizing anything. It's applying a profile that is not designed to work with it.

If you set a custom gamma in the calibration software, then you are not working with a profile as badly skewed as what you'd get by simply changing the video card driver since part of the process involved with the calibration software is creating a custom profile for the display.

Setting the gamma to a LCDs native gamma would net you the best results but altering the gamma in the calibration software will work well enough for all but the most stringent situations (there are a few much bigger issues to worry about first).

With CRT's the gamma can be set to whichever gamma you prefer without degradation since the CRT is set with analog controls. A LCD is set when it's built.
« Last Edit: May 04, 2006, 12:07:23 AM by 61Dynamic » Logged
Loadus
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« Reply #7 on: May 04, 2006, 05:01:06 AM »
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... It's applying a profile that is not designed to work with it ...

Strange - sounds like it's screwing things up in the LUT. Well anyways. My TFT looks really funky to most people, since my calibration with Spyder is not done for 2.2 gamma but for 1.0. And to make things worse, I use CIE 1931 D65 G1.00 working space. Yeah, the best moments are when people who are not accustomed to the bright gamma and the sci-fi colors of CIE try to edit photos on it. There's a lot of screaming and bloodspill. For webwork I use the basic 2.5 Gamma (of course).
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61Dynamic
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« Reply #8 on: May 04, 2006, 10:59:41 AM »
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Your working in a linear color space and using an out-dated device-independant color space... And then you use a non-standard gamma for web-editing.  What benefit could you believe you are gaining from working that way?
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Loadus
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« Reply #9 on: May 04, 2006, 03:54:30 PM »
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Well, the HSL adjustments behave very differently on portrait photos (ie. no green/orange cast on shadows) and pretty smooth USM as well. Outdated colorspace maybe, but large. And if Kodak derives it's ROMM ICC from that space, it can't be that outdated. And 2.5 gamma is the natural gamma of a CRT monitor, very good for web images.
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Serge Cashman
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« Reply #10 on: May 04, 2006, 04:46:40 PM »
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Does anybody know how to measure and set Native gamma with a Spyder2 Pro? Native wb - no problem. But where's Native Gamma?
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bruce fraser
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« Reply #11 on: May 04, 2006, 04:52:54 PM »
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With CRT's the gamma can be set to whichever gamma you prefer without degradation since the CRT is set with analog controls. A LCD is set when it's built.
[a href=\"index.php?act=findpost&pid=64435\"][{POST_SNAPBACK}][/a]

Actually, no. The analog controls in a CRT let you set the white point by changing the gain and (sometimes) bias of the R, G, and B voltage amplifiers. Adjusting gain and bias to set white and black points for each channel does have an effect on the gamma, but doesn't let you set it to a target value.

Gamma in this context is the relationship between input power and output brightness, so it depends on the absolute voltages and the electro-chemical properties of the phosphors. The only way to set the gamma on a CRT to a specific value is to tweak the LUTs in the video card. Calibrating to native gamma offers the same benefits on a CRT as it does on an LCD.
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Serge Cashman
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« Reply #12 on: May 04, 2006, 05:00:58 PM »
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Interesting. Is that why you'd still need an LUT loader even with DDC capable monitors? Or DDC can adjust gamma as well?
« Last Edit: May 04, 2006, 05:01:54 PM by Serge Cashman » Logged
bruce fraser
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« Reply #13 on: May 04, 2006, 05:02:13 PM »
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...if Kodak derives it's ROMM ICC from that space, it can't be that outdated....[a href=\"index.php?act=findpost&pid=64501\"][{POST_SNAPBACK}][/a]

Kodak derived ROMM (now ProPhoto RGB) from CIE LAB 1976, which was built to reduce the severe non-linearity of CIE XYZ (1931), so the relationship is pretty distant. (ROMM stood for Reference Output Medium Metric—ROMM RGB was designed to translate into and out of Lab with as little quantization error as possible, using an idealized print medium with a dMax of 2.8 as the reference.)

XYZ is still useful for many things (it serves as the Profile Connection Space for all matrix ICC profiles), but using it as a working space for editing is, putting it gently, idiosyncratic, since changing the numbers by the same increment will produce wildly different degrees of visual change depending where in the space those numbers are located. That's the problem Lab was designed to address....
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Schewe
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« Reply #14 on: May 04, 2006, 05:06:26 PM »
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my calibration with Spyder is not done for 2.2 gamma but for 1.0. And to make things worse, I use CIE 1931 D65 G1.00 working space.
[a href=\"index.php?act=findpost&pid=64462\"][{POST_SNAPBACK}][/a]

You don't know that Timo fellow do you. . .the one that claims that gamma 1.0 is better than 2.2?

::ducking::

:~)
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bruce fraser
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« Reply #15 on: May 04, 2006, 05:07:18 PM »
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Interesting. Is that why you'd still need an LUT loader even with DDC capable monitors? Or DDC can adjust gamma as well?
[a href=\"index.php?act=findpost&pid=64510\"][{POST_SNAPBACK}][/a]

DDC can adjust gamma on those LCD displays that have internal LUTs, usually with greater bit depth than those on the video card. For other displays, Windows systems need a LUT loader. Mac OS has automatically loaded the 'vcgt' tag from the display profile since around the days of OS7. There's still no unified way to do so on Windows. Reportedly Vista will offer OS-level support for vcgt tags.
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Loadus
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« Reply #16 on: May 04, 2006, 05:09:27 PM »
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Cool. Well, I'll continue to do my idiosyncratic photos, since that solved many issues of processing Bayer images.   I'm just so lazy to change it to anything else ...
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Serge Cashman
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« Reply #17 on: May 04, 2006, 05:16:39 PM »
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DDC can adjust gamma on those LCD displays that have internal LUTs, usually with greater bit depth than those on the video card. For other displays, Windows systems need a LUT loader. Mac OS has automatically loaded the 'vcgt' tag from the display profile since around the days of OS7. There's still no unified way to do so on Windows. Reportedly Vista will offer OS-level support for vcgt tags.
[a href=\"index.php?act=findpost&pid=64514\"][{POST_SNAPBACK}][/a]
Thanks a lot. That was confusing me for a while.
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61Dynamic
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« Reply #18 on: May 04, 2006, 05:30:14 PM »
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Actually, no. The analog controls in a CRT let you set the white point by changing the gain and (sometimes) bias of the R, G, and B voltage amplifiers. Adjusting gain and bias to set white and black points for each channel does have an effect on the gamma, but doesn't let you set it to a target value.

Gamma in this context is the relationship between input power and output brightness, so it depends on the absolute voltages and the electro-chemical properties of the phosphors. The only way to set the gamma on a CRT to a specific value is to tweak the LUTs in the video card. Calibrating to native gamma offers the same benefits on a CRT as it does on an LCD.
[a href=\"index.php?act=findpost&pid=64509\"][{POST_SNAPBACK}][/a]
Ah! I had a correction all typed up and you had to go and beat me to it. Time researching, typing, and proof-reading all down the crapper.  I stand corrected.

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Well, the HSL adjustments behave very differently on portrait photos (ie. no green/orange cast on shadows) and pretty smooth USM as well. Outdated colorspace maybe, but large. And if Kodak derives it's ROMM ICC from that space, it can't be that outdated. And 2.5 gamma is the natural gamma of a CRT monitor, very good for web images.
[a href=\"index.php?act=findpost&pid=64501\"][{POST_SNAPBACK}][/a]
As Bruce pointed out, gamma is set by the video card LUTs. In Windows, the native gamma is 2.2 and Mac is 1.8. So if your intention is for web output, you should be working with a 2.2 gamma since it is the gamma for the majority of systems out there. Setting your calibration to 2.5 can give you a good amount of difficulty trying to match a sRGB jpg to a gif to a Hexadecimal color in a CSS file. Since color management is practically nonexistent on the web, things need to be edited for the least common denominator.
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Loadus
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« Reply #19 on: May 04, 2006, 06:35:31 PM »
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... Since color management is practically nonexistent on the web ...

Yes, well, there you have it. sRGB is the Windows' colorspace. True. Majority of the CRT monitors out there are uncalibrated. True. The gamma of those monitors is 2.2. Major false - it's 2.5, sometimes even deeper in the black end. This is about to change however, since the new LCDs are bringing desktops closer and closer to 2.2 - I have come across some oddballs though, like the BenQ FP731 that doesn't seem to be neither 2.2 nor 1.8 but something like 1.6 (?).
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