On Sun, Mar 28, 2004 at 02:38:12PM -0500, John Culleton wrote:

I find that my current monitor (Orion 17 inch OC-17DB0725) has adjustments for brightness and contrast but none for gamma. The venerable Gimp User Manual (GUM) offers instructions for making at least a crude Gamma adjustment. But my monitor has no such adjustment. and when I load the file recommended by the GUM I find that my monitor is at the high end of the scale for gamma.

The best is to adjust the gamma within the Xfree software. There is an application called kgamma and a plugin for gkrellm to do such an adjustement.

You can alsao use lprof to create a profile for your monitor. lprof allows you to have a separate gamma for each of the RGB channels. Then you can use this profile with the 'color proof' filter within the Gimp.

Is there a monitor at a reasonable cost, a few hundreds of dollars, that allows for adjustment of gamma? Bearing in mind the limitations of Gimp in the color management area, what is suggested? I just want to get things close enough that what I send to the printer will bear some relationship to what I see on the screen in Gimp, allowing for (of course) the conversion to CMYK at some point.

Hi,

John Culleton writes:

I find that my current monitor (Orion 17 inch OC-17DB0725) has adjustments for brightness and contrast but none for gamma. The venerable Gimp User Manual (GUM) offers instructions for making at least a crude Gamma adjustment. But my monitor has no such adjustment. and when I load the file recommended by the GUM I find that my monitor is at the high end of the scale for gamma.

You could use the gamma display filter to get gamma correction for free. With a little extra hacking, you'd get full monitor calibration based on ICC color profiles.

Sven

Hi,

John Culleton writes:

KGamma for some reason was not included on my LInux Slackware 9.1 system so I downloaded the Kgraphics 3.2 package and am compiling it as I write this.

Any text editor to edit your XF86Config would have been sufficient. But then, it's questionable if a general Gamma adjustment on the X server level is such a good idea at all. However if you are seeking for a monitor to do gamma correction, then setting the gamma adjustment on the X server is probably exactly what you want to do.

Sven

[This is personal experience from amateur, so direct instead of list reply]

john@wexfordpress.com (2004-03-28 at 1438.12 -0500):

Is there a monitor at a reasonable cost, a few hundreds of dollars, that allows for adjustment of gamma? Bearing in

Doubt so, but you can get the adjustment via relatively supported videocard (I tried Matrox and ATI with Xfree86 drivers) and tools to tweak the LUT, look up table (xgamma, ie). Speaking about monitors, you can get CRTs with good quality for that price. They should let you select colour temperatures and come with their own profile.

Check the pro range of known brands, probably the 19 and 21 inches sizes only. Three years ago 17 inches was pro too, now that size is crowded by TFTs (*1). Then download all the manuals you can find to inspect what they do. Matching will not be perfect, but you will be safer than with a "go figure how it behaves" monitor.

For the past six or seven years I used Hitachi, CM641ET and CM643ET, both 17 inches (both same specs, they just changed the name, I think), nice quality. But they are leaving that market and going for TFTs now. So some months ago I got a Philips 109P40 for a bit more than 300 euros.

It comes with 9300K, 6500K, 5500K and sRGB presets, allows mid-high resolutions at high refreshes (using 1280*960 at 100Hz at this moment), and the target market is CAD and DTP. It even has an extra input, just in case you need to plug two computers or you have a workstation that uses BNC instead of the typical 15 pin D-Sub. I wanted it a bit for colour quality, and a lot for the flicker free with reasonable resolution, my usage is non pro, but is impossible to get a monitor in which flicker free is not tied to nice tube and lots of controls.

I also checked Hitachi, but they are going out of the CRT field as I said, NEC (fine), Mitsubishi (fine), Sony (expensive), Eizo (also expensive), Iiyama (fine), LaCie (they rebrand others, and add some things). Most of them are basicaly *tron tubes (Trinitron, Diamontron, Whatevertron or just "this monitor uses aperture grille tube"). The two lines that cross the screen are weird the first days, or when you try to concentrate in that area of screen. The *tron mask was also a bit strange for me, cos I was used to the Hitachi tubes, which provided really sharp images with their own technology.

If you can go to the shops and see the monitors working, that would be the best. I did that for the Hitachis, and I was really happy with them. With the Philips it was a different story, now shops go for flashy TFTs so I was unable to check a real model in shops around here, and had to buy by phone a bit blindly.

Good luck shopping. :]

*1: Personally I only like them for pure text processing due the lack of flicker and reduced weight, but hate them for weird 1280*1024 resolution some have, lack of high resolutions (funny to find 1600*1200 or 1400*1050 in laptops but rarely in desktop TFTs, LaCie has one but expensive) and the varying colour response. I still have to find someone that can prove the gamut is above CRTs, last I read was that a medical targeted monitor with a price over a thousand was approaching 90% of NTSC range, if my memory does not fail. The mag company I know go with CRTs, and I agree with the friend I have there: "not yet, maybe in the future, if colour is more important than space, buy CRTs".

GSR

famrom@infernal-iceberg.com (2004-03-29 at 1424.48 +0200):

[This is personal experience from amateur, so direct instead of list reply]

Obviously not. Never start a reply while sleepy and never hit send before checking the field one more time. *hit wall with head*

GSR

Le 29.03.2004 01:46, John Culleton a écrit :

On Sunday 28 March 2004 04:15 pm, Jean-Luc wrote:

On Sun, Mar 28, 2004 at 02:38:12PM -0500, John Culleton

wrote:

The best is to adjust the gamma within the Xfree software. There is an application called kgamma and a plugin for gkrellm to do such an adjustement.

KGamma for some reason was not included on my LInux Slackware 9.1 system so I downloaded the Kgraphics 3.2 package and am compiling it as I write this.

I had no luck with LProf and sent an inquiry to the authors. Whenever I tried to load a file it just quit suddenly with no error message.

Is Gamma adjustable on monitors less than $1,000 US?

In fact, you don't adjust the gamma of the monitor, you tune the window manager, the whole xfree or the application to match the gamma of your monitor. The gamma of the monitor is the transfer function of the electron beams of your monitor. It describes the non-linear relation between the pixel values and the monitor luminance.

Luminance = (pixelvalue/255)^^gamma

As an example, you will find attached what is such a transfer function for several value of gamma.

General, the commonly admited value of gamma for PC is 2.2, the value for a MAC is 1.8 and a liear transfer function will gives 1.

There is also an other setting you have to take care of: it is the colour temperature of your display. There is for most the display the choice of different colour temperature. The default value is 9500K which gives very cold colours (too much blue). This is perfect for office work. For digital photo processing a colour temperature of 6500K if available is more suitable.

--
John Culleton

--
Regards
- Jean-Luc

Hi,

do you consider global gamma adjustment useful at all? It means that everything on your screen, inlcuding the GUI and also the content displayed in your web-browser, image viewer, PDF viewer ... is gamma-corrected. IMO this is questionable since most software assumes an uncorrected display. Shouldn't gamma correction take place at the application level instead so that it is only applied to images that specify a gamma correction?

Please excuse my ignorance, I am trying to understand what's really needed for professional image manipulation and so far I understood that global gamma correction is not desirable.

Sven

V Po 29. 03. 2004 v 16:27 +0200 píše Sven Neumann:

Please excuse my ignorance, I am trying to understand what's really needed for professional image manipulation and so far I understood that global gamma correction is not desirable.

As a metatheme author I think it is very desirable to have a global gamma correction. Same reasons apply to the widget theme as it does for displaying images.

Great example is the Industrial gtk theme that uses a very light gray that on some system simply looks white. Apple has a nice system-wide calibration in OSX called ColorSync I believe.

cheers

Le 29.03.2004 16:27, Sven Neumann a écrit :

Hi,

do you consider global gamma adjustment useful at all? It means that everything on your screen, inlcuding the GUI and also the content displayed in your web-browser, image viewer, PDF viewer ... is gamma-corrected. IMO this is questionable since most software assumes an uncorrected display. Shouldn't gamma correction take place at the application level instead so that it is only applied to images that specify a gamma correction?

The best solution would be to have the whole desktop managed.

But, as most of the applications are not aware of the gamma you setup in Xfree, I my opinion, the best is to do the correction at the application level (as does scribus for instance).

Please excuse my ignorance, I am trying to understand what's really needed for professional image manipulation and so far I understood that global gamma correction is not desirable.

In the case of professional use, most of the image processing stations will have a dual-head system. One display, calibrated (profiled) to display the picture you are working on (mostly a CRT or a dedicated plasma type, only few -- expensive -- TFT are able of a right contrast/ gamma/colour handling) and a second one for the palettes, tools and so (and other applications like web browser). This one is mostly a relatively cheap TFT.

--
- Jean-Luc

Sven

Hi,

"Jean-Luc Coulon (f5ibh)" writes:

The best solution would be to have the whole desktop managed.

But, as most of the applications are not aware of the gamma you setup in Xfree, I my opinion, the best is to do the correction at the application level (as does scribus for instance).

Huh? If you set your gamma correction on the X server than everything on your screen is gamma corrected, completely transparent to the application. What do you mean by "an application being aware of the gamma you setup in Xfree" ?

Sven

Le 30.03.2004 16:26, Sven Neumann a écrit :

Hi,

"Jean-Luc Coulon (f5ibh)" writes:

The best solution would be to have the whole desktop managed.

But, as most of the applications are not aware of the gamma you setup

in Xfree, I my opinion, the best is to do the correction at the application level (as does scribus for instance).

Huh? If you set your gamma correction on the X server than everything on your screen is gamma corrected, completely transparent to the application. What do you mean by "an application being aware of the gamma you setup in Xfree" ?

If you setup a gamma of say 2.2 in Xfree, you will get most of the appllications wrongly displayed as they are not designed to support this setting.

--
- Jean-Luc

Sven

sven@gimp.org (2004-03-29 at 1627.13 +0200):

do you consider global gamma adjustment useful at all? It means that everything on your screen, inlcuding the GUI and also the content displayed in your web-browser, image viewer, PDF viewer ... is gamma-corrected. IMO this is questionable since most software assumes an uncorrected display. Shouldn't gamma correction take place at the application level instead so that it is only applied to images that specify a gamma correction?

Well, I have global settings. What is more, the monitor has controls like color temperature, brightness or contrast that affect the global look, and no way to avoid that, at most you can ignore it and say yours is fine and the rest not. Anything that cares about providing decent data looks fine (some photo websites, ie) and those that do not care look fine (when they are lucky) or normally crap.

I have a wm menu entry to quickly change gamma, to get a rough idea of what others can see or try to see as they created the thing I am looking at. So far this has served me well, I know it is not perfect but it is way better than seeing weird things or wasting time convincing everyone to make apps that pay attention to colour issues... and then convince every creator to do the same. It would be great, but until then, each one has to find solutions.

The common problem I have is when trying to show something I did and the monitor used is completly misadjusted or really damaged or both. It is a real pain to pass most of the time saying "well, this shadow here has this and that details, but this monitor only shows black, so please imagine them" instead of talking about other more important things in the image. Similarly goes for TFT, but in that case it normally is also includes "look from here if you want to see it a bit better". :]

Please excuse my ignorance, I am trying to understand what's really needed for professional image manipulation and so far I understood that global gamma correction is not desirable.

Maybe you are confusing the completly fucked up monitors some people have with a known config and extra control in apps. I have default app configs targeted at the default monitor config I use, and accept that for quick changes they will look rare. If I pass too much time jumping I have no problem cos I created the menu in such way that I can change most of the interface to match gamma, I just have to create the extra versions required.

So I am not gamma correcting my interface for fun, but more like putting it in a generaly accepted default and doing it with no extra CPU load (video card LUTs). And above all notice that gamma correction will not solve problems like out of gammut or colour shifts, it is part not the final solution.

Related side note: Do libs like gtk+, freetype / fontconfig, etc pay attention to colour management issues? At least the basic gamma? Globally? Per monitor? I think they do not at all and they should in some cases (adapt to given monitor, provide correct results), but I guess they caused the general impression gamma is non important except for professional image manipulation. I would be very happy to get professional colour matching in image apps, and at least the bare minimums for all the apps.

Conclusions: monitors and video cards should be adjusted at least basically (that includes gamma and is an user task), normal apps should care a bit (AA fonts, ie), and image manipulation apps should care a lot more. It is a progresive thing.

GSR

Hi,

GSR - FR writes:

Conclusions: monitors and video cards should be adjusted at least basically (that includes gamma and is an user task), normal apps should care a bit (AA fonts, ie), and image manipulation apps should care a lot more. It is a progresive thing.

Nice reply, but you didn't answer my question.

Sven

sven@gimp.org (2004-03-31 at 2011.13 +0200):

Conclusions: monitors and video cards should be adjusted at least basically (that includes gamma and is an user task), normal apps should care a bit (AA fonts, ie), and image manipulation apps should care a lot more. It is a progresive thing.

Nice reply, but you didn't answer my question.

Let try sorter: the question was "do you consider global gamma adjustment useful at all?" and the reply was "yes, not only useful but a basic".

GSR

Le 31.03.2004 22:29, John Culleton a écrit :

On Wednesday 31 March 2004 01:34 pm, GSR - FR wrote:

sven@gimp.org (2004-03-31 at 2011.13 +0200):

[.. destructive compression ..]

I am busy window shopping on Ebay etc. If the monitor has an adjustment for color temperature is that the equivalent of adjustable gamma? Or are they different parameters?

No, it is an other thing. There are 4 important parameters:

- white point and black point, both are adjusted with brightness and contrast settings
- colour temperature: a tungstene light has a colour temperature of about 3200K, a flash lamp gives you a colour temperature of about 5500K, sunny daylight is about 6500K. With high colour temperatures, the colour cast is blueish, with low colout temperature, it is redish. Normal office work dispaly uses color temperature as high as 9300K. For photography, 6500K is better.
- gamma : this is the non linear function transfer of the brightness given by the display as a function of the pixel value.

-- - Jean-Luc

--
John Culleton

john@wexfordpress.com (2004-03-31 at 1529.45 -0500):

I am busy window shopping on Ebay etc. If the monitor has an adjustment for color temperature is that the equivalent of adjustable gamma? Or are they different parameters?

They are different, it sets how white will look, 5500K is yellowish, 9300K is blueish, and 6500 can be considered middle ground (sRGB uses this one, iirc).

GSR

Hi,

GSR - FR writes:

Let try sorter: the question was "do you consider global gamma adjustment useful at all?" and the reply was "yes, not only useful but a basic".

Well, I sortof find it distracting to have the user interface gamma corrected. If I set a reasonable gamma value on my X server, things look washed out and pale. Is that really desirable?

Sven

A little off topic, but the following site has an extreamly useful tutorial on how gamma, contrast, brightness play together and calibration of same. He's windows oriented, but the concepts and tests are the same.

http://www.normankoren.com/makingfineprints.html

----- Original Message ---

Just in case this wasn't clear in my last message, I'll expand on a few points. You can implement either or both of calibration and profiling.

Having systems calibrated to a common standard means that you don't _have_ to worry about ICC profiles etc IF ALL YOU'RE DEALING WITH IS RGB DATA IN THE COLOUR SPACE REPRESENTED BY THAT CALIBRATION. Thus with the Gimp in its current form, calibration is important (it's the only thing available!).

But if you want _accurate_ colour you need to implement profile support (e.g. building on top of lcms) including dynamic conversion from an image's colour space to the display system's profile. With full profile support it doesn't matter what the user's system is calibrated to (e.g. weirdarse 1.8 gamma). If an image's data is in sRGB the colours will get converted so that what is displayed on the screen is accurate, even though sRGB has a gamma of 2.2. My systems are calibrated to a gamma close to 2.2, and I can view images in "ColorMatch RGB" (which has a gamma of 1.8) with no problems as the profile conversion takes care of that for me..

Calibration benefits the non-colour-managed applications, but with only limited usefulness. Mac and Windows systems implement both calibration and profiling in an attempt to serve both CM and non-CM applications (and the calibration can help ensure the system is in a reasonable state prior to profiling).

Full profile support is important because the colour response of your inkjet printer, scanner, printing press, etc will probably not match that of your calibrated system, and for accurate work you need a profile describing the colour space of each and to convert between them as required.

I'll shut up for now. ;) Cheers
__
David Burren

sven@gimp.org (2004-03-31 at 2350.03 +0200):

Let try sorter: the question was "do you consider global gamma adjustment useful at all?" and the reply was "yes, not only useful but a basic".

Well, I sortof find it distracting to have the user interface gamma corrected. If I set a reasonable gamma value on my X server, things look washed out and pale. Is that really desirable?

Some time ago I had the same problem than you: I went from default config (or lack of it) to something reasonable (or at least try). Yes, of course, my interface changed at first, so I compensated it but did not go back to unconfigured state. Since, when I have changed video card or monitor, I just had to check their settings, not change the interface all over again. That is what makes it desirable, two properly adjusted hardware sets will give a similar look.

GSR

Hi,

On Thu, 2004-04-01 at 15:00, GSR - FR wrote:

Some time ago I had the same problem than you: I went from default config (or lack of it) to something reasonable (or at least try). Yes, of course, my interface changed at first, so I compensated it but did not go back to unconfigured state. Since, when I have changed video card or monitor, I just had to check their settings, not change the interface all over again. That is what makes it desirable, two properly adjusted hardware sets will give a similar look.

So would it be possible to do a quick tutorial on how to adjust the gamma of ones videocard/monitor combination? If yes, I think it would be nice to have such a tutorial on www.gimp.org.

Sincerely, Brix