Re: [Gimp-user] Re: Re: Re: Monitor for Gimp
Hi, David Burren <[EMAIL PROTECTED]> writes: > Does that description clear up anything for you? Yes, that was a very helpful explanation. Thanks a lot. > Lack of support for this stuff in the Gimp et. al. is the main > reason I moved to Macs (I have an IT background, but these days > work as a professional photographer). I haven't given up the Gimp > entirely yet, but its getting less and less use over time. Since we have display filter modules in GIMP 2.0 and there's a color proof display filter module already, it's probably less than an hour work to add a display filter that uses lcms to color-correct for the monitor. The only issue with this is that display filters are not yet nicely integrated into the workflow. You have to manually select them for every display you open. This is something that I'd like to see improved for GIMP-2.2. If there was a standard on where to look for the monitor ICC profile and such, that would certainly make things easier. There's a newly created mailing-list on freedesktop.org that deals with this stuff. If you want to join this list, please see http://pdx.freedesktop.org/cgi-bin/mailman/listinfo/openicc Sven ___ Gimp-user mailing list [EMAIL PROTECTED] http://lists.xcf.berkeley.edu/mailman/listinfo/gimp-user
Re: [Gimp-user] Re: Re: Re: Monitor for Gimp
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 ___ Gimp-user mailing list [EMAIL PROTECTED] http://lists.xcf.berkeley.edu/mailman/listinfo/gimp-user
Re: [Gimp-user] Re: Re: Re: Monitor for Gimp
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 - From: "Sven Neumann" <[EMAIL PROTECTED]> To: "GSR - FR" <[EMAIL PROTECTED]> Cc: <[EMAIL PROTECTED]> Sent: Wednesday, March 31, 2004 14:50 Subject: Re: [Gimp-user] Re: Re: Re: Monitor for Gimp > Hi, > > GSR - FR <[EMAIL PROTECTED]> 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 > ___ > Gimp-user mailing list > [EMAIL PROTECTED] > http://lists.xcf.berkeley.edu/mailman/listinfo/gimp-user > ___ Gimp-user mailing list [EMAIL PROTECTED] http://lists.xcf.berkeley.edu/mailman/listinfo/gimp-user
Re: [Gimp-user] Re: Re: Re: Monitor for Gimp
John Culleton <[EMAIL PROTECTED]> wrote: > > So how do I determine which monitors, if any can have adjustable > Gamma? BTW I specified 3.0 gamma in my XF86Config file but I can > spot no difference in the test files. So my current Orion monitor > (17") does not seem to adjust. Monitors typically don't have adjustable gamma. The gamma is a factor of the behaviour of the phosphors/etc and isn't adjustable (except maybe as a side-effect of manipulating overall brightness and contrast). But the native gamma of the monitor will change over time as it ages. However, most video cards have a lookup table (LUT) which can be used to statically transform each of the R/G/B components. By default this LUT is loaded by the X server with a linear transform (a gamma of 1.0) and the effective gamma of your video system is the combination of that and the native gamma of your monitor. You can manipulate the gamma of your system by playing with the Xserver's idea of gamma, but the overall gamma will not be just that number. Xfree86 implements LUT manipulation through a X extension, but only allows you to set a gamma for red, green, and blue (it generates the LUT values internally). The basic commandline interface to this is xgamma, and KDE/etc have added their own versions. This is relevant to Sven's question: > > If I set a reasonable gamma value on my X server, things look > washed out and pale. Is that really desirable? If you set `xgamma -gamma 2.2` then your system will NOT have a gamma of 2.2 (unless your monitor had a gamma of 1.0, which is VERY unlikely). The "standard monitor" that is modelled by the sRGB colour space (which is meant to describe the "average" [well-adjusted] PC monitor, and is specified as the default colour space of the web) happens to have a gamma of 2.2 (as well as a white colour of 6500K and a bunch of other details). What happens in Windows and MacOS with a colour-managed system is actually in two parts. When the monitor is calibrated (e.g. with a colorimeter or photospectrometer like a ColorVision Spyder, a basICColor Squid, a Monaco Optix, etc) is twofold: First, calibration: The system is calibrated to a standard viewing condition. The brightness/contrast is adjusted to achieve reasonable black/white points, and the video card's LUTs are manipulated to achieve the target gamma/colour-temp/etc and ensure that R=G=B results in a fairly neutral colour. Note that the resulting LUT values are not defined by a simple gamma curve. At this point non-colour-managed applications (e.g. window managers) will have a consistent look across systems that have been calibrated the same way. Most people calibrate their systems to D6500 and a gamma of 2.2, primarily because this is close to the natural behaviour of most CRTs and this the LUT tables will be close to linear. Unfortunately most video cards have only 8-bit LUTs and the more "aggressive" the curve the higher the probability that you will introduce quantisation and posterisation of some colours. In fact when I calibrate the monitors on my Mac systems I specify "native" gamma where it then measures and uses the gamma of the monitor (but not all calibration software supports this). Using D6500 and gamma=2.2 also means that the calibrated system is close to sRGB. Because of its use in the web standards (and a few other reasons) sRGB has become the default colour space for non-CM files. Second, profiling: The software and colorimeter/photospectrometer measures the colour behaviour of the calibrated system and generates an ICC profile for it. This profile is stored in the system as the default profile for the display, and is used by colour-managed applications such as Photoshop to transform images from their internal colour spaces to the monitor's colour space and thus give you an accurate view of the colours represented by the image's RGB (or CMYK/etc) data. Incidentally, the calibration/profiling software typically stores the LUT data in a tag within the ICC profile. This tag is not used by Photoshop et. al. but is used by the "LUT loader" when the user logs in to reset the calibration. Unfortunately there are several vendor-specific tags being used in the Windows environment and each vendor has its own LUT loader program. On the Mac there is a standard tag, and the OS does the LUT loading. Note that because the native behaviour of monitors changes over time (and will be different if you adjust almost ANY of the monitor's controls - even physically moving the monitor can make a difference) in environments where users care about the colour accuracy of the system it's usual to recalibrate/profile the monitor on a regular basis (e.g. weekly) and only after the monitor has warmed up for 30 minutes or so. Does that description clear up anything for you? Lack of support for this stuff in the Gimp et. al. is the
Re: [Gimp-user] Re: Re: Re: Monitor for Gimp
Hi, GSR - FR <[EMAIL PROTECTED]> 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 ___ Gimp-user mailing list [EMAIL PROTECTED] http://lists.xcf.berkeley.edu/mailman/listinfo/gimp-user
Re: [Gimp-user] Re: Re: Re: Monitor for Gimp
On Wednesday 31 March 2004 03:52 pm, Jean-Luc Coulon (f5ibh) wrote: > Le 31.03.2004 22:29, John Culleton a écrit : > >On Wednesday 31 March 2004 01:34 pm, GSR - FR wrote: > >> [EMAIL PROTECTED] (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. > So how do I determine which monitors, if any can have adjustable Gamma? BTW I specified 3.0 gamma in my XF86Config file but I can spot no difference in the test files. So my current Orion monitor (17") does not seem to adjust. > -- > - Jean-Luc > > >-- > >John Culleton -- John Culleton Able Typesetters and Indexers http://wexfordpress.com ___ Gimp-user mailing list [EMAIL PROTECTED] http://lists.xcf.berkeley.edu/mailman/listinfo/gimp-user
Re : [Gimp-user] Re: Re: Re: Monitor for Gimp
Le 31.03.2004 22:29, John Culleton a écrit : On Wednesday 31 March 2004 01:34 pm, GSR - FR wrote: [EMAIL PROTECTED] (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 pgp0.pgp Description: PGP signature
Re: [Gimp-user] Re: Re: Re: Monitor for Gimp
On Wednesday 31 March 2004 01:34 pm, GSR - FR wrote: > [EMAIL PROTECTED] (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 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? -- John Culleton Able Typesetters and Indexers http://wexfordpress.com ___ Gimp-user mailing list [EMAIL PROTECTED] http://lists.xcf.berkeley.edu/mailman/listinfo/gimp-user
[Gimp-user] Re: Re: Re: Monitor for Gimp
[EMAIL PROTECTED] (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 ___ Gimp-user mailing list [EMAIL PROTECTED] http://lists.xcf.berkeley.edu/mailman/listinfo/gimp-user
