Hi Peter, Well, you could do that, but I'm not sure this is really what you want.
For a "true" match to screen you would need a D50 box. Then, you could place the print under the D50 illuminant, and yes, in such situation the monitor would show you colors the print should have. But please note this often involves a hard yellow cast. More normal usage would be to use perceptual or relative colorimetric to check the *appearance* of image, that is, how an observer adapted to media, whatever this means light, paper or a combination of both, does perceives the image. Absolute colorimetric match to screen means colors does match UNDER D50, but tells nothing about the personality of the print under any other illuminant. For that reason IMHO is best to use perceptual whatever possible, and leave absolute for very special cases. To check whatever printer is using correct workflow, for example. Regards, Marti. ----- Original Message ----- From: "Peter Gregson" <[EMAIL PROTECTED]> To: "Marti Maria" <[EMAIL PROTECTED]> Sent: Friday, January 30, 2004 7:58 PM Subject: Re: [Lcms-user] Re: Re: LittleCMS (interpolation) Marti, In your answer, you say that Absolute is rarely used, onlyfor match to screen or proofing. I am doing digital photography in which I want to proof my prints on the monitor. Should I be using Absolute intent? Regards, Peter On Friday 30 January 2004 11:24, Marti Maria wrote: > Hi, > > I'm taking the freedom to forward the response to lcms mailing list. > Forgive me if any inconvenience, but I think this could be of interest > to other users too. > > >ISSUE: > >---------- > > I create 2 profile for my monitor using Adode Gamma > > software. Both the profile are created in exactly similar > > method, except that is chose different "Color Temperature" > > for each of them. Now i use LittleCMS to convert a RGB value > > to another RGB valued using the profiles a "Source" and > > "Destination" profiles, and using Absolute colorimetric as the > > indent.. i.e i am just trying to scale the image from one Color > > Temperature to another. > > > > If i give same R, G, B values (i.e a grayscale image) the output > > is an R, G, B values which now are not same (neither close by). > >So in this case an image which is a Grayscale will become a Colored > >image. > > > > Ex: 255 , 255, 255 as input will give me 255, 252,189 as output. > > Is this correct ?? > > > > If i used any other intent, the output is similar to the input. > > > > I have observed this in ICM also. > > Welcome to the wonderful world of color! ;-) > > This is not a bug, nor a problem. Is the correct behavior. > I will try to do a quick explanation by an example. > > For this experiment you would need two monitors, which you > should be able to set hardware white point (temperature). > > Place both monitors side by side. Set first to D50 (5000K), and > second to D93 (9300K). Do it adjusting monitor controls. NOT > by using any software. > > Then, using your favorite paint program, draw a white rectangle > with value (255, 255, 255) on both screens. > > Take a look. The D93 monitor will show the white patch as "bluish" > whilst the D50 will be quite yellow. > > This effect is not noticeable unless you place both monitors together. > It happens that eyes got used to monitor and somehow "discounts" these > blue/yellow cast. This is know as "chromatic adaptation", and is a > important part of human vision. > > So, if you were using a color management system, you could transform > this white to look same in both monitors, no matter which hardware white > point they are using. And certainly a CMM can do that, this is the > goal of absolute colorimetric intent. So, in the D50 monitor, the CMM > would add some blue to compensate the yellow, and in the D93 monitor > some yellow to compensate the blue. > > In the other hand, most times you don't need this "match to screen" > feature. Your eyes are used to the hardware white point, and want > gray to be neutral with respect to monitor. This is how works rest of > intents: perceptual, relative colorimetric and saturation. Absolute > colorimetric is rarely used, only to do match to screen or proofing. > > Hope this helps, > Marti Maria > The little cms project > http://www.littlecms.com > [EMAIL PROTECTED] > > > > ------------------------------------------------------- > The SF.Net email is sponsored by EclipseCon 2004 > Premiere Conference on Open Tools Development and Integration > See the breadth of Eclipse activity. February 3-5 in Anaheim, CA. > http://www.eclipsecon.org/osdn > _______________________________________________ > Lcms-user mailing list > [EMAIL PROTECTED] > https://lists.sourceforge.net/lists/listinfo/lcms-user -- Peter H. Gregson, Ph.D., P.Eng. NSERC Chair in Design Innovation Director, iDLab Professor tel: (902) 494-2175 fax: (902) 494-2096 e-mail: [EMAIL PROTECTED] web: www.iDLab.dal.ca ------------------------------------------------------- The SF.Net email is sponsored by EclipseCon 2004 Premiere Conference on Open Tools Development and Integration See the breadth of Eclipse activity. February 3-5 in Anaheim, CA. http://www.eclipsecon.org/osdn _______________________________________________ Lcms-user mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/lcms-user
