Monitor calibration and color managed workflow question

On Mon, 19 Dec 2005 10:04:53 +0100, in rec.photo.digital Stanislav Meduna wrote:

Hi,

I bought a Colorvision Spyder and calibrated my monitor. It really helped. However, I am not really sure how this works and I fear I might be double-color-managing.

The Spyder generates an ICC profile, puts it somewhere
into windows directory and registers it with the graphics card. On startup the ProfileChooser takes the default profile and loads it into graphics card. That means that I am able to see accurate colors with applications that are not
color managed – web browser, …

I thought this was the case as well, but was corrected by Bill Hilton. The colors on non-managed apps will be better, but not as good as in a color managed app.

What I do not understand is what happens when I edit the photo in Photoshop Elements (I do not have the ‘big’ PS, so I am not sure whether this is different there). If it also uses the default profile taken from windows,
I get double color-managing. And I think this is really
the case – when I open the same image in the PSE and
in the default browser, it looks that the result is not
the same – there are subtle differences in skin tones.

How is this supposed to work? Is there any way to have
both the non-managed and managed applications to display the same (i.e. let the Profile Chooser load the lookup
tables and tell the Photoshop etc. to use sRGB or whatever the display expects when the conversion is done down
in the LUT)? Or does the PSE _always_ use the default
monitor profile, whatever that is?

How do you have color management set in PSE? IIRC, by default PSE3, which I’m using a bit, sets full color management and uses the Adobe RGB color space. So you will see a difference . No double color management there. What you don’t want to do is double manage prints. Either use in the application you are printing from or the print driver, but not both. —
Ed Ruf Lifetime AMA# 344007 ()
See images taken with my CP-990/5700 & D70 at
http://edwardgruf.com/Digital_Photography/General/index.html

Ed Ruf (REPLY to E-MAIL IN SIG!) wrote:

I thought this was the case as well, but was corrected by Bill Hilton. The colors on non-managed apps will be better, but not as good as in a color managed app.

Hmm…

How do you have color management set in PSE? IIRC, by default PSE3, which I’m using a bit, sets full color management and uses the Adobe RGB color space.

Yes, that’s how I am using this.

So you will see a difference .

Ahhhh .. yes, you are right, it can well be that I compared the picture that is in the Adobe RGB space – so that’s why I saw the difference.. OK, I’ll repeat my tests with sRGB picture and PSE set to sRGB space. Then the colors should be the same in the PSE and other browsers, right?

What you don’t want to do is double manage prints. Either use in the application you are printing from or the print driver, but not both.

Yup. In fact I am trying to get the closest match possible with my printer (Epson 1800) and regardless of what I am using, I am still getting visible differences in exactly the same colors, that the spyder touches the most.

Being a technical type, I would still like to fully understand how the PSE, display profile and ProfileChooser play together in this scenario – does anyone have a pointer to some technical resources? Maybe I also try to contact Colorvision, as only they know for sure what the ProfileChooser does.

Thanks
—
Stano

"Stanislav Meduna" wrote in message

Hi,

I bought a Colorvision Spyder and calibrated my monitor. It really helped. However, I am not really sure how this works and I fear I might be double-color-managing.

The Spyder generates an ICC profile, puts it somewhere
into windows directory and registers it with the graphics card. On startup the ProfileChooser takes the default profile and loads it into graphics card. That means that I am able to see accurate colors with applications that are not
color managed – web browser, …

What I do not understand is what happens when I edit the photo in Photoshop Elements (I do not have the ‘big’ PS, so I am not sure whether this is different there). If it also uses the default profile taken from windows,
I get double color-managing. And I think this is really
the case – when I open the same image in the PSE and
in the default browser, it looks that the result is not
the same – there are subtle differences in skin tones.

How is this supposed to work? Is there any way to have
both the non-managed and managed applications to display the same (i.e. let the Profile Chooser load the lookup
tables and tell the Photoshop etc. to use sRGB or whatever the display expects when the conversion is done down
in the LUT)? Or does the PSE _always_ use the default
monitor profile, whatever that is?

Thanks
—
Stano

Hi there.

You are, like a great many other people, getting a little mixed up between your Monitor Profile and the Working Space Profile.

Your Monitor Profile, "Spyder"ed one, is only for showing the corrected colours on the screen. It adjusts the numbers from the Working Space Profile ( Adobe RGB) to correct for any inherent errors in the colours your Monitor would show.

Your Spyder software should have put the profile into the correct folder, and made it the "Default" Monitor Profile. Check this in Display Properties

Settings >Advanced > Colour Management. It should be the only profile

there, and it should be set as "Default".

Any problems with Colour, could be due to Adobe Gamma. You need to remove that from the "Start Up" Folder, because otherwise it will probably try to adjust the Monitor Colour, Double Profiling.

You also need to get a Printer Profile, to ensure that your Printer gives you the correct colours.

If your Scanner or Camera can not be set to "Tag" your images with Adobe RGB as the Working Space Profile, or can not "Tag" any Profile, then they are almost certainly working in sRGB.

The big problem with Elements is that you can not select which Profile to use as Working Space, it just seems to
use Adobe RGB.

There will always be some differences in Colour between what you see on Screen and what comes out of the Printer. In the Big PS you can use "Soft Proof" to show what it will look like using the Printer Profile for whatever Paper you plan to Print on. That is much closer, but is still not exact.

Roy G

I thought this was the case as well, but was corrected by Bill Hilton. The colors on non-managed apps will be better, but not as good as in a color managed app.

Ahhhh .. yes, you are right, it can well be that I compared the picture that is in the Adobe RGB space – so that’s why I saw the difference.. OK, I’ll repeat my tests with sRGB picture and PSE set to sRGB space. Then the colors should be the same in the PSE and other browsers, right?

No. Having a profiled monitor means that any application that uses colour management "knows" what the screen looks like. That means the application can adjust its colour output such that it can show you what your image will look like on any other device (such as a printer) provided the application also has access to an accurate profile for the other device.

Your web browser doesn’t take note of colour profiles. It will make no effort to adjust its output to match PSE or any other application. It just throws the image onto the screen. If you want to see your image the same in Photoshop and your browser, you have to tell Photoshop that’s what you want. Then Photoshop will also "throw the image onto the screen" without fussing over profiles. Under the full Photoshop you do that by selecting "Monitor RGB" as your soft-proof colour space. I’m not sure how it works under PSE.

Tesco News wrote:

Your Monitor Profile, "Spyder"ed one, is only for showing the corrected colours on the screen. It adjusts the numbers from the Working Space Profile ( Adobe RGB) to correct for any inherent errors in the colours your Monitor would show.

OK, maybe this is something that I don’t understand. My expectation is that first the working space (whatever that is, sRGB or Adobe RGB) gets converted to something independent (CIE Lab), using the Adobe RGB ICC. Then this gets converted to whatever the monitor expects using the monitor ICC. Am I right? Or does the PSE simply feed the display with whatever binary pixel values it currently has, expecting the graphics card to take care of that using the Spyder-ed data?

Your Spyder software should have put the profile into the correct folder, and made it the "Default" Monitor Profile. Check this in Display Properties

Settings >Advanced > Colour Management. It should be the only profile

there, and it should be set as "Default".

It is not the only one (I created profiles for two displays and more brightness settings), but it is the default one.

Any problems with Colour, could be due to Adobe Gamma. You need to remove that from the "Start Up" Folder, because otherwise it will probably try to adjust the Monitor Colour, Double Profiling.

Yup, did that already.

You also need to get a Printer Profile, to ensure that your Printer gives you the correct colours.

The Epson R1800 has a set of profiles and various other options – I got the best match setting the printer to ‘Adobe RGB’ with gamma 2.2 and using that as printer profile. Next best was the profile suplied by Epson, applied by the PS (with color mgmt disabled in printer driver). Something that can be downloaded from Epson as supposedly even better profile was worse. I am using original inks, original paper and printing mode that matches the profile.

If your Scanner or Camera can not be set to "Tag" your images with Adobe RGB as the Working Space Profile, or can not "Tag" any Profile, then they are almost certainly working in sRGB.

My camera allows me to choose that – I shoot with Adobe RGB + embed profile. However, at this moment I am trying to match display and printer – these things come later. The test image I tried to view and print is tagged with Adobe RGB.

The big problem with Elements is that you can not select which Profile to use as Working Space, it just seems to use Adobe RGB.

Aha. Does it matter for colors well within the gamut of both the display and printer?

There will always be some differences in Colour between what you see on Screen and what comes out of the Printer. In the Big PS you can use "Soft Proof" to show what it will look like using the Printer Profile for whatever Paper you plan to Print on. That is much closer, but is still not exact.

Interesting. What exactly does this soft proof mode do (in terms of what profile gets applied when)?

Thanks
—
Stano

Roy G writes …

The big problem with Elements is that you can not select which Profile to use as Working Space, it just seems to use Adobe RGB.

Edit – Color Settings lets you pick between ‘no color management’, ‘limited color management’ (sRGB) or ‘full color management’ (AdobeRGB). I think it actually defaults to sRGB and you have to change it to get AdobeRGB (this is with Elements 3, may be different with 4 or 2).

Also, if you open a file in a different color space like, say, Ektaspace, it recognizes the profile and lets you work in that space for that file.

Bill

Stano writes …

What exactly does this soft proof mode do (in terms
of what profile gets applied when)?

When you print a file the RGB values get translated by the software into different numbers for the printer, ideally so that what spits out on the print (‘hard proof’) looks as close as possible to what you see on the screen. This translation is a basic concept behind the ICC color managment flow, explained well here
….http://www.creativepro.com/story/feature/13605.html

What ‘soft proofing’ does is try to emulate what the final print will look like by changing the brightness and colors on the screen to mimic how the final print will appear. So you have a ‘soft proof’ on the monitor and after you apply the printer profile you can make edits for contrast and color for that particular paper/ink profile, if necessary (usually best to put these in a separate layer set).

If you have a good monitor, accurate monitor profile and accurate printer profiles then you can usually get 90-98% accuracy, but there are a lot of bad profiles floating around so for many people it doesn’t work accurately. Here’s an article explaining it in more detail … http://www.creativepro.com/story/feature/10150.html?origin=s tory

This feature was added in Photoshop 6 and Elements typically lags Photoshop in features by 2-3 versions, so maybe Adobe has included it with V 4 or perhaps in V 5 (it’s not in Elements 3).

Bill

"Bill Hilton" wrote in message

Roy G writes …

The big problem with Elements is that you can not select which Profile to use as Working Space, it just seems to use Adobe RGB.

Edit – Color Settings lets you pick between ‘no color management’, ‘limited color management’ (sRGB) or ‘full color management’ (AdobeRGB). I think it actually defaults to sRGB and you have to change it to get AdobeRGB (this is with Elements 3, may be different with 4 or 2).

Also, if you open a file in a different color space like, say, Ektaspace, it recognizes the profile and lets you work in that space for that file.

Bill

Thanks Bill.

That is what I originally suspected Elements was doing, but recently while using it on my daughters machine, all her images seemed to be Tagged with Adobe RGB. Yet, after bringing some of them home, Ps brought up the Untagged Dialogue when opening them.

I normally use Ps CS on my own machine, and gave her Elements 2 which I got free with a scanner, so I am not very expert with it.

Roy G

Roy G writes …

recently while using it (Elements 2) on my daughters machine, all her images seemed to be Tagged with Adobe RGB. Yet, after bringing some of them home, Ps brought up the
Untagged Dialogue when opening them.

In Elements 3 when you do a Save As (and probably ‘save’ as well) there’s a check box for ‘Save Options – Color: ICC Profile’ and if this is checked it seems to attach the named profile, which Photoshop then picks up. So maybe this is unchecked on your daughter’s machine or maybe Elements 2 is different than 3 on this.

I normally use Ps CS on my own machine, and gave her Elements 2 which I got free with a scanner, so I am not very expert with it.

I’m in the same boat, a Photoshop user since V 4 with several bundled copies of Elements that came with scanners and digital cameras. A friend is a newbie to digital stuff and got Elements free with his scanner so I loaded one of my copies and tried to help him learn the basics, but I’m not very good with it either 🙂

Bill

In article <do5t3g$1gfp$ says…

Hi,

I bought a Colorvision Spyder and calibrated my monitor. It really helped. However, I am not really sure how this works and I fear I might be double-color-managing.

The Spyder generates an ICC profile, puts it somewhere
into windows directory and registers it with the graphics card. On startup the ProfileChooser takes the default profile and loads it into graphics card. That means that I am able to see accurate colors with applications that are not
color managed – web browser, …

What I do not understand is what happens when I edit the photo in Photoshop Elements (I do not have the ‘big’ PS, so I am not sure whether this is different there). If it also uses the default profile taken from windows,
I get double color-managing. And I think this is really
the case – when I open the same image in the PSE and
in the default browser, it looks that the result is not
the same – there are subtle differences in skin tones.

How is this supposed to work? Is there any way to have
both the non-managed and managed applications to display the same (i.e. let the Profile Chooser load the lookup
tables and tell the Photoshop etc. to use sRGB or whatever the display expects when the conversion is done down
in the LUT)? Or does the PSE _always_ use the default
monitor profile, whatever that is?

Thanks

I’ll just paste a reply that I posted recently – this is quite a common misunderstanding and concerns the difference between calibration and a monitor profile. Sorry if it’s a bit long…

Creating a monitor profile has 2 parts:
1 – Calibration: the display is adjusted (via settings in the graphics card and maybe the monitor controls) to get things like colour temperature, gamma etc. correct. All applications see the effect of the calibration – this is what gets loaded to the graphics card when the system starts up.
2 – Profiling: the response of the calibrated display is accurately measured to create a profile of how it displays colour. This profile is used by profile-aware applications to adjust the colours sent to the graphics card and monitor. Without these adjustments, the colour displayed will not be accurate.

Photoshop or PSE, as you can imagine, is profile-aware and displays accurate colour. Most other applications (e.g. web browsers, Windows itself) are not profile-aware, do not correct the colours sent to the graphics card, and do not display accurate colour. That is why you are seeing a difference.

Unfortunately (unless your PC is a Mac!), if you want a profiled monitor you have to put up with a difference between Photoshop/PSE and most other applications. Photoshop/PSE is correct 🙂

On Mon, 19 Dec 2005 05:12:12 -0500, "Ed Ruf (REPLY to E-MAIL IN SIG!)" wrote:

On Mon, 19 Dec 2005 10:04:53 +0100, in rec.photo.digital Stanislav Meduna wrote:

….

The Spyder generates an ICC profile, puts it somewhere
into windows directory and registers it with the graphics card. On startup the ProfileChooser takes the default profile and loads it into graphics card. That means that I am able to see accurate colors with applications that are not
color managed – web browser, …

I thought this was the case as well, but was corrected by Bill Hilton. The colors on non-managed apps will be better, but not as good as in a color managed app.

Just checking… What part of the original post needs to be "corrected"?

I think it is true that a spyder app, or Adobe Gamma, or a third-party monitor adjustment app, will make a profile and register it with the OS. And that Adobe Gamma Loader, or a third-party equivalent, will set graphics card registers at startup so that the "profiled" monitor shows an sRGB image from any application (or the OS itself) correctly without any intentional color management. ("Correctly" being to the limits of whatever process created the profile in the first place, of course.)

Does a color-managed app fed an sRGB image add any accuracy to this process? It can’t be changing the graphics card registers, or you would see all the other open windows change color when it took control. So the color-managed app must be sending unmodified sRGB to the graphics card, just like a browser would.

Granted, if fed an image in any other color space, the color-managed app will provide more accurate rendering by intelligently converting it to the monitor space. Is there any other advantage?

Loren

In article ,
says…

On Mon, 19 Dec 2005 05:12:12 -0500, "Ed Ruf (REPLY to E-MAIL IN SIG!)" wrote:

Just checking… What part of the original post needs to be "corrected"?

I think it is true that a spyder app, or Adobe Gamma, or a third-party monitor adjustment app, will make a profile and register it with the OS. And that Adobe Gamma Loader, or a third-party equivalent, will set graphics card registers at startup so that the "profiled" monitor shows an sRGB image from any application (or the OS itself) correctly without any intentional color management. ("Correctly" being to the limits of whatever process created the profile in the first place, of course.)

No – only a colour management aware app will show the colours correctly. The RGB values sent to the graphics card need to be adjusted to account for the monitor profile. Adobe Gamma Loader will only load a calibration LookUp Table (LUT) to the card, but that is just a starting point for the colour management process. sRGB is irrelevant (see below).

Does a color-managed app fed an sRGB image add any accuracy to this process? It can’t be changing the graphics card registers, or you would see all the other open windows change color when it took control. So the color-managed app must be sending unmodified sRGB to the graphics card, just like a browser would.

It converts the colours from the sRGB space to the monitor profile before sending them to the graphics card. A browser does no conversion and sends the RGB values "as is"..

Granted, if fed an image in any other color space, the color-managed app will provide more accurate rendering by intelligently converting it to the monitor space. Is there any other advantage?

sRGB is just another colour space, in the same way as AdobeRGB or ProPhoto RGB. There is nothing special about it, and the same arguments apply for all working spaces.

I suggest you read my other post elsewhere in the thread – I have tried to explain how monitor profiles work and the difference between calibration and profiling.

Loren

Stanislav Meduna
The Spyder generates an ICC profile … (this) means that I am able to see accurate colors with applications that are not color managed – web browser, …

Ed Ruf wrote
I thought this was the case as well, but was corrected by Bill Hilton. The colors on non-managed apps will be better, but not as good as in a color managed app.

Loren wrote …
Just checking… What part of the original post needs to be "corrected"?

The part about "I am able to see accurate colors with applications that are not color managed". These apps don’t ‘convert’ the RGB numbers to get the most accurate colors using the icc profile, while the ICC apps that recognize monitor profiles do.

Does a color-managed app fed an sRGB image add any accuracy to this process?

Yes … as Graeme wrote, all apps benefit from the ‘calibration’ stage where you define the gamma and set a white and black point, but then the profiling software displays color patches on the screen and the puck measures them and creates a matrix file that enables programs that recognize monitor profiles to display colors more accurately.

As a theoretical example, most CRT monitors are built such that full or near full values of the RGB guns give a 9300 K white point but typically we use 5000 K or 6500 K and to get these warmer colors the blue and to a lesser extent the green guns are reduced … to make something up that I once saw on an older monitor, say 98% R, 80% G, 65% B to get 5000 K … this is for the white point, but now it’s harder to get a linear gray, meaning equal RGB values of say 64/64/64 or 150/150/150 are neutral by definition in a ‘working space’ like sRGB, but are harder to hit the more uneven the RGB gun values are (like in the example I gave). So there’s often a slight color cast in the neutrals in non-color managed apps, while this is corrected for in apps that recognize the profile.

You can turn recognition of the monitor profile on/off in Photoshop with a keystroke and if I look at a pattern like this one … members.aol.com/bhilton665/colors.jpg … and disable/enable the monitor profile what I see on my monitor is that most of the squares look the same but the saturated colors across the top shift noticeably in the reds, yellows and oranges. I came across this when web photos from Arizona and Utah’s Red Rock country looked different than even sRGB images in Photoshop as the reds dulled down. Images that weren’t first converted to sRGB looked much duller, but you still see a 2nd level effect just from the lack of monitor profile recognition.

Bill

Loren writes …
Granted, if fed an image in any other color space (other than sRGB), the color-managed app will provide more accurate
rendering by intelligently converting it to the monitor space.

Graeme writes …
sRGB is just another colour space, in the same way as AdobeRGB or ProPhoto RGB. There is nothing special about it, and the same arguments apply for all working spaces.

Actually if you view an sRGB file without the profile (like in a web browser) there’s not much change, but if you view the same file with a much wider color space in a non-color managed app then the colors can look REALLY bad … at least I think that’s what Loren is getting at.

Here’s an example of a red bird, converted to ProPhoto from the RAW (this is a very wide space, much wider than AdobeRGB) … this shows what the file looks like if I convert to sRGB and then make an untagged jpeg …
http://members.aol.com/bhilton665/card_srgb.jpg … and here’s what it looks like if I just take the ProPhoto tagged file and convert to jpeg without dumbing it down to sRGB first … all the saturated colors get dropped and it looks really really bad …
http://members.aol.com/bhilton665/card_prophoto.jpg

Granted ProPhoto is a really extreme working space but even with AdobeRGB you’ll see a lot of saturated colors fall out. I think that’s what Loren was getting at.

Bill

Graeme Cogger wrote:

Creating a monitor profile has 2 parts:
1 – Calibration: the display is adjusted (via settings in the graphics card and maybe the monitor controls) to get things like colour temperature, gamma etc. correct. All applications see the effect of the calibration – this is what gets loaded to the graphics card when the system starts up.
2 – Profiling: the response of the calibrated display is accurately measured to create a profile of how it displays colour. This profile is used by profile-aware applications to adjust the colours sent to the graphics card and monitor. Without these adjustments, the colour displayed will not be accurate.

Thanks! – that finally makes sense. So the .icc file generated by the Spyder has actually two parts:

– LUT data tht gets loaded to the card via ProfileChooser – profile that is used by the PS (and QImage and that’s
probably all on my system)

Is the LUT part also standardized somehow? I am asking because the ProfileChooser refuses to use a profile that it did not create itself – maybe because it is in some proprietary
format embedded in the vendor-specific part of the ICC?

Thanks to all that responded.

Regards
—
Stano

On 19 Dec 2005 15:28:18 -0800, "Bill Hilton"
wrote:

Stanislav Meduna
The Spyder generates an ICC profile … (this) means that I am able to see accurate colors with applications that are not color managed – web browser, …

Ed Ruf wrote
I thought this was the case as well, but was corrected by Bill Hilton. The colors on non-managed apps will be better, but not as good as in a color managed app.

Loren wrote …
Just checking… What part of the original post needs to be "corrected"?

The part about "I am able to see accurate colors with applications that are not color managed". These apps don’t ‘convert’ the RGB numbers to get the most accurate colors using the icc profile, while the ICC apps that recognize monitor profiles do.

Does a color-managed app fed an sRGB image add any accuracy to this process?

Yes … as Graeme wrote, all apps benefit from the ‘calibration’ stage where you define the gamma and set a white and black point, but then the profiling software displays color patches on the screen and the puck measures them and creates a matrix file that enables programs that recognize monitor profiles to display colors more accurately.

To further check my understanding (or confusion) here…

Am I correct that this "matrix file" is what gets loaded to the lookup table registers on the graphics card? Or is it a separate color translation containing subtle differences between what was achieved by customizing the graphics card lookup table and what the spyder saw?

Maybe I’m behind the state of the art here, but as I understand it, the graphics card lookup table translates between the three 8-bit values sent by the application for each pixel, and the three 8-bit values that get sent on to the monitor to show that pixel "correctly". If all you have to work with is eight bits, and the graphics card lookup table has already been set up optimally, what can a color managed app add to that for an image that is already in the native color space?

My thinking here is largely based on my experience with an older notebook where the backlight has gone seriously "warm", to the point where color errors are obvious. I wasn’t able to fix this with Adobe Gamma, for images inside or outside PS, and concluded Adobe Gamma had somehow stopped working. I found WiziWYG and it let me tweak the colors back to some semblance of decency. You can clearly see it load the graphics registers when its loader runs at startup, and the effect seems to be the same both inside and outside of PS (though on a notebook screen maybe the subtleties just aren’t visible).

Of course a spyder could do a much better job than I did, and optimize many more points along each color’s correction curve. But wouldn’t it load its conclusions into the graphics registers just like my manual curves get loaded? And since there are only eight bits per color to play with, how could a color managed app improve on that? (Unless the original image needs to be converted to the native color space, of course.)

I still don’t understand what happened to Adobe Gamma, though. It didn’t appear to be able to do anything to help my problem, color managed app or not. I even tried reloading fresh versions from the CD and from the web. Does it function differently from WiziWYG?

Loren

In article ,
says…

On 19 Dec 2005 15:28:18 -0800, "Bill Hilton"
wrote:

Loren wrote …
Just checking… What part of the original post needs to be "corrected"?

The part about "I am able to see accurate colors with applications that are not color managed". These apps don’t ‘convert’ the RGB numbers to get the most accurate colors using the icc profile, while the ICC apps that recognize monitor profiles do.

Does a color-managed app fed an sRGB image add any accuracy to this process?

Yes … as Graeme wrote, all apps benefit from the ‘calibration’ stage where you define the gamma and set a white and black point, but then the profiling software displays color patches on the screen and the puck measures them and creates a matrix file that enables programs that recognize monitor profiles to display colors more accurately.

To further check my understanding (or confusion) here…
Am I correct that this "matrix file" is what gets loaded to the lookup table registers on the graphics card? Or is it a separate color translation containing subtle differences between what was achieved by customizing the graphics card lookup table and what the spyder saw?

No, it’s separate. The graphics card loads 3 basic curves – one each for R, G, B. There are 2 main reasons why this is not enough:

– The graphics card knows nothing about the colour space of the original file, and therefore cannot compensate accordingly. For example, an RGB value of (200,50,20) in the AdobeRGB space is a different colour to (200,50,20) in sRGB. If you feed (200,50,20) to the graphics card, it won’t know what colour it needs to display.

– The graphics card Look-Up Table (LUT) has independent curves for R, G and B. Say you have a monitor that displays greys perfectly, but makes bright purple, e.g. (200,10,200), appear somewhat blue. The purple problem can be cured if an R value of 200 is translated to 210 and a B value of 200 is translated to 190. However, this now means that a pure grey (200,200,200) will be displayed as (210,200,190) and appear a little orange. Instead of independent RGB curves, a monitor profile uses a 3D table and can correct for these issues.

<snip>

In article <do9nrg$e23$ says…

Graeme Cogger wrote:

Creating a monitor profile has 2 parts:
1 – Calibration: the display is adjusted (via settings in the graphics card and maybe the monitor controls) to get things like colour temperature, gamma etc. correct. All applications see the effect of the calibration – this is what gets loaded to the graphics card when the system starts up.
2 – Profiling: the response of the calibrated display is accurately measured to create a profile of how it displays colour. This profile is used by profile-aware applications to adjust the colours sent to the graphics card and monitor. Without these adjustments, the colour displayed will not be accurate.

Thanks! – that finally makes sense. So the .icc file generated by the Spyder has actually two parts:

– LUT data tht gets loaded to the card via ProfileChooser – profile that is used by the PS (and QImage and that’s
probably all on my system)

That’s correct 🙂

Is the LUT part also standardized somehow? I am asking because the ProfileChooser refuses to use a profile that it did not create itself – maybe because it is in some proprietary
format embedded in the vendor-specific part of the ICC?

Unfortunately, the LUT is not standardised. The ICC file format is basically a set of named tags, and the tags used for the profile itself are well defined and standardised. There can also be optional tags for other purposes, which are ignored by colour management engines. Most profilers use a tag called ‘vcgt’ to store the LUT, but the way the data is stored within the tag is different for different apps.

Thanks to all that responded.

Regards

Loren wrote …

Am I correct that this "matrix file" is what gets loaded to the lookup table registers on the graphics card?

Graeme answered that well …

My thinking here is largely based on my experience with an older notebook where the backlight has gone seriously "warm", to the point where color errors are obvious. I wasn’t able to fix this with Adobe Gamma … I still don’t understand what happened to Adobe Gamma, though. It didn’t appear to be able to do anything to help my problem, color managed app or not.

Adobe Gamma does a very poor job with LCDs and laptops … I thought this was mentioned in the documentation. Even the original Spyder does poorly with laptops … if you’re trying to do color-critical work on a laptop you need to spend $200 or so and get the Eye-One or the Sypder 2 or the Monaco (Optix?) …

Bill

On Tue, 20 Dec 2005 22:21:25 -0000, Graeme Cogger
wrote:
….

No, it’s separate. The graphics card loads 3 basic curves – one each for R, G, B. There are 2 main reasons why this is not enough:
– The graphics card knows nothing about the colour space of the original file, and therefore cannot compensate accordingly. For example, an RGB value of (200,50,20) in the AdobeRGB space is a different colour to (200,50,20) in sRGB. If you feed (200,50,20) to the graphics card, it won’t know what colour it needs to display.

I think that part was coming clear earlier in this thread.

– The graphics card Look-Up Table (LUT) has independent curves for R, G and B. Say you have a monitor that displays greys perfectly, but makes bright purple, e.g. (200,10,200), appear somewhat blue. The purple problem can be cured if an R value of 200 is translated to 210 and a B value of 200 is translated to 190. However, this now means that a pure grey (200,200,200) will be displayed as (210,200,190) and appear a little orange. Instead of independent RGB curves, a monitor profile uses a 3D table and can correct for these issues.

Thank you! The 3D profile table as opposed to a 2D graphics card table is the part I was missing. I’d never noticed that difference in the color management descriptions I’d read. I suppose I will notice it everywhere now…

Loren

On 20 Dec 2005 15:15:48 -0800, "Bill Hilton"
wrote:

Loren wrote …

Am I correct that this "matrix file" is what gets loaded to the lookup table registers on the graphics card?

Graeme answered that well …

Indeed! I finally understand the difference.

My thinking here is largely based on my experience with an older notebook where the backlight has gone seriously "warm", to the point where color errors are obvious. I wasn’t able to fix this with Adobe Gamma … I still don’t understand what happened to Adobe Gamma, though. It didn’t appear to be able to do anything to help my problem, color managed app or not.

Adobe Gamma does a very poor job with LCDs and laptops … I thought this was mentioned in the documentation. Even the original Spyder does poorly with laptops … if you’re trying to do color-critical work on a laptop you need to spend $200 or so and get the Eye-One or the Sypder 2 or the Monaco (Optix?) …

I’ve seen that warning several places, and I’m not trying to do critical work. Just trying to avoid being grossly offended during everyday surfing… Adobe Gamma had worked well enough when the problem first began appearing, but then seemed to stop doing anything at all. WiziWYG fixed the worst of the problem satisfactorily – and could take the colors past there to wild extremes if I wanted it to.

Loren

"Graeme Cogger" wrote in message
….

Instead of independent RGB curves, a monitor profile
uses a 3D table …

This is not really the case. Monitor profiles are usually matrix based, and define three curves, one per gun, and not a 3d lookup table.

Adobe RGB, and the other popular working spaces are also matrix based, so there is generally no 3d lut in play for display of an image.

OTOH, Scanners and printers are more complex beasts, and generally do require use of the full 3d look up table for good color. —

Mike Russell
www.curvemeister.com

In article <Jvoqf.2157$>, RE-
says…

"Graeme Cogger" wrote in message
…

Instead of independent RGB curves, a monitor profile
uses a 3D table …

This is not really the case. Monitor profiles are usually matrix based, and define three curves, one per gun, and not a 3d lookup table.
Adobe RGB, and the other popular working spaces are also matrix based, so there is generally no 3d lut in play for display of an image.
OTOH, Scanners and printers are more complex beasts, and generally do require use of the full 3d look up table for good color.

Well that shows how little I know 🙂 I just checked some monitor profiles and you’re correct – they’re not based on LUTs. I’d always thought that was the norm, not the exception.

Oh well – the other point still stands, and I believe that the adaptation for the xyz co-ordinates is also not achievable via a graphics card LUT. I guess the point is that certain corrections must be made via th profile, and not the graphics card.

From: "Graeme Cogger"
….

Oh well – the other point still stands, and I believe that the adaptation for the xyz co-ordinates is also not achievable via a graphics card LUT. I guess the point is that certain corrections must be made via th profile, and not the graphics card.

Matrix profiles have RGB definitions that are in xyz.

Your main point, which is that a good monitor profile alone is not enough to produce a correct output of a tagged image on a monitor, is correct. —
Mike Russell
www.curvemeister.com