Help Explanation Calibration/Color Spaces/Profile - Convert To

[TomasDN]

Hi,

I'm trying to figure out the flaw in my logic when thinking about color spaces and conversions between them. If you could follow along with me, and correct me when needed, that would be very helpful.

I'm just going to focus on non-print situations at the moment, for that is what I am mostly confronted with. I'm going to pour the things I've been thinking about for quite some time, so I apologize in advance for the length of this text:) and I would also like to thank you in advance.

Here's where I am at at the moment:

A digital image its colors are made up out of values which represent three channels: Red, Green and Blue (RGB). These values are just numbers (let's assume we have an 8 bit image, so 256 values) and the software program with which you open an image tells the monitor what numbers are in the photo and what color profile is incapsulated in the photo (so how the monitor should show that color).

Question 1: When I am looking at an image on a monitor in a software-program, like Windows Photo Viewer (or any other simple software program for that matter), and there is no color profile attached to the image, how does my monitor show the colors? Does all software have some sort of default-color space with which it interprets colors? Or does some software have no default-color space and is the numerical information simply transferred to the monitor to interpret according to its factory settings?

If I open a photo in Photoshop that has no color space encapsulated, the interpretation of this photo will be done according to Photoshop's working space (you need to choose a working color space, because otherwise Photoshop can't do anything with your photo. It wouldn't be able to do anything the numbers which are the photo in essence).

Question 2: Here my knowledge falls a bit short because of practical experience with calibration. I have an Imac at home, and there are a lot of color profiles to choose from in the Preferences-window. There is the standard color profile which I assume is the profile which tells my monitor that, for example 255, 0, 0 is the most saturated red it can produce. In other words, this is the profile that uses all the color capabilities of my Imac. Then there are the device independent ICC-color spaces such as sRGB, Adobe RGB,... I assume that when I bought this computer, Apple made sure that these profiles would counter the abnormalities in my monitor. What I mean is, they actually calibrated my computer for me and made profiles of all these calibrations for the different color spaces?

I understand that my monitor could have shifted in the passing of years, so perhaps I need to calibrate my monitor again. What I do not understand is how the color settings in Photoshop work with the color profiles in the Preferences window? When I work in sRGB in Photoshop, does Photoshop actually tell my OS to use its sRGB-color profile to show the photo on the monitor?

And if I see in the Photoshop color settings that I can choose to emulate a Fuji-filmstock, how does Photoshop communicate with my OS to make sure that what I see is correct? There is no Color Profile in my preferences-settings of my Imac for Fuji-filmstock.

To conclude a question about Photoshop's Profile- vs. Convert To-settings: When I open an image with no color profile incapsulated, the photo is shown in Adobe RGB because that is the working color space in my case. Nothing happened to the actual numerical values of the image. The numbers are just interpreted and show the color as if these numbers were always meant to be Adobe RGB. This is also what happens when you Profile  a photo.

If you convert a photo in Photoshop, say from Adobe RGB to sRGB, the numerical values will change in an attempt to stay visually as close to the original as possible.

However, when I convert an image without color management but viewed with an Adobe RGB-profile, to Adobe RGB, the colors change drastically. I don't understand why that happens. I mean, the numerical values should stay the same, right? So the colors should stay the same as well, since I was viewing the photo in the same color space as I now want to convert it, no? Photoshop could not possibly know how the original image was intended to look because there was no color space encapsulated? So what is Photoshop's logic in this case? Just in case you're wondering, this is a question to better understand how Photoshop thinks. I don't think this is actually a useful action to do, right?

If some questions aren't clear, please let me know. I'm quite anxious to finally get an answer to these questions, so I'll be more than glad to make it all clearer.

Thanks,

Tomas

[D Fosse · Accepted solution]

RGB values are relative to the color space they refer to. Any given set of RGB values will produce different actual colors in different color spaces.

A color space conversion always needs two profiles: the source profile, and a destination profile. These two profiles are used to remap the RGB values from one to the other. With this remapping, the numbers are recalculated and changed so that color appearance is preserved. Otherwise the perceived color would change in the new color space.

A profile is a detailed description of a color space. Your monitor profile is a description of your monitor's actual and current behavior - its native color space at the current state.

A color managed display path uses the document and monitor profiles to remap, recalculate, the original RGB values accordingly. These recalculated RGB values are sent to the monitor. This way the file is correctly represented on screen.

Without color management, the RGB values are not corrected, but just sent straight through unchanged. Many applications will do that if the file has no embedded profile. There's nothing to convert from, and so the operation is undefined.

Other applications, including Photoshop, will assign a default profile if none is present. This is the working space. This allows the normal color management chain to operate.

[D Fosse]

BTW you shouldn't put too much trust in "factory calibration". That's just a marketing gimmick. A calibrator is a must if you take color seriously.

[Conrad C]

TomasDN  wrote

Question 1: When I am looking at an image on a monitor in a software-program, like Windows Photo Viewer (or any other simple software program for that matter), and there is no color profile attached to the image, how does my monitor show the colors? Does all software have some sort of default-color space with which it interprets colors?

Recent operating systems generally assume sRGB for images without embedded profiles. That usually works fine as long as the image actually is sRGB, but obviously if the image uses another color space it's probably going to look wrong in non-color-managed software.

TomasDN  wrote

Then there are the device independent ICC-color spaces such as sRGB, Adobe RGB,... I assume that when I bought this computer, Apple made sure that these profiles would counter the abnormalities in my monitor. What I mean is, they actually calibrated my computer for me and made profiles of all these calibrations for the different color spaces?

No, the device-independent profiles like sRGB etc. were not adapted to your display at all by Apple. They are included as is for compatibility so that, for example, the sRGB or Adobe RGB profile is present for use by any application on your Mac. They should not be applied to your monitor in Displays Preferences. A display profile should only represent the exact characteristics of your monitor. If you choose ProPhoto RGB in Displays Preferences, that does not make your display behave as a ProPhoto RGB monitor. It tells the system that your display is ProPhoto RGB, which is wrong because the hardware is technically incapable of covering all those colors. (There are no ProPhoto displays.)

Those device-independent profiles are there for use with files, not displays. You will see this if you select the option "Show profiles for this display only." Now the list will probably show the one factory profile Apple did make for your display, which is probably "iMac" or "Color LCD." There may be more profiles listed if you ran your own display calibrator/profiler.

It's only a good idea to apply sRGB or Adobe RGB as a display profile when you have used calibration hardware that can verify that it's exactly achieving sRGB or Adobe RGB when no other profiles are involved. But the way this is done is technically not possible with an iMac; it's a feature of some advanced non-Apple external displays. So an iMac must use a custom display profile that is not sRGB or Adobe RGB.

TomasDN  wrote

What I do not understand is how the color settings in Photoshop work with the color profiles in the Preferences window? When I work in sRGB in Photoshop, does Photoshop actually tell my OS to use its sRGB-color profile to show the photo on the monitor?

All Photoshop does is hand off the image to the system for display. Photoshop might tell the Mac, "Here's the image, it's in sRGB." The Mac system says "OK thanks, I will convert it from sRGB to the iMac display profile." If the display profile is up to date, the iMac display will show the colors as closely as it can.

TomasDN  wrote

And if I see in the Photoshop color settings that I can choose to emulate a Fuji-filmstock, how does Photoshop communicate with my OS to make sure that what I see is correct? There is no Color Profile in my preferences-settings of my Imac for Fuji-filmstock.

The reason the Fuji film stocks aren't listed in Displays Preferences is that they are not ICC color profiles! They are color lookup tables (color LUTs). They are not really for photography although they can be used for that. They are primarily intended for color-grading video clips, mostly used in Adobe Premiere Pro and After Effects but can be used in Photoshop to make image colors consistent with the video projects they will be used in. I think all the film stocks listed are motion picture film, not still camera film.

If you applied a Fuji LUT to an image, the same rules apply. You would not apply it in Displays preferences, there is no need because again, if you are to see the colors correctly it must be converted from the document color space (Fuji) to the display color space (iMac display profile), and that happens automatically.

Another reason the Fuji LUTs aren't listed in Display Preferences is that, since they aren't ICC profiles, they are not in the standard folder locations where the Mac system looks for profiles. If you want to know where all the ICC profiles are found, open Apple ColorSync Utility on your iMac and click Profiles. The Fuji LUTs are not in any of the profile folders. Where are they? You can find the Fuji LUTs and others at:

/Applications/Adobe Photoshop CC 2017/Presets/3DLUTs/

[TomasDN]

Sorry for the somewhat delayed response. I needed some time to process the information you gave me. Thanks for answering my questions like you did. That was already very helpful!

If anyone is interested in getting a basic understanding of this subject, I found a very helpful site which made me understand a bit better what is happening: http://www.color-management-guide.com/icc-profiles.html#resume

I’ve also found another post where somenone is asking the same questions as me, and overcomplicating things, as Mr. D Fosse says:) He also answers my questions quite good there: https://forums.adobe.com/thread/2119166

However, I still don't understand a few things. It's going to take a few more posts before I'ùm completely following, I guess. Again, correct me if I’m wrong, please…

The Imac-color profile is the profile that is there to ensure that:

• I'm utilizing the fullest possible range of colors I can achieve with that display whenerver I’m not in color-managed environment, for example when I’m looking at pictures in a very basic software programs. Or when I’m looking at my desktop I am looking at the colors of the Imac-color space.
• As a reference point to recalculate from when I'm viewing images in Adobe RGB, sRGB,... in a color-managed application.

So does that mean that when I view an image in Photoshop in, for example Adobe RGB, Photoshop tells the computer to recalculate from it's Imac-color profile to a correct Adobe RGB-color space? That is, if we assume just for simplicity that the Imac-color profile setting is actually accurately calibrated. Then I’m looking in Photoshop in a certain color space but everything else that’s happening on my computer is still shown to me in the Imac-profile colors?

If that is correct, I’m just wondering about non-color managed images in Photoshop. Are these shown to me in the full gamut of the monitor, as is defined by Imac-profile? From what I understand now, when I calibrate a monitor, the calibration software first checks what kind of wavelenghts the monitor is able to output, then it goes to see in what way the output of the monitor deviates from the colors it expects to see in a very large color space like CIE LAB when certain values are sent to it (with values I mean RGB-values like 255, 255, 255).

But what does it do then? It can’t show a full CIE LAB-color space, so does the software then just say: ok, I have all the information I need to properly convert from these LAB –values of the monitor to any color space. I’m going to remember those, but as for now, I’m just going to show the fullest possible color space I can with this monitor. By that I mean: for RGB-value 255,0,0 it is going to show the most red color the monitor can show, for 0,255,0 it is going to show the most green color it can show,… Is that what’s happening?

[TomasDN]

Oops, forgot part of my post. Beneath is the rest of it:

Another thing I don’t get: Why are there Adobe RGB, sRGB, …-profiles in the Display Preferences when no screen is exactly equal to one of these color spaces? Why would you ever use these settings? Is it because some monitors are possibly closer to the sRGB-color space than to the Imac-color space, and when you don’t have the means to calibrate you can still get fairly close with those profiles?

You said it's for reference for Photoshop, but Photoshop doesn't need the profiles to be in the display preference window, right?

I’m also still having a problem with following the reasoning of Photoshop below. If anyone could shed a light on that, that would be very helpful :

To conclude a question about Photoshop's Profile- vs. Convert To-settings: When I open an image with no color profile incapsulated, the photo is shown in Adobe RGB because that is the working color space in my case. Nothing happened to the actual numerical values of the image. The numbers are just interpreted and show the color as if these numbers were always meant to be Adobe RGB. This is also what happens when you Profile  a photo.

If you convert a photo in Photoshop, say from Adobe RGB to sRGB, the numerical values will change in an attempt to stay visually as close to the original as possible.

However, when I convert an image without color management but viewed with an Adobe RGB-profile, to Adobe RGB, the colors change drastically. I don't understand why that happens. I mean, the numerical values should stay the same, right? So the colors should stay the same as well, since I was viewing the photo in the same color space as I now want to convert it, no? Photoshop could not possibly know how the original image was intended to look because there was no color space encapsulated? So what is Photoshop's logic in this case? Just in case you're wondering, this is a question to better understand how Photoshop thinks. I don't think this is actually a useful action to do, right?

Thanks for the input !

[D Fosse]

Yes, you really are overcomplicating.

An icc profile is a description of a color space. That's all it is, and that's all it needs to be. But the description has to be accurate for this to work. That's why you can't just "try" different profiles. Only one is valid - the right one.

With that established, here's what happens when Photoshop displays an image: Using the document profile and your monitor profile, the RGB values are remapped/recalculated from the document color space into the monitor color space.

So you have a standard profile conversion from, say, Adobe RGB, to your monitor profile. These converted/recalculated values are sent to the monitor, now remapped to reproduce accurately on this particular monitor.

For best accuracy this monitor profile should be made with a calibrator. The generic profiles that come with the OS are just ballpark. For many people that's good enough.

[abharat_in]

Hi TomasDN,

Following are some inputs regarding "Assign Profile" & "convert to Profile" options in Photoshop:

A] Use-cases for "Assign Profile" option

01. When you open a non-profiled image (image that does not have any embedded/assigned color profile) - image renders using the working space profile.

02. When you open a profiled image (image having an embedded/assigned color profile) - image renders using the profile available with the image (provided that color management policy under color settings is set to preserve embedded color profiles)

*Note - In both the cases mentioned above, there is no change in color numbers of the image colors and colors only simulate based on available color profile. In the process of this simulation, image colors are first converted from image numbers to an independent color space using the mapping defined for input data of source color profile (either of embedded or of working space); and then from independent color space, colors are further converted to RGB color space using the mapping defined for output data of destination color profile, which in this case is always the color profile set for monitor display preferences at OS level. Please do remember that this color conversion is only for simulating colors on monitor & thus are not persistent. Which also means that there is no actual change in image color numbers as already mentioned above.

So we can say that in all color managed apps like Photoshop, the value of colors being shown in app (like shown in 'info' pane of Photoshop as per default settings), does not directly represent the colors being displayed on monitor. Which leads us to the importance of monitors being properly calibrated as per our workflow needs so that we get the rendering of image colors as close to the destination (or our requirement) as possible. This statement does not mean that a non-color managed app will render colors properly but on the contrary, level of in-accuracy is more in such apps.

B] Use-cases for "Convert To Profile" option

01. When convert-to-profile option is used for a non-profiled image - color numbers are converted using working space profile as source & profile selected in 'convert to profile' dialog as destination.

02. When convert-to-profile option is used for a profiled image - color numbers are converted using embedded/assigned profile as source & profile selected in 'convert to profile' dialog as destination.

*Note - In both the cases mentioned above, the color value or color numbers get changed using source & destination color profile. In this conversion process, image colors are first converted to an independent color space using the mapping defined for input data of source color profile; which is then converted to the destination color profile using the mapping defined for output data of destination color profile, which in this case is the color profile selected in 'convert to profile' dialog. Thus color conversion is persistent here which can be clearly verified using the 'Info' pane in Photoshop.

In addition to this conversion, Photoshop further assigns the selected destination color profile to the image (without alerting the user but as an inherent step); which means that the color numbers finally available in image after color conversion are being simulated to render on screen using the destination color profile and not the color profile set as working color space. If you want to render your converted image colors using the color profile of your working space then you will have to first un-assign the profile.

Hope this might help to some extent.

Regards,

Ajay

[TomasDN]

Thanks everyone!

I think I'm starting to get it somewhat. I still need to finesse some things in my mind:) but I'm starting to understand how Photoshop deals with colors. I'll certainly be back with some more questions sooner or later, but for now I'm quite fulfilled.

Thanks again,

Tomas