Color Management Question!

[peethasaur]

I've been reading about color management for the past couple days and I'm about a notch away from being at peace with my understanding of it. However I have some questions, and I would really love to get some education.

To start, this represents the flow of how I understand color management to work:
http://www.earthboundlight.com/image...s-pcs-flow.gif

1. Do color profiles only act as prescriptions for the display to enhance it's ability to more purely display the actual colors of sRGB or Adobe RGB, etc? In my mind, that is the only explanation that really makes sense. The idea that you could embed display profiles into images so that other displays can more accurately reproduce the original monitor's idiosyncrasies seems way messy. It would effectively create "support" for thousands of very esoteric color profiles, rather than just enhancing your display's ability to reproduce just a few true standards. However, I'm gathering from your site and others that the latter is how it's done.

2. Except, if this were true, why wouldn't you want to always use your monitor profile as your working space? That way you're always able to create all of the colors in your display's gamut, and those explanations of color will be passed on to other displays without having to mess with sRGB or Adobe RGB.

3. Also, if ICC profiles are embedded into the image, doesn't that mean your not really viewing true sRGB in the first place? Isn't a better alternative to use color spaces like sRGB to assign values to real colors; then, through your CMS, and more specifically using a PCS, your monitor could adjust it's idiosyncrasies to more accurately display the real colors of sRGB?

I have created an example that maybe you could help me understand.

4. Visit ethangodt.com/test for my example. What I've done is create a simple page with a background color set to the hexadecimal value #999999. Then, I laid out 4 images also in the color #999999, that all use sRGB as their working space, but that were exported just slightly differently. I have attached to this post 4 screen shots of the settings I used to save each image. The screenshot file names correlate to those on the site. What I'm gathering is that if you export out of photoshop using the traditional "Save as..." it will embed your display ICC profile. Similarly, if I export using "Save for web and devices..." and check "Embed ICC Profile" (which I'm not sure why that would be an option if you couldn't embed ICC profiles) the display profile will also be embedded into the image. The problem occurs when someone views theses images on the web. On my test page, the export scenarios I just gave are exemplified in images 1 & 2. I can confirm that images 1 & 2 look the same in photoshop as they do in my browser, but do not match the background of the page. Remember, those images were created using the working space sRGB, but also have the embedded ICC profile. With images 3 & 4 I saved using "Save for web and devices..." but unchecked "Embed ICC profile" in both examples. Those images do not match the color that I see in photoshop but appear to match the CSS background of my site.

Maybe you can explain to me what's going on? I would really appreciate it... like... a lot...

Also, be aware that the attached images are not in the correct order. Go by file name.

Thanks for your time!

[Colin Southern]

Hello Peethasaur,

I only have a few minutes, but in summary ...

1. Think of profiles as translation tables that convert something from "what it is" to "what it should be". They're not only for monitors - they're also used to standardise the performance of cameras / printers / scanners etc.

2. You wouldn't enbed a display profile because that wouldn't make any sense - you may embed a profile that tells other devices how to standardise the collection of data that they're dealing with. For example, telling your PP software that the data represents sRGB or Adobe RGB - rather than just a collection of what we call "mystery meat".

3. You don't want to use a monitor profile as your working space; your monitor profile adjusts the data SENT TO THE DISPLAY so that it displays correctly on the screen - it doesn't affect the working data, wereas using a monitor profile for a working space would give you a double-conversion and probably bad results.

4. With regards to #4, it really depends on the colour space you're using. If you use a device-independent space like LAB then that's an absolute colour reference in it's own right, but spaces like sRGB and Adobe RGB aren't - so they need something to be referenced to - and that's a source profile.

If you REALLY want to get to grips with all of this then there's one reference text that stands head and shoulders above all the rest - it's Real World Color Management 2nd edition, by Fraser, Murphy, and Bunting - and it's available from Amazon.com in both printed and kindle formats (I'd strongly recomment getting the kidle edition and then viewing it on your PC - you can be reading it 10 min from now )

Hope this helps - sorry it's so rushed.

[Polar01]

I am going to add something about ICC profiles, each and every paper will produce a different result, same printer, same photo. If you were to load 10 different papers into the same printer and print the same shot, none would be the same. The ICC profile will tell the system how to change the output of the printer and with the ICC specs of the paper, each photo printed will appear as you saw in on screen.

[Colin Southern]

I am going to add something about ICC profiles, each and every paper will produce a different result, same printer, same photo. If you were to load 10 different papers into the same printer and print the same shot, none would be the same. The ICC profile will tell the system how to change the output of the printer and with the ICC specs of the paper, each photo printed will appear as you saw in on screen.

There's quite a few variables when printing ... paper is one, inkset is another (generally consistent for a given manufacturer, but different gamuts when changing from (for example) Epson to Lyson), the printer itself, and media setting used when printing (eg if you tell the printer it's 280gsm paper when it's only 180gsm - and you profiled for 180gsm you'll get different results even if you use the right paper). Then of course the reflectivity changes depending if the likes of canvas has been sprayed or not ... fun fun fun

[peethasaur]

Thanks a ton you two - I really appreciate it.

I'm pretty sure you've confirmed my understanding. I do still have some cloudy areas, though.

1. In Photoshop, when you choose to save using the "save for web and devices..." function, why is there a check box for "Embed ICC Profile" and "Convert to sRGB"? Isn't sRGB a color profile? So if I unchecked "embed..." but check "Convert to sRGB" wouldn't I still be embedding a color profile?

2. I know that it can be difficult to troubleshoot since you are not with me, but is there anyway you could explain why I'm seeing the results that I am in the "What I See" image that I have attached? I'm confused because it is only happening when I choose to embed the ICC profile... I'm further confused because when I view the test page on my iMac (my other computer) or any other display, all of the images I have on the page match the background-color.

Thanks again for your time. I'll definitely be checking out the book you suggested.

-ethan

[Colin Southern]

Hi Ethen,

sRGB is a colourspace - basically it's an attempt to standardise colour around the least-common-denominator gamuts of most monitors. These days it's a little dated, but it's still the best one we have. Many have sung the praises of colour managed browsers, but in reality, they don't accomplish a lot (I wrote a bit about it here).

Best advice I can give is "don't check out the book - just buy it". After 2 or 3 reads and a few painkillers for the headaches, you'll go from being the one asking the questions to the one answering them for us

[peethasaur]

Thanks again Collin. There seems to be some ambiguity on the web over coining sRGB or Adobe RGB as a profile. I apparently got confused... Thanks for the education.

-Ethan

[Colin Southern]

Thanks again Collin. There seems to be some ambiguity on the web over coining sRGB or Adobe RGB as a profile. I apparently got confused... Thanks for the education.

-Ethan

There are many who think that they're better off posting their images to the web using Adobe RGB because of the greater gamut, but they seem to forget that many are still limited to sRGB devices (putting a 300MPH speedo in your car ain't gunna make it go any faster!), and the majority of browsers aren't colour managed yet anyway. I think the gamut of monitors is steadily improving (with many reporting close to Adobe RGB), but in my opinion, it's just not worthwhile until the vast majority have Adobe RGB capable monitors - are using colour-managed browsers - and are using calibrated and profiled monitors (long long way off).

So in the real world, my suggestion is to stick with sRGB for online display and for printing from low-end print shops - and use Adobe RGB if you're printing yourself or using high-end shops (Adobe RGB has a gamut that better encapsulates what printers are capable of).

Unfortunately, we live in a far from perfect world

[herbert]

Hi Ethan,

In the real world there are a set of colours that we can see. In the computer world there are many ways to represent this set or a subset of those colours. What colour management does is tell your computer how to convert one representation to another so the colour looks the same.

The monitor profile is important to your computer. It tells your computer how to show the images you have on your system. However someone else with a different monitor will need a different profile to show the same image because their monitor works differently. With good profiles the two monitors should look the same when side by side (as long as they can both display the actual colours in the image).

It is better to use a standard profile when editing and passing around images. This is because if the profile is not embedded or it is ignored then the application can make a safe assumption about what profile it is. In the case of web images this is sRGB.

The second reason is that standard editing profiles are grey balanced with a smooth tone curve. This means that the same amount of R, G and B on a pixel represents grey. It also means that an adjustment of a standard amount, e.g. +5, will have the same perceived change on the image whether the start value was 10, 50 or 100.

Monitor profiles do not respond this way because they represent how your monitor differs from a nice smooth colour response. So if you used it as your working space when you edited saturation and exposure in photoshop the image colours would slide out of whack.

Regards,

Alex

[Colin Southern]

Well put Alex - I wish I was thinking that clearly at the moment!

[Macmahon]

Ethan
Colin is right. The Bible on this stuff is the late Bruce Fraser's book. But it's not for the faint hearted, and it sure ain't bed time reading.
I tried to make an easy introduction to the roles of ICC profiles and the roles and differences between colour spaces in a few web pages: check out "About Colour Management" in www.fromcameratoprint.com
Might make RWCM easier to digest when you get to it!
Cheers
Tim

[herbert]

Well put Alex - I wish I was thinking that clearly at the moment!

I had a good night's sleep.

I think this is often made more complicated than it actually is. ICC colour management is like a big set of translation dictionaries. We use it so we all know the meaning of the words in the language we are most familiar with.

Alex

[peethasaur]

Thanks again. I just got around to reading your most recent responses. I'm buying that book! Your teaser about "smooth tone curves" makes me want to dive straight into this stuff. Really, I'm not so much a photographer as I am a graphic designer and motion graphic artist. However, the knowledge required in each overlaps, and luckily for me, you guys can steer me in the right direction.

One more question though ( to preface: I really will be getting that book, and after I finish it I'm sure this concept will be very clear. For now, please avoid the desire to put your face into you palms and mutter, "this guy just isn't getting it..." ): Could you tell me what exactly I am embedding if I click to "embed ICC profile" via Photoshop's "Save for Web" method? I must be getting confused by terminology because if it's not something like sRGB, and if it's not a dsiplay profile, I'm not sure what I'm actually embedding.

You guys rock. Thanks again, and merry Christmas!

-Ethan

[herbert]

Hi Ethan,

The thing you are embedding is a set of information that says how to convert your image to/from a profile connection space (usually CIE XYZ or CIE L*a*b). This information is written in a standard format defined by the ICC as an ICC colour profile. Any colour space aware application can read this and know how to convert your image to the profile connection space. The image can then converted to any other space you desire, e.g. monitor, printer, CMYK, Adobe RGB, sRGB, etc.

It is very neat when it works. When it doesn't it causes everything to look like a 3 year old has played with your photoshop sliders. This is why you should go the safe route and use sRGB when producing images for the world. It is the one space that should look ok to everyone, colour managed or not.

When you click save for web your image is converted to sRGB and the sRGB profile is added to file. So colour managed applications know what it is and non-colour managed applications that assume sRGB will also be OK.

The sRGB profile is small so it will not effect the image size very much. It is best to leave it there unless you have a strong need not to.

Alex

[Simon Garrett]

Just to add to the various comments above about device profiles, colour spaces and sRGB (or Adobe RGB).

A profile describes the characteristics of a physical device, including a description of its colour space (the range of colours it can display), definition of white point and a tone curve (e.g. a gamma curve). sRGB and Adobe RGB are standard profiles and you can think of them as profiles for virtual devices. Images are usually stored either in original raw form (in the colour space of the camera sensor) or converted to a standard colour space such as sRGB or Adobe RGB.

Then (in a colour-managed workflow) they are converted again to the monitor's colour space, using the monitor's profile. Or converted to the printer colour space using the printer profile (usually one profile for each type of paper for the printer).

Images often have an profile embedded as an easy way of saying what colour space the image is in. The embedded profile tells you what device the image will display correctly on (without further conversion). The profile doesn't have to be embedded, but lots of software assumes jpegs and tifs are sRGB unless they contain an embedded profile for something else, so best to embed the profile if it isn't sRGB (and to be on the safe side, even if it is - some software doesn't assume sRGB).