Assign Profile vs Converting to Profile

[Printer_Rick]

This relates to a very lengthy thread in the InDesign forum, "RGB vs CMYK images and resolution"

I have a lot of questions (perhaps confusing) relating to RGB color gamuts. To simplify let's start with 2 gamuts, ProPhoto and Adobe RGB

I have a profile editor that can view both of these within potato-shaped Lab gamut. They are of course both triangles, I believe all RGB gamuts are. I can see ProPhoto is considerably larger than Adobe RGB, containing more fringe colors

I also see that the gamma of Adobe RGB is 2.2. The white point is 6500K

The gamma of ProPhoto is 1.8. The white point is 5000K

I understand gamma to be "black point". Or better yet "black density". On a press sheet, ink density can be measured with a densitometer. In my experience a density reading of 2.2 on a press sheet would be very dark. Is my understanding correct - that gamma (RGB) is comparable to ink density (CMYK)? Perhaps better to state as an analogy: Gamma: RGB as Density: CMYK

My monitor RGB profile has a gamma of 1.8 (mac standard). This tells me that the Adobe RGB gamma of 2.2 has to be re-interpreted on my display. Is that correct?

As for white point, that would be the RGB equivalent of CMYK paper white.

The InDesign forum has a lot of discussion about assigning profiles, vs converting to profiles. My understanding is that assigning a different RGB is actually a "pure" conversion. The pixels are left completely intact. There is no move to Lab, and back to RGB. It's taking the image and effectively dropping it into a brand new gamut, The price for this, of course, is that the appearances of the colors are completely redefined, and this appearance shift can at times be radical.

For example, if I have an ProPhoto image open, then assign Adobe RGB, I can see very clearly that the image becomes darker on-screen, and the color "shrinks"

As a prepress person, I have often used re-assigning in RGB mode as a very effective color correction tool. Usually it's turd polishing, to be quite honest, when critical color match is not an issue. The scenario is usually a crappy sRGB image. I assign Adobe RGB, which as the Adobe description states is ideal for conversion to CMYK. I must add that I always use proof preview, I am well aware that Adobe RGB has colors far beyond a standard CMYK gamut. But when I convert to CMYK, using Adobe RGB as the source, the image color is expanded, and the result on press is often vastly improved.

I will also add that as a prepress person, I don't go re-assigning in this fashion without the customer's consent.

In the InDesign forum, this "re-assigning" has been referred to as "random color". There is a lot of emphasis on color appearance, and maintaining color appearance. The consensus therefore is that if you had an sRGB image, you should convert to Adobe RGB. But then it is my understanding that you miss out on the often huge benefit of gamut expansion. If you wanted to expand color after converting, you have to do color corrections, which alters the pixel data and in the strictest sense is destructive (unless you use adjustment layers).

All this leaves me wondering - if assigning is such a no-no, why is it available? Probably the main reason for the assign capability is to assign profiles to images that don't have an embedded profile. Sometimes users unknowingly discard profiles, if the color settings policy is set to off. When another user open the image, he quickly sees the image does not have a profile.

Normally he would assign his working space, since that is affecting his visual on-screen appearance. But he can't know for sure if that's true to the original capture.

Which brings up another point. Any device doing the capture (camera or scanner) has a gamut. This gamut is an input profile.  When the image is translated from device capture into digital file, should this input profile be embedded in the image?

At this point I'm not sure about this. I have a 7.1 MP camera, and the downloads always have sRGB embedded. Not a profile specific to the Kodak model. My guess is that sRGB is a universal standard, representing the gamuts of monitors and desktop scanners. It is the working space of the world wide web. So it's more or less the default RGB, and is also the default working space in all Adobe applications (North America general purpose).

But the description of sRGB is very clear. It is not ideal for prepress, this is stated in Adobe's description. It is small. This may make it comparable to CMYK, but it is still not ideal for conversion to CMYK. And in fact there are CMYK colors that fall outside of sRGB. Especially if you are dealing with the larger CMYK gamuts corresponding to new offset screening technologies (FM screening and concentric screening)

So why in the world would someone convert from sRGB, to Adobe RGB? There's no benefit at all. May as well leave it sRGB, instead of converting. And the even bigger question - how do you know that sRGB is "true" color? To me, the true color is the original subject. In the case of a photo, that might be just a memory. In the case of a scan. it's the original, but the user might not even have that, if someone else did the scan and all he has is the digital file. So who's to say that the embedded profile - sRGB - is a fair representation of the original?

Re-assigning RGB profiles may be an odd way of adjusting color. But it can be effective. Why would the assign option be readily available, if not to translate colors to a different gamut, without altering pixel data? Seems to me it is the primary reason Adobe developed the assign option in the first place.

I know this is a lot of questions. Any input on any of these matters would be greatly appreciated.

[Ramón_G_Castañeda]

Try again, posting only one question per post, as concisely as you can.

[Ramón_G_Castañeda]

I don't think your post is going to find many users here willing to read it in its entirety, and even less who will attempt to answer it.

You make an awful lot of wrong assumptions, a lot of irrelevant ones, and many unnecessary ones.

Start learning about Color Mangaement here:

http://www.gballard.net/psd/cmstheory.html

In the next post, I'll explain the difference betwen Assigning and Converting to you.

[Printer_Rick]

Ramon,

Sorry for the lengthy initial post. I appreciate your response. I know it is a lot of questions. I'm not sure what you mean by irrelevant assumptions.

I'm not new to color management, and I am aware of color theory. And I understand the difference between assign and convert. Assign preserves numbers, convert attempts to preserve appearance

I will restate as 3 concise questions in separate posts.

[Ramón_G_Castañeda]

Printer_Rick wrote:

I'm not new to color management, and I am aware of color theory.

Then you're…

[Ramón_G_Castañeda]

Printer_Rick wrote:

I will restate as 3 concise questions in separate posts.

Not here, please.

Post in the Color Management forum, where this discussion belongs.

[BTyson]

@ Ramón_G_Castañeda      GET.    LOST.

Referring to the above, patently impatient, insulting, unhelpful remarks and demeaning tone. Even if more than a decade ago.

[NB, colourmanagement net]

Moved as you requested - I suppose that’s the right place for this discussion. Its all from long ago though

I hope this helps
neil barstow, colourmanagement net :: adobe forum volunteer:: co-author: 'getting colour right'
google me "neil barstow colourmanagement" for lots of free articles on colour management

[Ramón_G_Castañeda]

This excerpt copied and pasted from an old post of mine may help you understand the difference between CONVERT and assign.

To understand profiles, think of your image as text, and of the profile as a tag that indicates in which language the text is written.

If you see text that says GIFT, you need to know whether it's in English or in German. If in German, the word means "poison", if in English, it means a present.

Other examples: ONCE means "eleven" in Spanish but "one time" in English.

MOST means "Bridge" in Russian but "greatest in amount, extent, or degree" in English and "fruit juice" in German.

If you change the language (profile) by ASSIGNING, you change the meaning of the text (appearance of the image). The numbers representing the colors in your image will remain the same, but the colors will change because the same numbers now mean something else (as the meaning of the text will change if you now read the same letters in a different language).

CONVERTING to a profile will preserve the colors while the numbers change, in the same manner as the text will retain its meaning if you TRANSLATE it into a different language, changing the letters but preserving the meaning.

Bottom line:

ASSIGNing a different profile will preserve the numbers and will change the colors of the image;

CONVERTing to a profile will preserve the colors and change the numbers accordingly.

[Printer_Rick]

Ramón G Castañeda wrote:

To understand profiles, think of your image as text, and of the profile as a tag that indicates in which language the text is written.

If you see text that says GIFT, you need to know whether it's in English or in German. If in German, the word means "poison", if in English, it means a present.

Other examples: ONCE means "eleven" in Spanish but "one time" in English.

MOST means "Bridge" in Russian but "greatest in amount, extent, or degree" in English and "fruit juice" in German.

If you change the language (profile) by ASSIGNING, you change the meaning of the text (appearance of the image). The numbers representing the colors in your image will remain the same, but the colors will change because the same numbers now mean something else (as the meaning of the text will change if you now read the same letters in a different language).

CONVERTING to a profile will preserve the colors while the numbers change, in the same manner as the text will retain its meaning if you TRANSLATE it into a different language, changing the letters but preserving the meaning.

Bottom line:

ASSIGNing a different profile will preserve the numbers and will change the colors of the image;

CONVERTing to a profile will preserve the colors and change the numbers accordingly.

Not true, the language analogy falls short. You are suggesting that assigning Adobe RGB to an sRGB image may turn greens to reds, and blues to yellows. And that is not what happens at all.

Words have negative (poison) and positive (gift) values. But there are no "good" or "bad" colors.

And what would Lab be in the language scenario? It's not as if there is a universal language that everyone uses to translate (convert). But there is a universal color space everyone uses to convert.

Furthermore converting does not preserve appearance, it attempts to preserve appearance. Which is not possible when going from a large gamut to a smaller one.

[c.pfaffenbichler]

»Not true, the language analogy falls short. You are suggesting that assigning Adobe RGB to an sRGB image may turn greens to reds, and blues to yellows. And that is not what happens at all.

Words have negative (poison) and positive (gift) values. But there are no "good" or "bad" colors.«

Rick, the language-analogy is one of the best ways to help people understand Color Management I’ve heard so far.

A word’s positive or negative connotations are irrelevant here, because no matter what the word’s perceived meaning, if it’s not congruent with the intended one the communication has to be considered as unsuccessful.

(And in a prepress-context there certainly would have to be »good« and »bad« colors with regard to deviation from target. That’s why proof-printers, screens and presses have to be calibrated, isn’t it?)

But I appreciate that with a file You color-tweak for aesthetic reasons without regard for the original image’s appearance that is irrelevant.

So I don’t want to dispute Your editing-methods, but simply urge You to give the analogy some more thought with regard to color-consistency.

[Printer_Rick]

c.pfaffenbichler wrote:

Rick, the language-analogy is one of the best ways to help people understand Color Management I’ve heard so far.

A word’s positive or negative connotations are irrelevant here, because no matter what the word’s perceived meaning, if it’s not congruent with the intended one the communication has to be considered as unsuccessful.

(And in a prepress-context there certainly would have to be »good« and »bad« colors with regard to deviation from target. That’s why proof-printers, screens and presses have to be calibrated, isn’t it?)

I understand the idea behind the language analogy, just pointing out that many people might not see the correlation.

Color models are mathematical concepts. Printed Lab color values can be measured with a spectrophotometer. Words can't really be measured like this.

And I'll stand by my statement that there are no good or bad colors, not when you look at it objectively. Just like there are no good or bad numbers. A color swatch is either within tolerance (for example ± 2 Delta E (CMC) or not. So right or wrong, maybe, but not good or bad.

If image pixels change in re-assignment according to the language analogy, they might be jumbled beyond recognition. So far I haven't seen that happen.

The language analogy might better be explained

Snow = Blue

In polar regions natives may have 40 words for snow. When a story gets translated (converted) to the tropics 40 words become 3. Just like colors dropping out in a color conversion.

The story gets passed from the tropics to Norwegians. They have 30 words for snow. They don't like the story as they hear it, so they re-write (assign) new words. It's not the truth anymore, but they don't care, they like the new story

I'm not suggesting this analogy is better. I'm not trying to shoot down the Ramón's analogy. I'm just saying everyone has there own way of understanding a concept. One person might compare color gamuts to different size buckets. Someone else might compare images to audio files. Who knows? It's a complex subject.

[Ramón_G_Castañeda]

Printer_Rick wrote:

…My monitor RGB profile has a gamma of 1.8 (mac standard).

You are living in the stone age.  Gamma 1.8 is a relic left over from the day of monochrome monitors and black-and-white LaserWriter printers.  It has nothing to do with colors.  Pros have been using gamma 2.2 for years and years.  Even Apple recommends it.

As a matter of fact, the default value in the upcoming Leopard (OS 10.6) due in September will in fact be gamma 2.2.

[Ramón_G_Castañeda]

Printer_Rick wrote:

They are of course both triangles, I believe all RGB gamuts are.

WRONG.  Profiles are complex three-dimensional bodies in space.  You're looking at a simplified 2-dimensional projection on a single plane that tells you very little.

Printer_Rick wrote:

I have a profile editor that can view both of these …

My suggestion would be to put it away for now, until you have learned a bit more about color theory and color management.  Now it's just confusing you—massively, apparently.

(Sorry if you are in fact a printer by profession, as your user ID suggests.  I don't mean to offend you, but you need to do a lot of studying.)

As a matter of fact, I'll stop right here.  I can see it would take way more time than I have to read the rest of your post and straighten out your misconceptions.

PS— sRGB is the lowest common denominator, where the "s" stands for sh¡t.

[Ramón_G_Castañeda]

Finally, you should know that there is a dedicated Color Management forum in these Adobe forums, and that's where this type of discussions belongs—not here, really.

http://forums.adobe.com/community/design_development/color_management#

[Printer_Rick]

Finally, you should know that there is a dedicated Color Management forum in these Adobe forums, and that's where this type of discussions belongs—not here, really.

My color management questions were related to images and therefore Photoshop. On another note, if it doesn't belong, why did you reply more than 10 times? You could have ignored my post.

As a matter of fact, the default value in the upcoming Leopard (OS 10.6) due in September will in fact be gamma 2.2.

So what you're saying is, 2.2 is not currently the default. So what is the current mac default? I wonder...

ASSIGN is there so you can make educated guesses as to what color space an untagged file was created handed to you by a moron.  When you run into such a moron who does not embed the profile in his images, first cycle through possible color profiles in the ASSIGN dialog box until you make and educated guess by finding the one profile that makes the image look most plausible, then go beat up the moron who handed you that file with a baseball bat.

And what if a moron unwittingly embedded the wrong profile in output? Then assigning a different one would restore the original color.

PS— sRGB is the lowest common denominator, where the "s" stands for sh¡t.

sRGB is Adobe's default RGB color space. It is the standard for world wide web. It is used by Pantone. In short it is the RGB profile most commonly encountered

I will re-iterate it's not my working RGB space, I don't care for it, I don't consider it ideal for CMYK conversion.

[Miguel_Curto]

Printer_Rick wrote:

sRGB is Adobe's default RGB color space. It is the standard for world wide web. It is used by Pantone. In short it is the RGB profile most commonly encountered

I will re-iterate it's not my working RGB space, I don't care for it, I don't consider it ideal for CMYK conversion.

The idea that sRGB is the most common profile is a misconception.That profile was created to simulate an uncalibrated enviroment (monitor).Thats why if you use Photoshop function "Save for Web" it converts to sRGB then strips profile information.And this is only because until recently most web browsers didnt have any Color Management.I know Firefox has but the others until recently didnt (might be diferent know thought).

If its used by Pantone or not I dont know,but if it is I would like to know why and for what purpose cause it doesnt make any sense...

Its not ideal for any print (CMYK convertion) since it's very narrow gamut will most probably clip many satured colors.

The only good thing about it (besides being a grey balanced profile) is that you can be sure the person you send it too will not see many variations (shifts) in color from what youre seing on your calibrated monitor using Photoshop or any other ICC aware aplication.Thats why I always send previews of work in sRGB, because most of the time people that have to evaluate it dont even bother to open them in Photoshop,they use e-mail programs or browsers,let alone calibrated/profiled monitors.

I think the idea behind making it default is just that,being on the safe side.People that are aware of that ussually change it unless theyre working mainly for the Web.

This and much more you can find on the links about Bruce Fraser.He made great contributions to make people aware of Color Management.

Hope this helps.

Especificaly u can read this one:

http://www.creativepro.com/article/out-of-gamut-getting-a-handle-on-color-management

Images on examples are self-explanatory.

[Printer_Rick]

Thanks for the input

When saying sRGB is the most common profile, I meant it's the one I see most. My RGB policy is set to preserve embedded. The VAST majority of images I receive from clients use this profile. My thinking is most designers do not change the default color settings (North America general purpose)

Usually when I open these sRGB images, reassign Adobe RGB, then convert to CMYK, the result is much better than sRGB - CMYK. If my RGB policy was set to Off, I would get the same effect as re-assigning - my working space is Adobe RGB.

I'll add I only throw out the embedded sRGB if the the customer requests pleasing color, and the proof preview is crud. Otherwise I have to honor the sRGB.

[Miguel_Curto]

Printer_Rick wrote:

When saying sRGB is the most common profile, I meant it's the one I see most. My RGB policy is set to preserve embedded. The VAST majority of images I receive from clients use this profile. My thinking is most designers do not change the default color settings (North America general purpose)

Usually when I open these sRGB images, reassign Adobe RGB, then convert to CMYK, the result is much better than sRGB - CMYK. If my RGB policy was set to Off, I would get the same effect as re-assigning - my working space is Adobe RGB.

I'll add I only throw out the embedded sRGB if the the customer requests pleasing color, and the proof preview is crud. Otherwise I have to honor the sRGB.

http://www.creativepro.com/files/story_images/Fig_1.jpg

To make this example I would have one patch of color (in Adobe RGB or even sRGB)and dulicate it 3 times.Then would leave original alone and CONVERT the others to Scanner,Monitor and Printer Profiles.But in Photoshop they all look alike (like this one bellow):

http://www.creativepro.com/files/story_images/Fig_2.jpg

To publish this example (in Fig1) I would have to "break" Color Management and "assign to sRGB" all of them so you could actually see the diference how that particular value of RGB is renderer in those diferent devices.

The reason your convertion is working is probably beacuse most of the times you receive the images over-saturated...which yelds bad results in straight conversion to CMYK because off out-of-gamut colors (altought you can try Perceptual renderings if you have many diferent colors).When you assign sRGB values to Adobe RGB youre actually (among other things) de-saturating de images.

[Printer_Rick]

Miguel Curto wrote:

To make this example I would have one patch of color (in Adobe RGB or even sRGB)and dulicate it 3 times.Then would leave original alone and CONVERT the others to Scanner,Monitor and Printer Profiles.But in Photoshop they all look alike (like this one bellow):

I already know that conversion in these cases preserves on-screen appearance.

The reason your convertion is working is probably beacuse most of the times you receive the images over-saturated...which yelds bad results in straight conversion to CMYK because off out-of-gamut colors (altought you can try Perceptual renderings if you have many diferent colors).When you assign sRGB values to Adobe RGB youre actually (among other things) de-saturating de images.

No, the opposite. I receive the sRGB. Assign Adobe RGB. Color is expanded.

[Miguel_Curto]

Printer_Rick wrote:

No, the opposite. I receive the sRGB. Assign Adobe RGB. Color is expanded.

Actually no.Since Adobe RGB is much larger than sRGB if youre assigning sRGB values to Adobe RGB you end up"with lots of free space".

PS- Im not hangered in any way... this is a "healthy" discussion...the objective of this forums I think.We dont have to agree but many people come here and they should get facts straight...

[Ramón_G_Castañeda]

It's useless, Miguel.  Anyone with an IQ above room temperature and a modicum of understanding of color theory can easily spot the blatant fallacies this [edited by host]  guy keeps coming up with, post after post.  I've now plonked him, so I don't even see his posts at all.

[Miguel_Curto]

Ramón G Castañeda wrote:

It's useless, Miguel.  Anyone with an IQ above room temperature and a modicum of understanding of color theory can easily spot the blatant fallacies this guy keeps coming up, post after post.  I've now plonked him, so I don't even see his posts at all.

Im not on a mission,but this is the kind of things im used to discuss with my clients whenever they demand work delivered in CMYK.So its kind of a personal thing to desmistify some of this miths.

No harm or agravation intended.It was only half a dozen years back when I read that book I mentioned I got a full perspective on Color Management.

[Printer_Rick]

Miguel Curto wrote:

Actually no.Since Adobe RGB is much larger than sRGB if youre assigning sRGB values to Adobe RGB you end up"with lots of free space".

PS- Im not hangered in any way... this is a "healthy" discussion...the objective of this forums I think.We dont have to agree but many people come here and they should get facts straight...

Thanks for that Miguel, I appreciate it. I did not post my original questions to anger anyone

I should clarify. I receive an sRGB image. I assign Adobe RGB. On-screen the color is more saturated. This saturation carries over into the subsequent CMYK conversion.

Try it with any sRGB image. Convert to CMYK, save a copy. Then assign Adobe RGB, convert to CMYK. Compare the two CMYK images, I think you'll see what I mean.

It is not a specific color correction by any stretch, but it's not random rearranging of colors either.

[Was DYP]

I did not post my original questions to anger anyone

Most of us have angered Ramón over the years. It is very easy to do to [his: edited by host] way of thinking.

Count that as a badge of honor! Most of us have already earned that.

"I've now plonked him, so I don't even see his posts at all."  - He has done that to me and I am so thankful. It is just that he does not always keep his promises.