Assign- Convert - Proof Colors

>> I beg to differ (about Conversions degrade color information)...There is nothing "degraded" about a well-done conversion

Hmm... you may be right, Marco.

I recall I got that bit of info in one of my forum discussions with Bruce Fraser or from one of his books, but I hope I am not confusing people with my recollections.

To a lay person (like me) who is trying to conceptualize the basic theory that Converting a higher-gamut space like Adobe RGB or ProPhotoRGB to smaller-gamut spaces like a press CMYK or web sRGB space would have to clip or compress and/or stir up some colors to happen I guess that would be the basis of my point.

In any case, it is probably a good idea for most people to make as few profile Conversions as possible based on simple common sense principles like if we Convert AdobeRGB to sRGB -- and back again -- we have probably lost (degraded) some color information that we can never get back.

Let alone if we Assign (or Assume) sRGB to an AdobeRGB file -- hammer it back into shape in CMYK SoftProof mode and save it back out with no profile ;)

How that theory may apply to the actual rocket science is over my pay grade and more likely suited to your technical expertise.

+++++++

BTW
>> Converting to a profile changes the color numbers in the file, but keeps the appearance unchanged (except for gamut mismatches, in which case the rendering intent decides how the out-of-gamut colors in the source are mapped to the destination).

That totally rocks...

csullivan,
>I do have a good understanding of Assign and Convert.

Not wanting to appear rude, condescending or disrespectful, but like Marco, I really question the veracity of that statement. :/

MORE ABOUT ASSIGN PROFILE

Bruce Fraser wrote in a previous Adobe forum:

(You could change profiles a thousand times via Assign Profile and the image would not degrade) "Inasmuch as the numbers in the file wouldn't change, this is true. But it would display incorrectly, and convert to any other space incorrectly, so it's fair to say that while the integrity of the data hasn't been compromised, and you can rescue the file by assigning the correct profile, for all practical purposes, it's hosed."

>> once you have a "translation" (conversion) and you...re-translate back or to a different language (profile) that something may be lost in the translation....

EXACTLY

Conversions degrade color information...I like to keep my color conversions to an absolute minimum.

For example:

Capture in Camera RAW format
Open in Adobe Camera Raw 16-bit ProPhotoRGB
Edit in Adjustment Layers
Save MASTER FILE in that format
Open and resize and Convert to the Target Space
Save the production copy

That leaves my workflow with ONE conversion and fills my production copy with as much color information as possible.

>> I do have a good understanding of Assign and Convert.

if you know (and have Honored) the Source Space in Photoshop, WHY are you still talking about ASSIGNING a different profile to it it is kind of a pointless experiment once you understand the point

if you want to change the Source Space (Source Profile) -- CONVERT

if you want to "Soft Proof" a Target Profile/Space in Photoshop -- use View> Proof SetUp: Target Profile
>> how Photoshop uses previews

The Color Management System CMS CONVERTS the SourceSpace/File/Profile into MonitorRGB (the custom "calibrated" monitor profile) and PROOFs the color accurately on the screen -- this happens on the fly, automatically behind the scenes in Ps (we cannot turn it off since version 6).

The file (the document Source Space) is independent of Photoshop:

The Color Management System CMS, Photoshop, ONLY uses the monitor profile for one thing: To PROOF source file on the monitor (the monitor profile has zero to do with how the file prints).

The Color Management System CMS, Photoshop, ONLY uses the printer (target) profile Print Space for one thing: To PROOF source file on the paper (the printer profile Print Space has zero to do with how the file looks on the monitor)...www.gballard.net/psd/cmstheory.html

Thank you to both of you for technical and non-technical. The analogy of language is very good and would also support the theory that once you have a "translation" (conversion) and you attempt to re-translate back or to a different language (profile) that something may be lost in the translation....

I do have a good understanding of Assign and Convert. Your information just supports that. What I did not know is how Photoshop uses previews.

What I thought was that if a had a ProPhoto RGB file and assigned Adobe RGB that the preview would reflect in gamut colors, which in turn, would look very bad given the differences in size of color space. Convert (From ProPhoto), would actually change the pixel values to fit inside of the gamut of the destination profile (Adobe RGB).

Why is it that:
If all colors in the image from ProPhoto fit inside of the Adobe RGB profile to begin with, that the preview would chaange dramatically. Is it due to the size of the gamut of ProPhoto (i.e. the distance between color values)?

and just for clarification of the preview mode. If I do assign Adobe RGB profile in this instance, why do I not get the choice of rendering intents? I am assuming that the preview is in gamut colors (and others are clipped?)

thanks

I somehow missed that thread, Ramón, but here is one of the best explanations I've read:

Eric Chan - 9:30am Nov 21, 08 PST (#71 of 82)
Camera Raw Engineer

I have not read the whole thread, but the easiest way to think of it is in terms of the language analogy.

Tagging/assigning is identification.

Converting means translation while preserving meaning.

Here's an example.

Suppose you hear a stream of words coming over the radio while driving your car. You don't understand it. Your friend sitting next to you says, "Oh, that sounds like Korean." That's tagging, or assigning. Your friend is identifying what the language is. There's no conversion/translation happening. Your friend may be correct, or incorrect. (For all you know, the real language might actually be Japanese.) Regardless, the central point is that this is what tagging/assigning means.

But now suppose you actually want to understand what those words mean (i.e., what the radio program is about). Then somebody has to translate it for you. This is "conversion." You ask your friend to translate the "Korean" to English, a language you do understand. What you hear from your friend are words in English, which are different from the original words coming over the radio (which are in Korean). But the meaning is the same (**). Going back to color management, "conversion" means that in general the underlying numbers change during the conversion process, but the color appearance stays the same.

Eric

(**) This assumes your friend actually knows Korean and translated it correctly.

csullivan,

The only time you use assign is when some moron hands you an untagged profile and you need to make an educated guess as to which color space said moron was using when he/she created and saved the file.

CONVERT to profile strives to preserve the colors while changing the numbers. Assign maintains the numbers and changes/wrecks the colors.

Maybe this old post will help you:

Ramón G Castañeda, "Definitions for profiles" #3, 16 Nov 2008 5:17 pm

ASSIGN VERSUS CONVERT TO PROFILE
>> Why would the image (change when) assigning the profile, but look the same as the original when converting?

That behavior is 100% to be expected. I like to explain the difference between Assign Profile and Convert To Profile like this: http://www.gballard.net/psd/assignconvert.html

The only time most users ever need to touch Photoshop> Edit> ASSIGN PROFILE is if the Source File is Untagged (and we need to PROOF it and/or edit it in a color-managed application like Photoshop).

On the other hand, Ps> Edit> CONVERT TO PROFILE is a feature most of us use on a daily basis for example, Converting our high-gamut RGB working space to a target CMYK space, an sRGB web space, or a different space (profile) to hand it off.

As a hard general rule, always USE EMBEDDED PROFILE first, then CONVERT TO PROFILE if it is not in the desired color space (profile).

PROOF SETUP

Photoshop> View> Proof SetUp: Profile
AKA "Soft Proofing" is generally used to preview a target device profile (like a specific Printer/Paper/Ink profile, or a specific CMYK press profile).

In most cases, Photoshop's Soft Proofing feature is very confusing in the theory department unless we understand why we are using SoftProofing.

In this case, I would first get the Assign-Convert theory nailed down...and use Proof SetUp as sparingly as possible.

BRUCE FRASER wrote the book(s) on Proof SetUp (Soft Proofing in Photoshop) http://www.creativepro.com/articles/author/127446

Yes, I believe a know the difference.

In simple terms, I believe that assigning a profile, assigns a working "set of colors" (color space) for the person who is correcting. It does not change the color value of the pixels, but is simply a visual reprsentation of the image when confined to the assigned colors. and by embedding it, the next user down the pike will know which defined "color set" was used to make corrections. Converting actually will map colors from one space to another and uses the actual destination spaces pixel values in the file.... right?

If this is the case....
I still ask the question above