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Thread: PCS, sRGB, CIE XYZ, CIE Lab

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    Junior Member David is on a distinguished road
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    PCS, sRGB, CIE XYZ, CIE Lab

    When you create linearization and media profile,you need a EYEone or X-rite equipment.

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    Moderator super silja will become famous soon enough super silja's Avatar
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    Quote Originally Posted by David View Post
    When you create linearization and media profile,you need a EYEone or X-rite equipment.
    you mean spectrophotometer
    eye one is xrite equipment

  3. #3
    shampa
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    Quote Originally Posted by super silja View Post
    Hi aaron125,
    ...Vendors like Heidelberg, EFI, Xrite use CIE Lab or CIE XYZ as pcs.

    sRGB is color space
    sRGB icc profile describe sRGB color space. Everything (from input) is converted inside printer driver to sRGB and after that converted to Printer/media color space. In that way sRGB is PCS
    No, that makes sRGB a working space, not a PCS. In the ICC world the only possible PCS is Lab or XYZ. Outside of ICC, anything is technically possible. But even low end printer drivers don't use sRGB as a working space, just as an input space.

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    Moderator super silja will become famous soon enough super silja's Avatar
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    Quote Originally Posted by shampa View Post
    No, that makes sRGB a working space, not a PCS. In the ICC world the only possible PCS is Lab or XYZ. Outside of ICC, anything is technically possible. But even low end printer drivers don't use sRGB as a working space, just as an input space.
    no, you are wrong,
    think traditionally, monitor-> web offset press, scanner->monitor
    what is working space, what is input, what is output ....
    after that, think , sw->printer driver->printer

    inform yourself about terminology.

    after all conversation i expect that somebody asks, how low end HP/Epson/Canon printer are RGB as everybody knows that they use CMYK cartridges
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  5. #5
    aaron125
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    Quote Originally Posted by super silja View Post
    sRGB icc profile describe sRGB color space. Everything (from input) is converted inside printer driver to sRGB and after that converted to Printer/media color space. In that way sRGB is PCS
    It doesn't matter how the conversion is done, sRGB still cannot ever be considered as a PCS because nothing is actually being converted using sRGB as the PCS because it just isn't possible. A calculation could never be performed using sRGB to convert e.g. ProPhoto -> CMYK without using an actual PCS of either Lab or XYZ. Without an actual PCS, and attempting to use sRGB as the PCS, how would the end CMYK numbers be calculated?

    A PCS is used as an intermediary between 2 colour spaces/profiles & also inside every profile to perform the conversion calculations. The PCS is used to perform the actual calculations on each pixel in an image to arrive at the end numbers for each pixel's RGB/CMYK/etc combination. As all ICC profiles are built with 2 conversion directions, device->PCS & PCS->device, how would sRGB be used as the PCS for e.g. a Lab->CMYK conversion? It just isn't possible.

    I think you may have misunderstood the definition of what a PCS is/does. Referring to the first line I quoted, I don't understand why a driver would convert anything to sRGB prior to converting to the printer output profile? It doesn't make any sense to me & seems illogical because it is absolutely redundant. What would be the actual purpose of converting first to sRGB & then to the printer instead of by-passing the sRGB & going directly to the printer profile? As far as I can tell it doesn't serve any purpose whatsoever because the printer can only print that which is 'allowed' by its own profile. So it wouldn't matter if a particular pixel was initially inside the sRGB gamut or outside sRGB because the final end destination is the same either way - the printer profile.

    I hope that helps clear up any misunderstanding you have about what a PCS is & the function it performs.

  6. #6
    aaron125
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    Quote Originally Posted by super silja View Post
    no, you are wrong,

    inform yourself about terminology.

    after all conversation i expect that somebody asks, how low end HP/Epson/Canon printer are RGB as everybody knows that they use CMYK cartridges
    Even with your super avatar pic (R.I.P. Miles Davis) it is still you who is incorrect & needs to be informed about terminology. Please explain exactly how sRGB may be used as the PCS to determine actual pixel values? That is the function of a PCS.

    What do you mean about low-end printers being RGB when they use CMYK inks? Every printer, from $40 to $40,000+ is an RGB device if used in Windows or Mac with the standard OS drivers. Neither OS is able to process CMYK data so that is the reason all printers are considered RGB devices if being used with standard OS drivers. Nothing at all to do with how much they cost or if they are low-end devices, not sure where you got that from.

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    Moderator super silja will become famous soon enough super silja's Avatar
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    Quote Originally Posted by aaron125 View Post
    It doesn't matter how the conversion is done, sRGB still cannot ever be considered as a PCS because nothing is actually being converted using sRGB as the PCS because it just isn't possible. A calculation could never be performed using sRGB to convert e.g. ProPhoto -> CMYK without using an actual PCS of either Lab or XYZ. Without an actual PCS, and attempting to use sRGB as the PCS, how would the end CMYK numbers be calculated?
    i am surprised with your attitude, you don't know what is sRGB and you continue to speak about color managment color conversion and PCS. I don't like to be rude, but i must to tell you, inform yourself.
    slow down and try to understand what i talking about
    A PCS is used as an intermediary between 2 colour spaces/profiles & also inside every profile to perform the conversion calculations. The PCS is used to perform the actual calculations on each pixel in an image to arrive at the end numbers for each pixel's RGB/CMYK/etc combination. As all ICC profiles are built with 2 conversion directions, device->PCS & PCS->device, how would sRGB be used as the PCS for e.g. a Lab->CMYK conversion? It just isn't possible.
    free your mind, with open mind try to imagine how device links works, there is no PCS in device links, and?
    also ICC use CIE Lab and CIE XYZ for lossless conversion
    when you use printer driver there is no lossless conversion
    I think you may have misunderstood the definition of what a PCS is/does. Referring to the first line I quoted, I don't understand why a driver would convert anything to sRGB prior to converting to the printer output profile? It doesn't make any sense to me & seems illogical because it is absolutely redundant.
    i think that you don't understand definition of PCS, otherwise we will call this intermediate step CIE Lab.
    Don't ask me. grass is green sky is blue. i am not developer. i did not write printer drivers.
    this is how stuff works, Inform yourself.
    What would be the actual purpose of converting first to sRGB & then to the printer instead of by-passing the sRGB & going directly to the printer profile?
    by design, this is how stuff works, why we need device weight (car) 4000 lbs to move 180 lbs (me) from point a to point b

    theoretically:
    Microsoft: Hey HP what kind of monitor you will make. I am seek of thousand different monitors, different phosphors, different colorspace. what you think?
    HP: I prefer sRGB . MS: and printers? HP: what you see is what you get. Printers are sRGB
    MS: Lets everything in my system works in sRGB. Hey what about cameras. HP: sRGB of course
    MS: sRGB rules! HP: sRGB rules! Canon: M$ rules, Epson:M$ rules, Lexmark:M$ rules

    theoretically:
    you have CMYK image in photoshop
    You: click print; Photoshop: hmm, i have cmyk image, hey driver can you print CMYK image. Driver: NOPE, give me sRGB. Photoshop: OK what kind of paper you have? Driver: I don't Know. Give me sRGB image and after that i will find what shall i do. Photoshop: OK here is sRGB data ( CMYK -> LAB -> sRGB)
    Driver: excelent, now i have sRGB image, excellent. What kind of paper i have? Oh premium glossy paper, good, i have lookup table for them. Print!

    (look familiar?)
    As far as I can tell it doesn't serve any purpose whatsoever because the printer can only print that which is 'allowed' by its own profile. So it wouldn't matter if a particular pixel was initially inside the sRGB gamut or outside sRGB because the final end destination is the same either way - the printer profile.
    Don't expect high end RIP for 100$ device. what you expect EFI color managment quality? what is price of sw when you buy 100$ printer, 40$ of inks included :)
    try to print fogra media wedge through printer driver
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  8. #8
    Moderator super silja will become famous soon enough super silja's Avatar
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    Quote Originally Posted by aaron125 View Post
    Even with your super avatar pic (R.I.P. Miles Davis) it is still you who is incorrect & needs to be informed about terminology. Please explain exactly how sRGB may be used as the PCS to determine actual pixel values? That is the function of a PCS.
    Thanks for Avatar
    i already give you answer in my post but i will repeat
    ICC profile specify LUT approach (inform yourself) . You haven't problem to do mapping between two profile.
    123,123,123 map to 144,144,144 what is problem?
    but sRGB is intermediate conversion between input RGB ( whatever ) to output (rgb)
    now you learn that sRGB is color space, not only profile and you can use it as any other CIE XYZ or CIE Lab color space.

    What do you mean about low-end printers being RGB when they use CMYK inks? Every printer, from $40 to $40,000+ is an RGB device if used in Windows or Mac with the standard OS drivers.
    You have q&a in your post
    Neither OS is able to process CMYK data so that is the reason all printers are considered RGB devices if being used with standard OS drivers.
    You have q&a in your post
    Nothing at all to do with how much they cost or if they are low-end devices, not sure where you got that from.
    Low end device come with OS printer driver
    High end device come with EFI
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  9. #9
    shampa
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    Quote Originally Posted by super silja View Post
    now you learn that sRGB is color space, not only profile and you can use it as any other CIE XYZ or CIE Lab color space.
    Yes sRGB is a colour space. (every input/output/working-space profile describes a colour space) It is not a profile connection space.

    The ICC specification explicitly defines Lab and XYZ as the only two PCS. Every input/output/working-space profile defines a conversion between one of the two PCS and another colour space. To convert between two profiles, the colour is first converted from one colour space to the PCS, then from the PCS to the second colour space.

    Low end printer drivers frequently use a working space somewhat larger than sRGB to get nice bright colours and a pleasing look without much care for accuracy. Typical users don't have their monitors set up for accurate colour, and so don't know any different anyway. Most drivers can be set to use sRGB as their input colour space, somewhat limiting gamut, but it is an option that is usually off by default.

  10. #10
    Moderator super silja will become famous soon enough super silja's Avatar
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    Cool

    Quote Originally Posted by shampa View Post
    Yes sRGB is a colour space. (every input/output/working-space profile describes a colour space) It is not a profile connection space.
    tell this to aaron, not to me
    The ICC specification explicitly defines Lab and XYZ as the only two PCS. Every input/output/working-space profile defines a conversion between one of the two PCS and another colour space. To convert between two profiles, the colour is first converted from one colour space to the PCS, then from the PCS to the second colour space.
    there is no need to mention again this, everybody know that
    this is what ICC specify for PCS
    what microsoft specify for PCS is sRGB
    inform yourself
    http://msdn.microsoft.com/en-us/windows/hardware/gg463402
    heading is
    Windows Hardware Developer Center > Learn > Archived White Papers > Colorspace Interchange Using sRGB
    Colorspace Interchange Using sRGB

    accents is on Colorspace Interchange
    and citation from microsoft site, read carefully
    Quote Originally Posted by MS
    So why not just pick CIELAB, for example, to become the interchange space?......
    ......
    One of the important benefits of sRGB is often overlooked or not mentioned by its detractors. That benefit is that most people using personal computers spend a great deal of time either viewing, editing, or otherwise dealing with color data on their screens. Since the sRGB colorspace is or can be quite representative of a majority of displays, data in sRGB can be directly viewed on their monitors without modification. This is an important advantage in that purveyors of color data can place their content in sRGB and know that in most instances when it is viewed on computer monitors it is in a "ready to go" state. No cube roots, table look-ups, or other processing is required.
    .....
    ...
    Aristotle did not likely comprehend the era of digital color, but his statement that "simplicity is the truest elegance" could apply to color imaging as well. I think he would appreciate sRGB.
    please read carefully, everything is explained on MS site.... how and why ...

    after that i hope that you will understand why i said
    Quote Originally Posted by super silja
    take care that printer driver have sRGB PCS (read, small gamut)
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  12. #11
    shampa
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    That article recommends using sRGB as a "colour interchange space" not a PCS. Furthermore it is an old article, and a lot has changed with Windows colour management since then (WCS, scRGB)

    Quote Originally Posted by super silja View Post
    inform yourself

  13. #12
    Moderator super silja will become famous soon enough super silja's Avatar
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    Quote Originally Posted by shampa View Post
    That article recommends using sRGB as a "colour interchange space" not a PCS. Furthermore it is an old article, and a lot has changed with Windows colour management since then (WCS, scRGB)
    If it looks like a duck, and quacks like a duck, we have at least to consider the possibility that we have a small aquatic bird of the family anatidae on our hands
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  14. #13
    shampa
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    Quote Originally Posted by super silja View Post
    If it looks like a duck, and quacks like a duck, we have at least to consider the possibility that we have a small aquatic bird of the family anatidae on our hands
    But it doesn't look or smell like a duck. A PCS is what used as the intermediary when transforming between two profiles. Period. It is not the assumed input colour space (what MS call the colour interchange space) nor is the space where adjustments or processing takes place (The working space). They are different things with different roles.

  15. #14
    Moderator super silja will become famous soon enough super silja's Avatar
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    this is your words
    Quote Originally Posted by shampa View Post
    Every input/output/working-space profile defines a conversion between one of the two PCS and another colour space. To convert between two profiles, the colour is first converted from one colour space to the PCS, then from the PCS to the second colour space.
    .....
    ....

    That article recommends using sRGB as a "colour interchange space"
    you are in conflict with yourself
    read again article


    to aaron125
    what you say about conversion?
    Last edited by super silja; 08-03-2011 at 01:29 PM.
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  16. #15
    shampa
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    Quote Originally Posted by super silja View Post
    this is your words
    you are in conflict with yourself
    read again article
    What has it changed? Where is the conflict?

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