what is colour space?

Discussion in 'Digital Photography' started by fake name, Mar 2, 2004.

  1. fake name

    fake name Guest

    what is the difference between sRGB and Adobe RGB ???
     
    fake name, Mar 2, 2004
    #1
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  2. fake name

    jpc Guest

    First what is color space.

    Your eye can pick out a wide range of colors--maybe several thousand
    different shades of red for instance. In your typical jpg image there
    are only 256 shades of red since it is a 8 bit per color channel
    image. Color space is the system that decides which of the thousands
    of real world red shades you assign to the 256 pixel values in your
    digitized image.

    sRGB is the default color space that most consumer cameras, inkjet
    printers and PC software use. Adobe RGB is mostly used by professional
    photographers when the pictures are to by reproduced on four color
    presses.

    Others may argue differently but unless you have serious money
    invested in printers that can handle a wide color gamut or are doing
    professional repro work I've never seen any reason to switch from sRGB

    jpc
     
    jpc, Mar 2, 2004
    #2
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  3. fake name

    Tom Monego Guest

    I
    Good explanation but one of the reasons digital photos look flat and lifeless
    is sRGB. Adobe 1998 prints wonderfully out of an inkjet printer, the consumer
    processors are locked into sRGB so for traditional photo printing this is what
    you have to use. sRGB is a very truncated safe color space, Adobe 1998 I feel
    is a much more natural looking color space.

    Tom
     
    Tom Monego, Mar 2, 2004
    #3
  4. fake name

    Flycaster Guest

    Strictly speaking, gamut size: ARGB98 is a larger colorspace than sRGB.
     
    Flycaster, Mar 2, 2004
    #4
  5. fake name

    jpc Guest


    What printer are you using? I've never seen much difference but I
    only got a three color printer.

    jpc
     
    jpc, Mar 2, 2004
    #5
  6. fake name

    mark_digital Guest

    Could you explain "Adobe 1998 prints wonderfully out of an inkjet printer,
    the consumer
    processors are locked into sRGB so for traditional photo printing this is
    what
    you have to use." a little further? What is a consumer processor?
     
    mark_digital, Mar 3, 2004
    #6
  7. fake name

    Bill Hilton Guest

    From: "mark_digital"
    He means the printers used by the on-line print processors and the quickie
    places like Wal-Mart or Costco ... often the Fuji models. They are optimized
    for sRGB because most of the people using them send in jpegs in sRGB space.
    None of the high end custom digital print shops using LightJets or Chromiras
    use sRGB though. You can draw the film analogy between people shooting C-41
    neg films and printing 4x6" at the local One Hour Photo or their grocery store,
    vs the people shooting Velvia slide film and paying more for custom Ilfochrome
    prints, for example.

    If you want to see a difference between sRGB and Adobe RGB open a new blank
    file in Photoshop with AdobeRGB as the working space and draw four boxes and
    fill each separately with shades of red, ie, RGB = 210/0/0, then 220/0/0, then
    230/0/0, then 240/0/0. If your monitor is calibrated properly you can see a
    difference between these shades of red (or at least I can on my monitor).

    Now do Image > Duplicate to make an exact copy and on this new one do Image >
    Mode > Convert to Profile and convert to sRGB. Use the eyedropper tool to
    meaure the patches and you'll see that the three reddest ones have clipped to
    R=255 and you can't tell them apart as they are now identical, while the 210
    patch is now 245. Basically any shades or tones of red between 220 and 255 are
    now smushed together into one single red tone. You have more shades of colors
    with AdobeRGB.
    A good inkjet printer like the 6 or 7 color models from Canon, Epson and HP can
    capture the nuances in tonality that AdobeRGB can hold (see the above
    experiment). It's a question of color gamut and these printers (and the
    LightJet and Chromira models mentioned earlier) have a wide enough gamut to
    take advantage of the extra shades of color.

    Bill
     
    Bill Hilton, Mar 3, 2004
    #7
  8. fake name

    jpc Guest

    I agree that if you go from an image created in a color space with a
    wide gamut like AdebeRGB into a color space with a narrower gamut like
    SRGB you will compress the more intense colors just as your experiment
    demonstrates.

    What I don't see is what you gain when you go in the other direction.
    Like the vast majority of digital camera, my camera will only captured
    the image in sRGB. It also does a reasonablely decent job of
    converting the vast majority of colors I see in the real world into
    the colors I see on my monitor--something I've determined
    experimentally by photographing paint samples.

    So if I go to the trouble of converting the image to AdobeRGB what
    happens? I may have a bigger color space to play around in but the
    range of colors in my image won't include the very intense reds,
    greens and blues availabe in the new color space. Which, by the way,
    are colors that are very hard to find in the real world.

    Like I said in my first post if you have serious money invested in a
    very high end camera and printer that can take advantage of AdobeRGB
    go for it. For the rest of us IMHO it is more hassle than gain

    jpc
     
    jpc, Mar 4, 2004
    #8
  9. fake name

    mark_digital Guest

    I'm lazy this morning so I opened Thai Boat sample Adobe provides and I
    applied the Adobe 1998 profile to it. The top of the boat changed
    drastically. But when I wanted to see what was out of gammut the top of the
    boat was selected. So what's the point? What am I not understanding here?
     
    mark_digital, Mar 4, 2004
    #9
  10. fake name

    jpc Guest

    Where did you get the image and what is the file name. I'm using
    photoshop 7 and it isn't in the sample folder on my computer. The
    only boat image is called morning glory and it doesn't change when I
    converted to AdobeRGB

    jpc
     
    jpc, Mar 4, 2004
    #10
  11. fake name

    Bill Hilton Guest

    I agree with you, I never convert from a narrow gamut space to a wider one
    either.
    I guess it depends on the source of your input data ... if your camera will
    only capture in sRGB then that's what you've got to work with.

    People with film scanners (like me) can capture colors even wider than AdobeRGB
    and I often use Joe Holmes' Ektaspace as my film scan profile for saturated
    films like Velvia since he designed Ektaspace to match the gamut of color slide
    film.

    People with newer digital cameras often have the option of tagging files with
    Adobe RGB too, my wife uses a Canon 10D and shoots RAW and we always use the
    ARGB option on those.
    I agree there's little or no point in converting from sRGB to AdobeRGB in a
    situation like yours, BUT for many of us the wider gamut option is available
    directly, ie, from a scanner or higher-end digital camera.
    I do and I am.
    I agree ... the guy making the post was asking for the differences and I was
    explaining them. Once someone understands the trade-offs it's up to them to
    make their choice :)

    Bill
     
    Bill Hilton, Mar 4, 2004
    #11
  12. fake name

    Bill Hilton Guest

    From: "mark_digital"
    If you just do View > Gamut Warning you'll get a warning for the default CMYK
    option as selected in your Color Preferences settings. This is a very limited
    gamut and a lot of colors may be out of gamut quickly.

    If you have a profile for a good printer like a LightJet or a Chromira (you can
    download these free from companies like West Coast Imaging or Calypso) or an
    Epson 2200 profile for the glossy papers you'll see the gamut is much wider and
    many colors that are OOG for CMYK are in gamut for those printers. You can
    check this in Photoshop with View > Proof Setup > Custom and picking the right
    file under "profile" but you have to load these profiles first. This lets you
    compare the gamut of different profiles and you'll quickly see that the wider
    gamut ones keep a lot more colors in gamut.
    "Gamut" is just a range of colors. "Working space" is simply an arbitrarily
    defined gamut that matches up with a range of input/output devices.

    sRGB is a working space created by (I think) HP and Microsoft to emulate the
    gamut of the average, uncalibrated computer monitor and has the narrowest gamut
    of the popular working spaces. It's a good choice for people who shoot digital
    cameras with jpeg files and whose output target is the web or the on-line print
    shops or the quickie printers like Costco or Wal-Mart who use the popular Fuji
    printer, or for those working with a non-color managed graphics program.

    Adobe RGB is a wider gamut working space whose gamut more closely matches
    calibrated monitors, high end digital cameras, scanned film and output devices
    like the high end printers like the LightJet and Chromira or the better 6 or 7
    color photo printers from Epson, Canon and HP. I think it originally was
    designed to match HDTV's gamut.

    There are many other working spaces (you can make your own custom one in
    Photoshop in a few seconds if you know how) designed to match the gamut of
    color slide film or various Apple monitors or Radius Press monitors or
    whatever. Right now most people use sRGB (the Adobe default for "Web Graphics
    Defaults" in the Photoshop color settings) or Adobe RGB (the Adobe default for
    "US Prepress Defaults" in the Photoshop color settings).

    If you work in a wider gamut space you can convert to a narrower space easily
    enough, like a file that's in AdobeRGB for printing but you decide you want to
    make a jpeg of it and put it on the web ... converting this to sRGB will give
    you better results when the file is viewed on an uncalibrated monitor. As jpc
    points out there's nothing to be gained by going the other way, converting a
    narrow gamut file to a wider gamut one.

    There's plenty of good info on the web (and plenty of bad info too,
    unfortunately). Or pick up a good Photoshop book like "Artistry" or "Real
    World" to learn more.

    Bill
     
    Bill Hilton, Mar 4, 2004
    #12
  13. <snip good info>

    Thanks Bill - I've just come into the thread and didn't have much clue
    as to what colour space was all about - though I knew it existed. Now I
    know much more than I did before reading your post.



    Rachael
     
    Rachael of Nex, the Wiccan Rat, Mar 4, 2004
    #13
  14. Because most of my activity is centered around video I have to put my money
    into things like Adobe Premier etc. I use Photoshop 5 and I will have to
    continue doing so for a long long time.
    I used Apple RGB for quite some time and preferred it over sRGB. Then I
    ditched my old monitor for a Syncmaster 955DF (19" Samsung) and started to
    use sRGB because for me it was less of a hassle switching back and forth
    between scans and digital camera images.
    BTW, I dipped into my limited funds and finally bought a APC-Back UPS BX1000
    (600 watts). No Photoshop 7 for me.
     
    mark_digitalĀ©, Mar 4, 2004
    #14
  15. fake name

    andrew29 Guest

    It's the other way around: sRGB is based on HDTV specs. See
    http://www.srgb.com/srgboverview/index.htm

    One other thing thath no-one has mentioned yet. Neither Adobe RGB or
    sRGb are a panacea: inkjet photo printers can print yellows and cyans
    that are outside the range of both Adobe RGB and sRGB. Digital
    cameras can capture colours outside that gamut too.

    Andrew.
     
    andrew29, Mar 5, 2004
    #15
  16. fake name

    jpc Guest

    Great idea for soft proofing high end printers before you even enter
    your local We-Garrantee-to-Confuse photo store. Just don't forget to
    check the simulate paper white and ink black check boxes
     
    jpc, Mar 5, 2004
    #16
  17. fake name

    Bill Hilton Guest

    The "other way around"? So you think sRGB has a wider gamut and Adobe RGB is
    for uncalibrated monitors? You would be the only person I've seen make this
    claim.
    This looks like a HP marketing Power Point presentation, the kind a marketing
    team presents to management or potential customers which puts their "product"
    in the best possible light. They say they are trying to make sRGB work with
    HDTV display conditons (among numerous other display conditons) but that's not
    the same as designing for the full gamut.

    If they really WERE trying to hit the HDTV gamut they apparently failed,
    according to every Photoshop author I've read. Here are a couple of typical
    comments on the differences between sRGB and ARGB from two of the best
    Photoshop books I've read ...

    Barry Haynes, "Photoshop Artistry: A Master Class for Photographers ..." ...
    "The widest gamut of these (built-in working) spaces, Adobe RGB was originally
    a proposed standard for HDTV production. But more importantly, its gamut
    includes essentially the entire CMYK gamut and more because it also better
    encompasses the gamut of things like color RGB film recorders, the LightJet
    5000 digital printer, various Epson and HP printers and other more advanced
    color ouput devices."

    On sRGB Barry says ... "This space is good for people who are primarily working
    on Web images and want to see what they are going to look like on a typical
    monitor. The problem with sRGB is that it is the smallest gamut space ... you
    are potentially throwing out certain colors, even for CMYK print work, and you
    are certainly throwing out colors if you are planning to output to a film
    recorder or LightJet 5000 type digital printer. Photographers working on art
    prints shoud certainly change their RGB working space to something other than
    sRGB"

    One more, from Blatner and Fraser's "Real World Photoshop" ... "The default RGB
    space was sRGB, a color space developed by Hewlett-Packard and Microsoft that
    purports to represent the 'average' monitor. However, we believe that most
    Photoshop users have monitors much better than the sRGB spec, which we think
    represents a really bad 15-inch VGA montitor (the kind you might pick up at a
    garage sale) ... If your work is destined for print, then sRGB is a very poor
    choice indeed".

    I think both of these authors would agree sRGB is right for the new on-line
    print services and the quickie shops using the Fuji Frontier, but for high end
    inkjets and the laser printers like the LightJet or Chromira Adobe RGB is a
    better choice.

    Bill
     
    Bill Hilton, Mar 7, 2004
    #17
  18. fake name

    andrew29 Guest

    No, of course not. Adobe RGB has a wider gamut than sRGB, beyond
    doubt. I'm saying that sRGB is based on HDTV phosphors.

    See www.srgb.com/srgbcolorspacepaper.pdf "High definition television
    or HDTV will use a set of phosphors known as ITU-R 709.BT... From the
    spectral and colorimetric characteristics of these phosphors, a
    standard known as sRGB was proposed and adopted by a number of
    companies such as Hewlett-Packard and Microsoft."
    Bruce Lindbloom sez: "I have heard the rumor that the green primary
    for Adobe RGB came about by the accidental use of the NTSC green
    primary, used incorrectly since NTSC is defined relative to Illuminant
    C while Adobe RGB is defined relative to D65. After the mistake was
    discovered, Adobe decided to keep it since their experiences with this
    accidental reference space were favorable." http://www.brucelindbloom.com/

    Certainly, getting full Adobe RGB on any monitor is very hard: AFAIK
    there's only one monitor in the world that claims to do it, so I doubt
    it's using HDTV green.
    I don't thank anyone disagrees with any of that. The question is not
    which space is the larger, but which is closer to HDTV / ITU-R 709.BT.
    See www.srgb.com/srgb709compatibility.html.

    Andrew.
     
    andrew29, Oct 11, 2004
    #18
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