Converting from AdobeRGB to SRGB

Discussion in 'Digital Photography' started by Alfred Molon, May 12, 2006.

  1. Alfred Molon

    Alfred Molon Guest

    Suppose you convert a RAW image to JPEG using the AdobeRGB colour space
    and save it. If you then convert it to SRGB for web display, you might
    end up with clipped highlights or burnt shadows, because AdobeRGB has
    more dynamic range than SRGB. Is this correct?
    --

    Alfred Molon
    ------------------------------
    Olympus 50X0, 7070, 8080, E300, E330 and E500 forum at
    http://groups.yahoo.com/group/MyOlympus/
    Olympus E330 resource - http://myolympus.org/E330/
     
    Alfred Molon, May 12, 2006
    #1
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  2. Alfred Molon

    Jim Guest

    "Alfred Molon" <> wrote in message
    news:...
    > Suppose you convert a RAW image to JPEG using the AdobeRGB colour space
    > and save it. If you then convert it to SRGB for web display, you might
    > end up with clipped highlights or burnt shadows, because AdobeRGB has
    > more dynamic range than SRGB. Is this correct?
    > --
    >
    > Alfred Molon
    > ------------------------------
    > Olympus 50X0, 7070, 8080, E300, E330 and E500 forum at
    > http://groups.yahoo.com/group/MyOlympus/
    > Olympus E330 resource - http://myolympus.org/E330/

    No. The difference is that the gamut of sRGB is smaller than that of Adobe
    RGB. This means that some colors in AdobeRGB can only be approximated in
    sRGB. You might be hard pressed to see the difference.
    Jim
     
    Jim, May 12, 2006
    #2
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  3. Alfred Molon

    Alfred Molon Guest

    In article <au69g.70158$>,
    says...

    > No. The difference is that the gamut of sRGB is smaller than that of Adobe
    > RGB. This means that some colors in AdobeRGB can only be approximated in
    > sRGB. You might be hard pressed to see the difference.


    But if a colour is out of gamut, it should be clipped, shouldn't it?
    When you convert a RAW image with lots of dynamic range, it can happen
    that the blown highlights indicator pops out if you choose SRGB and not
    if you choose Adobe RGB.
    --

    Alfred Molon
    ------------------------------
    Olympus 50X0, 7070, 8080, E300, E330 and E500 forum at
    http://groups.yahoo.com/group/MyOlympus/
    Olympus E330 resource - http://myolympus.org/E330/
     
    Alfred Molon, May 12, 2006
    #3
  4. Alfred Molon

    Jim Guest

    "Alfred Molon" <> wrote in message
    news:...
    > In article <au69g.70158$>,
    > says...
    >
    >> No. The difference is that the gamut of sRGB is smaller than that of
    >> Adobe
    >> RGB. This means that some colors in AdobeRGB can only be approximated in
    >> sRGB. You might be hard pressed to see the difference.

    >
    > But if a colour is out of gamut, it should be clipped, shouldn't it?

    It is not necessarily a good idea to merely clip the color at the edge of
    the gamut.
    In any case, clipping is just one method of aproximating out of gamut
    colors.
    Jim
     
    Jim, May 13, 2006
    #4
  5. Alfred Molon

    Stacey Guest

    Alfred Molon wrote:

    > In article <au69g.70158$>,
    > says...
    >
    >> No. The difference is that the gamut of sRGB is smaller than that of
    >> Adobe
    >> RGB. This means that some colors in AdobeRGB can only be approximated in
    >> sRGB. You might be hard pressed to see the difference.

    >
    > But if a colour is out of gamut, it should be clipped, shouldn't it?
    > When you convert a RAW image with lots of dynamic range, it can happen
    > that the blown highlights indicator pops out if you choose SRGB and not
    > if you choose Adobe RGB.


    I'm not going to try to explain why converting from aRGB to sRGB doesn't act
    this way, but it ussually doesn't. The only time I've seen the difference
    on a monitor is when the color in aRGB is WAY out there, like with a really
    saturated blue or yellow. I had to work to get this image to look OK in
    sRGB because of how vivid this yellow is.

    http://img.villagephotos.com/p/2005-1/937049/springweb2.jpg

    When I run into this, I use soft proofing with gamut warning enabled and
    then desaturate the specific color till it "gets in line"..

    --

    Stacey
     
    Stacey, May 13, 2006
    #5
  6. Alfred Molon

    Alfred Molon Guest

    In article <>, says...

    > I'm not going to try to explain why converting from aRGB to sRGB doesn't act
    > this way, but it ussually doesn't. The only time I've seen the difference
    > on a monitor is when the color in aRGB is WAY out there, like with a really
    > saturated blue or yellow. I had to work to get this image to look OK in
    > sRGB because of how vivid this yellow is.
    >
    > http://img.villagephotos.com/p/2005-1/937049/springweb2.jpg
    >
    > When I run into this, I use soft proofing with gamut warning enabled and
    > then desaturate the specific color till it "gets in line"..


    That's what I meant. When the image contains a lot of dynamic range,
    with highlights close to 255 or even brighter, in Adobe RGB the image
    might not have clipped highlights, when in SRGB they are clipped.
    --

    Alfred Molon
    ------------------------------
    Olympus 50X0, 7070, 8080, E300, E330 and E500 forum at
    http://groups.yahoo.com/group/MyOlympus/
    Olympus E330 resource - http://myolympus.org/E330/
     
    Alfred Molon, May 13, 2006
    #6
  7. Alfred Molon

    W (winhag) Guest

    Yes, I agree this can happen. I have seen a more obvious 'version' of
    this when using ProPhoto (larger gamut than AdobeRGB1998). I had a RAW
    file which had bright orange/red elements (fall foiliage in the sun).
    It did not clip in ProPhoto, but clipped in aRGB and sRGB when using
    Adobe Capture Raw.

    Alfred Molon wrote:
    > In article <>, says...
    >
    > > I'm not going to try to explain why converting from aRGB to sRGB doesn't act
    > > this way, but it ussually doesn't. The only time I've seen the difference
    > > on a monitor is when the color in aRGB is WAY out there, like with a really
    > > saturated blue or yellow. I had to work to get this image to look OK in
    > > sRGB because of how vivid this yellow is.
    > >
    > > http://img.villagephotos.com/p/2005-1/937049/springweb2.jpg
    > >
    > > When I run into this, I use soft proofing with gamut warning enabled and
    > > then desaturate the specific color till it "gets in line"..

    >
    > That's what I meant. When the image contains a lot of dynamic range,
    > with highlights close to 255 or even brighter, in Adobe RGB the image
    > might not have clipped highlights, when in SRGB they are clipped.
    > --
    >
    > Alfred Molon
    > ------------------------------
    > Olympus 50X0, 7070, 8080, E300, E330 and E500 forum at
    > http://groups.yahoo.com/group/MyOlympus/
    > Olympus E330 resource - http://myolympus.org/E330/
     
    W (winhag), May 13, 2006
    #7
  8. Alfred Molon

    Stacey Guest

    Alfred Molon wrote:

    > In article <>, says...
    >
    >> I'm not going to try to explain why converting from aRGB to sRGB doesn't
    >> act this way, but it ussually doesn't. The only time I've seen the
    >> difference on a monitor is when the color in aRGB is WAY out there, like
    >> with a really saturated blue or yellow. I had to work to get this image
    >> to look OK in sRGB because of how vivid this yellow is.
    >>
    >> http://img.villagephotos.com/p/2005-1/937049/springweb2.jpg
    >>
    >> When I run into this, I use soft proofing with gamut warning enabled and
    >> then desaturate the specific color till it "gets in line"..

    >
    > That's what I meant. When the image contains a lot of dynamic range,
    > with highlights close to 255 or even brighter, in Adobe RGB the image
    > might not have clipped highlights, when in SRGB they are clipped.


    I'd develop the image in aRGB and then figure out how to desaturate the
    specific problem color to get it back inside sRGB withough clipping. I've
    also found sometime converting using "saturated" intent will work when this
    is a problem to avoid clipping saturated colors to white when only one
    specific color is a problem.
    --

    Stacey
     
    Stacey, May 14, 2006
    #8
  9. Alfred Molon wrote:
    > In article <>, says...


    >> The only time I've seen the difference
    >> on a monitor is when the color in aRGB is WAY out there, like with a really
    >> saturated blue or yellow. I had to work to get this image to look OK in
    >> sRGB because of how vivid this yellow is.
    >>
    >> http://img.villagephotos.com/p/2005-1/937049/springweb2.jpg


    I'd love to see an sRGB and an aRGB JPEG of this image, just for kicks.

    > That's what I meant. When the image contains a lot of dynamic range,
    > with highlights close to 255 or even brighter, in Adobe RGB the image
    > might not have clipped highlights, when in SRGB they are clipped.


    There are no highlights brighter than 255 (in 8bit). The difference
    between gamuts is what those RGB 3-tuples mean in reality. Display
    devices can potentially produce many more colours than (0,0,0) to
    (255,255,255), i.e. about 1.68 million RGB combinations. Some can
    produce more colours in one or two channels, and less in another.

    A colour space is a specific defined choice of how the (0,0,0) to
    (255,255,255) range of colours should be positioned within the envelope
    the display device (even a theoretical one) provides. The aRGB space
    maps the available values onto a wide range of colours, with bugger gaps
    (steps) between colours than sRGB. ProPhoto is much wider than aRGB
    again, with gaps so big it doesn't work well for 8bit at all, but is
    excellent for 16bit (i.e. (0,0,0) to (65535,65535,65535)).

    All of these represent theoretical display devices. Real devices
    (monitors, printer/paper combinations, etc) have their own specific
    colour spaces, described by ICC profiles.

    Conversion between colour spaces means finding a mapping in the
    destination colour space that makes the majority of images look like
    they did in the original colour space as much as possible. "Look like"
    is a flexible concept and depends on what you're after (same numeric
    gradations, human perception, etc). That's why you're usually asked for
    a rendering intent when converting to a target colour space.

    Clipping isn't going to be a useful conversion strategy between aRGB and
    sRGB in most cases. In the end, all depends on the gamut of the output
    device. If it lies inside of both aRGB and sRGB, a conversion from aRGB
    to sRGB before finally converting to the device colour space is probably
    meaningless. If the device colour space is larger (in some areas at
    least) than sRGB, you end up short-changing yourself (for the sake of
    compatibility) if you convert from aRGB to sRGB.

    Cheers
    Steffen.
     
    Steffen Kluge, May 16, 2006
    #9
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