Assign Profile vs. Convert to Profile?

Discussion in 'Photoshop Tutorials' started by C Wright, Dec 29, 2005.

  1. C Wright

    C Wright Guest

    I am a bit confused regarding the appropriate use of the 'Assign to Profile'
    versus the 'Convert to Profile' functions on the Photoshop Edit menu.
    I think that I understand the basic differences in function, that is the
    'Assign' command simply assigns a different color space with out actually
    converting any colors to to different numerical values within the new color
    space. While the 'Convert' command actually converts colors to different
    numerical values in the new color space. But, when is it appropriate to use
    one command over the other?

    If, for example, I am preparing an image edited in the Adobe RGB color
    space, for the web or for a lab, where sRGB is required is it not necessary
    to use the convert function? Will the assign function work equally well?

    It would appear obvious that conversions to radically different color spaces
    would require the use of the convert function. But, if the assign function
    would not even be appropriate for less radical conversions like aRGB to sRGB
    then what is it for?
    Chuck
     
    C Wright, Dec 29, 2005
    #1
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  2. C Wright

    Bill Hilton Guest

    C Wright wrights ...
    I think everyone has problems with this at first ...
    You got it ...
    I have a friend who is struggling to learn this as well so I put
    together two jpegs as teaching aids, feel free to download them and
    make the assignments when you open them in Photoshop to see the
    differences ... basically I converted a RAW file in 'ProPhoto' working
    space, which has a very wide gamut, and marked off an area of bright
    red that I measure as 144/89/46 ... then I converted a copy to sRGB in
    preparation for 'save for web' and when I convert the red area becomes
    something like 200/77/39 in sRGB ... then I made jpegs of both files
    using 'save for web', which drops off both working space profiles.

    When you view these on the web in a non-color managed browser the sRGB
    version looks pretty close to right since that's what sRGB was designed
    for, but the ProPhoto version looks dull because 144/89/46 means "RED"
    in ProPhoto space but "blah crappy red" without the profile. You can
    download both of these and then open them in Photoshop and assign
    different working spaces each time you open one and see the effect this
    has, but basically if you assign 'ProPhoto' as working space to the
    144/89/46 one it looks good, as does assigning 'sRGB' to the already
    converted one. Here are the files if you want to look and try this ...
    http://members.aol.com/bhilton665/hilton_srgb.jpg
    http://members.aol.com/bhilton665/hilton_prophoto.jpg

    Hope this helps ...
    I would *always* convert when going from AdobeRGB to sRGB since the
    numeric values mean different colors. The example I used is more
    extreme because ProPhoto is a wider space (so saturated "red" has lower
    RGB values) but you'll still see something similar to what my examples
    show, especially with saturated colors ... it won't be as obvious but
    you'll typically see a difference. In a few minutes I'll put up the
    AdobeRGB version if you wish, it should be somewhere between the
    ProPhoto and sRGB versions though.
    Yes, this is what my ProPhoto example was meant to show ...
    I stumbled over this when I was making web images of landscape photos
    of the "red rock country" in the desert southwest ... I was selling
    prints so needed the web images to look as similar to the print images
    as possible and taking Ektaspace or AdobeRGB files directly to the web
    would often kill the colors, so I eventually figured out why. So my
    final point would be that for some colors you won't see much of a
    difference if you convert AdobeRGB files directly using 'save for web',
    but with reds and oranges and some other saturated colors you'll see a
    big change compared to first dumbing them down to sRGB ... so I just
    always do the conversion to sRGB now before running 'save for web'.

    Bill
     
    Bill Hilton, Dec 29, 2005
    #2
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  3. C Wright

    Mike Russell Guest

    The rule of thumb is this: "convert" is used when you want to preserve the
    appearance of the image, and "assign" is used when you want to change the
    appearance of the image.
    You would use convert. If you assign sRGB to an Adobe RGB image, the colors
    will be less saturated.
    Probably the most common use of the assign function is to compensate for
    someone else's error or omission . There are other uses. For example, an
    easy way to bump overall saturation is to convert to sRGB, and then assign
    Adobe RGB or even ProPhoto RGB.

    There are other uses, again involving changing the appearance of the image
    as part of a color editing operation. Profile assignment is an effective
    way to manipulate certain images. An operation called "pseudo profiling"
    can be very effective in rescuing very underexposed images. In this
    procedure, a "pseudo profile" is created by modifying Adobe RGB with a very
    high gamma value of 20 or so. When this is assigned to an underexposed
    image, the color and contrast can be boosted significantly. This technique
    was introduced, AFAIK, by Dan Margulis, and appears in his latest
    Professional Photoshop book.
     
    Mike Russell, Dec 29, 2005
    #3
  4. C Wright

    Bill Hilton Guest

    I wrote ...
    http://members.aol.com/bhilton665/hilton_adobergb.jpg ... so if you
    download this one and assign the right profile when you open it then it
    will look correct ... if you open all three of these at once in a web
    browser you can see the difference between dropping the ICC profiles
    for different gamut 'working spaces'.

    Bill
     
    Bill Hilton, Dec 29, 2005
    #4
  5. I agree with everything stated previously :)

    One more common use for 'assign profile' is if you've had a custom
    profile made for an input device (scanner or camera). In this case, the
    image will probably arrive at your computer in sRGB (or sometimes
    AdobeRGB), so you assign the correct device profile. The original
    profile is approximate interpretation of the RGB values, but by
    assigning the device profile you are interpreting the values more
    accurately.
     
    Graeme Cogger, Dec 29, 2005
    #5
  6. C Wright

    C Wright Guest

    Thanks to all for the very clear answers. And, Bill, I downloaded all three
    images that you posted and played with the profiles; the the changes do
    indeed make some pretty dramatic differences - thanks!
    Chuck
     
    C Wright, Dec 29, 2005
    #6
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