Chapter 4, Professional Photoshop, 5th Edition

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  • ruttrutt Registered Users Posts: 6,511 Major grins
    edited January 30, 2007
    Hey, man, shoot. I remember that I had to do something like that for this quiz as well. That chapter 1 quiz, on the other hand, well you have to get your head screwed on real tight.
    Myer wrote:
    = = = = =

    I really learned a few tricks here about cause and effect regarding interchanging LAB 'a' and 'b' channels.

    This refers to the quiz on page 84.

    If anybody is interested in this, I'll post the tricks that allowed me to complete the quiz almost flawlessly.

    Otherwise, I won't bother.
    If not now, when?
  • SystemSystem Registered Users Posts: 8,186 moderator
    edited January 30, 2007
    please. I'm game-

    I don't mind cheating on it-
  • MyerMyer Registered Users Posts: 25 Big grins
    edited January 31, 2007
    rutt wrote:
    Hey, man, shoot. I remember that I had to do something like that for this quiz as well. That chapter 1 quiz, on the other hand, well you have to get your head screwed on real tight.
    = = = = = = =

    First about LAB.

    Colors in the "a" channel go from solid green (very -) to neutral (white,grey,black) to solid magenta (very +).

    Colors in the "b" channel go from solid blue (very -) to neutral (white,grey,black) to solid yellow (very +).

    If you select a part of the photo that has a very neutral portion, it doesn't matter how you interchange the channels with each other. The result will always be neutral. Think about that for a second.

    That's because each channel is 0 (zero) or very close to it and when you interchange or invert it still remains at 0 or close to it.

    Therefore, since neutral gives you so many posibilities, that's of no value to you in determing the solution to the quiz.

    On the other hand, if you look for a portion of the original image that is very solid green, magenta (I try to leave this out since I'm never sure what solid magenta is), blue or yellow, what you now know is that the other channel will be 0 (zero) or close to it.

    For example, if part of the image is solid green, then the the "a" channel will be very - and the "b" channel will be 0 or close to it.

    That means if the "b" channel or inverse of the "b" channel is used for the "a" and "b" channels, that part of the image will become neutral or 0.

    Let's get practical. If part of the image is solid green to start and become neutral (white, grey or black) then you know that the original "b" channel
    or it's inverse must have been used for both channels. That's because neutral in the original "b" becomes neutral in both channels. Even when inverted.

    If however, the area that was originally green becomes blue, then you know the "a" channel was moved to the "b" (not inverted) and the "b" was moved to the "a" (regular or inverted).

    Likewise, if the area that was originally solid green becomes solid yellow, then the "a" channel was moved to the "b" and inverted and the "b" was moved to the "a" (regular or inverted).

    By selecting one other original area of interest (solid blue or solid yellow) you can nail down any variables such as when a channel could be moved regular or inverted.

    One other thing I used. Cyan is green/blue and violet is magenta/blue. I used this somewhat when the result was cyan or violet.

    Dan used another trick which I called "cheating" and I tried not to use it.
    He kept track of the combinations used and immediately eliminated those as a future possibility.

    As you get closer to the end that really makes it go faster since there can only be 4 combinations of each set of channels. If three are already used, you don't have to worry about inverted channels.

    I learned the above just after I started the quiz. I would have thought I'd know this after reading the LAB book.

    I hope this helps.
  • dandilldandill Registered Users Posts: 102 Major grins
    edited February 1, 2007
    Myer wrote:
    I hope this helps.
    For sure! Your post goes into my copy of the book. Thanks very much.
    Dan Dill

    "It is a magical time. I am reluctant to leave. Yet the shooting becomes more difficult, the path back grows black as it is without this last light. I don't do it anymore unless my husband is with me, as I am still afraid of the dark, smile.

    This was truly last light, my legs were tired, my husband could no longer read and was anxious to leave, but the magic and I, we lingered........"
    Ginger Jones
  • SystemSystem Registered Users Posts: 8,186 moderator
    edited February 1, 2007
    thanks myer-

    hope to check it out this weekend-

    although it makes my head spin-
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