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Thread: Understanding White Balance article

  1. #1

    Understanding White Balance article

    http://www.cambridgeincolour.com/tut...te-balance.htm

    "Performing a white balance with a raw file is quick and easy. You can either adjust the temperature and green-magenta sliders until color casts are removed, or you can simply click on a neutral reference within the image (see next section). Even if only one of your photos contains a neutral reference, you can click on it and then use the resulting WB settings for the remainder of your photos (assuming the same lighting)."

    A seagull on the water was as the "neutral reference" in the preceding paragraph. Not sure how to do this. This refers to isolating the neutral object? You need to get it in the full frame, right? (The seagull is very small in the photo.)

    And I don't understand what is being referred to in the following: "Common household neutral references are the underside of a lid to a coffee or pringles container. These are both inexpensive and reasonably accurate." What color(s) is he talking about under the lids?

  2. #2

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    Re: Understanding White Balance article

    Think of a white sheet of paper for a moment. If I shine a red light on that paper, the paper will appear red - if I shine a blue light on it, it will appear blue. In other words, the colour of objects is affected by the colour of the light that falls on it.

    So - if we have an object that we KNOW is actually one colour - but when we measure it we can see how far out it is - then the difference can only be due to the light that's falling on it - and thus we can compute the correction required to counter-act it.

    As an example -- we take a photo of a person holding a piece of paper - inside - illuminated with tungsten lights. When we measure the the colour of the paper as it appears in the photo we might find the red channel has a value of 250 - the green channel a value of 240 - and the blue channel a value of 230 - so it has a red cast to it due to the temperature of the lights. Since we know the paper is really white - when we click on it with a white balancing tool we are saying to the software "this should be neutral so adjust the entire image until this bit I'm clicking on IS neutral" - and in the case of the above it would probably reduce the red channel by 10 and increase the blue channel by 10.

    So no - the reference doesn't need to fill the frame.

    All that's really needed is a reference with no colour (so it's only a shade of gray) Common examples (that are usually close enough) are white paper - gray hair (don't ask me how I know this!) - white paint etc

  3. #3

    Re: Understanding White Balance article

    So just shoot something grey in the room (no matter what size) to set the white balance? I thought the reference (ie. a card) had to fill the whole frame. (The seagull in the article photo only takes up like 1/100 of the photo and it was used as the reference.) The article references the white seagull and says "click on that" (which I'm not sure what is meant by that). Thanks.

    Understanding White Balance article
    Last edited by ifsixwasni9e; 30th October 2012 at 01:37 AM. Reason: add

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    Re: Understanding White Balance article

    Quote Originally Posted by ifsixwasni9e View Post
    So just shoot something grey in the room (no matter what size) to set the white balance? I thought the reference (ie. a card) had to fill the whole frame. (The seagull in the article photo only takes up like 1/100 of the photo and it was used as the reference.) The article references the white seagull and says "click on that" (which I'm not sure what is meant by that). Thanks.

    Understanding White Balance article
    It depends on how you want to approach it. If you want to correct your white balance during post-production then you only need a small spectrally neutral portion in an image, but if you want to set a custom white balance in-camera then yes you'd need it to pretty much fill the screen.

    My suggestion is to adjust in in post-production, for a number of reasons.

    PS: When they say "click on that" they'll be meaning "click on it with the white balance adjustment tool"

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    Re: Understanding White Balance article

    If you'd like more specific help you could tell us what post processing software you are actually using, if any.

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