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Thread: 18% grey cards

  1. #1

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    18% grey cards

    Hello all,

    Just a brief question on grey cards.

    My understanding is that, say I'm shooting photos at a church. There are several sources of light : Candles, stained glass, real glass, artificial lighting, etc.

    If I want to try and find a nice balance for the WB, taking a picture of my grey card (with most of it in the frame) while in that particular area is all I have to do, right? (And set it as the custom white balance, obviously).

  2. #2

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    Re: 18% grey cards

    Hi Sean,

    "Sort of" -- technically speaking, an 18% grey card (emphasis on the 18% bit) is more for setting up the exposure, but it will work for white balancing as well. In reality any spectrally neutral (fancy word for grey) card will do the job (just be sure that you don't over-expose it if it's already pretty white)

    With regards to using it -- you can set a custom white balance off it, but thats doing it the hard way. The easy way for Photoshop users (and probably other programs as well) is to just use the WB tool ... you click on the grey card and it automatically adjusts the entire image ... you can then use the selected colour temperature and apply it to all other shots taken in the series.

    The biggest issue with the lighting your describing though is that it's from mixed sources ... you'll be trying to apply a "one size fits all" correction, and put simply, there is no one correctin that will neutralise the colour cast generated by light from a variety of sources (nor would you necessarily want to -- eg if you took a portrait of a couple enjoying a candlelight dinner, you'd expect to have yellow / warm tones).

  3. #3

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    Re: 18% grey cards

    Quote Originally Posted by Colin Southern View Post
    Hi Sean,

    "Sort of" -- technically speaking, an 18% grey card (emphasis on the 18% bit) is more for setting up the exposure, but it will work for white balancing as well. In reality any spectrally neutral (fancy word for grey) card will do the job (just be sure that you don't over-expose it if it's already pretty white)

    With regards to using it -- you can set a custom white balance off it, but thats doing it the hard way. The easy way for Photoshop users (and probably other programs as well) is to just use the WB tool ... you click on the grey card and it automatically adjusts the entire image ... you can then use the selected colour temperature and apply it to all other shots taken in the series.

    The biggest issue with the lighting your describing though is that it's from mixed sources ... you'll be trying to apply a "one size fits all" correction, and put simply, there is no one correctin that will neutralise the colour cast generated by light from a variety of sources (nor would you necessarily want to -- eg if you took a portrait of a couple enjoying a candlelight dinner, you'd expect to have yellow / warm tones).

    I see, thanks for the further insight Colin. Your tip of changing the WB / exposure in Photoshop after seems easier than making a custom WB for a new local every time.

    Thanks for the tips

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    Re: 18% grey cards

    Quote Originally Posted by Colin Southern View Post

    you can then use the selected colour temperature and apply it to all other shots taken in the series.
    Colin, is it possible to do this in photshop when pp-ing a jpeg? For this kind of WB corrections I use the curves to set the black point, the white point and the gray point. Is it possible to make a correction like that on a series of photo's of the same subject? So can I select an colour temperature with a photo with something like a WiBal (I think I'm going after that one) and than apply this on a series of JPEG photo's?

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    Re: 18% grey cards

    Quote Originally Posted by Sean View Post
    I see, thanks for the further insight Colin. Your tip of changing the WB / exposure in Photoshop after seems easier than making a custom WB for a new local every time.
    Hi Sean,

    Yes - it's a lot easier (well at least I think so anyway) - plus it has added benefit of still allowing you to guestimate WB fairly closely even if you don't have a reference card in the shot (in that often you can click on something else that's supposed to be white - eg dress - shirt - (if desperate) eye).
    Last edited by Colin Southern; 27th July 2009 at 10:08 AM.

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    Re: 18% grey cards

    Quote Originally Posted by JK6065 View Post
    Colin, is it possible to do this in photshop when pp-ing a jpeg?
    Hi Jereon,

    Yes - but it's easiest if you have CS3 or CS4 as you can open a JPEG in the RAW converter just as you would a RAW file (that's where the WB tool is).

    You can adjust WB within Photoshop itself, but I don't know what the best techniques are - I work in LAB colour a lot and I just chuck on a curves layer and then move the end points for the A and B channels as required.

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    Re: 18% grey cards

    White balancing an image in PS (I mean in pure PS, without going to ACR) is possible in RGB mode but with limitations. According to the actual implementation of WB on any RAW developer, WB can be achieved in PS RGB mode with straight curves that set a new relative gain for every channel:

    18% grey cards

    The reason for it is that even if images are not linear, the gamma curve has the property to keep any linear scaling as linear.

    The bad news is that when highlights are present in the image (e.g. white blown areas), these curves will create colour casts in them given the impossibility in PS of setting an accurate toe in the curve ending in (255,255).

    But conceptually it is possible, and it works on images without blown areas. The previous curves can white balance this deliberately wrong white balanced image:

    18% grey cards

    Into this one:

    18% grey cards

    The curves were obtained by setting the white point of the curves in the red spot, plus a previous exposure reduction curve to avoid clipping. For a tutorial with the detailed process: JPEG WHITE BALANCING IN PS. It's a nice exercise to understand the implementation of WB.

    A couple of extra samples using this technique:

    18% grey cards

    18% grey cards

    Regards.

  8. #8

    Re: 18% grey cards

    There is another way that gives you non-destructive editing and the ability to fade the amount of correction down or up to tweak...

    Sample a neutral portion of the image with the eyedropper set to 5x5 average (if there is no neutral, do a Filter->Blur->Average on the entire image and sample that) and then fill a new layer with that color. Invert (Cntrl-I) the filled layer so you now have an opposite color. Set the filled layer blending mode to Color Dodge. The color cast should be gone.

    If you'd like to tweak, create a Hue/Sat adjustment layer and clip it to the filled layer, and adjust the sliders to taste.

    Sample 1 PSD
    Sample 2 PSD
    Last edited by kevinf; 28th July 2009 at 08:02 AM.

  9. #9
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    Re: 18% grey cards

    I am fairly new to this but I recently had occasion to shoot in a church environment. Fortunately, the first thing I did before everybody showed up, was to shoot an 18% grey target in the mixed lighting on the stage where I knew most of my subjects would be when I shot them. (I should use the word "photographed" rather than "shot" shouldn't I.) In any event I did most of my photography using a flash fill so I didn't use the custom white balance for that but when I shot without the flash using the custom white balance I didn't have to tinker with the color at all. Perhaps beginners luck but I was very pleased with the custom white balance using the 18% grey target on this occasion.

    This was a 100th birthday celebration....I am not a wedding photographer.

    Chuck

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    Re: 18% grey cards

    Quote Originally Posted by CNelson View Post
    I shot without the flash using the custom white balance I didn't have to tinker with the color at all.
    Hi Chuck - custom white balances do work just fine, in fact in an environment like you were in (where the colour temperature isn't changing) it's probably the easiest technique.

    The other approach is to just include the grey card in one of the shots and then adjust later in post-processing; for some reason this seems to frighten a lot of people, but it's only a few mouse clicks in an Adobe environment - one simply opens the folder in Bridge - select all - open all in ACR - adjust the temperature with the white balance eyedropper tool - and then apply that temperature to all the other images. Probably just as quick (or even quicker) than setting a custom WB. (Not trying to knock the custom WB approach - you just have to remember to keep changing it as the lighting conditions change, whereas with the "adjust afterwards" approach you can fix it all in post processing (easiest if you have the grey card in one of the shots for each lighting type, although anything white can be used with reasonably good results).

  11. #11

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    Re: 18% grey cards

    One of the best things I have done recently, after reading a recent thread here, was to buy a Whibal 18% grey card.

    In a particular situation recently the camera on auto white balance shot at 4800, the Whibal card said 5200. Guess which skin tones looked best?

  12. #12
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    Re: 18% grey cards

    Quote Originally Posted by Colin Southern View Post
    Hi Chuck - custom white balances do work just fine, in fact in an environment like you were in (where the colour temperature isn't changing) it's probably the easiest technique.

    The other approach is to just include the grey card in one of the shots and then adjust later in post-processing; for some reason this seems to frighten a lot of people, but it's only a few mouse clicks in an Adobe environment - one simply opens the folder in Bridge - select all - open all in ACR - adjust the temperature with the white balance eyedropper tool - and then apply that temperature to all the other images. Probably just as quick (or even quicker) than setting a custom WB. (Not trying to knock the custom WB approach - you just have to remember to keep changing it as the lighting conditions change, whereas with the "adjust afterwards" approach you can fix it all in post processing (easiest if you have the grey card in one of the shots for each lighting type, although anything white can be used with reasonably good results).
    Thanks Colin...I'll have to try this.

    Chuck

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