Using grey card to set color temp in camera

Discussion in 'Digital Cameras' started by Chuck Bollinger, Dec 19, 2003.

  1. My Olympus C2500 has a way to set color temperature before taking a picture by
    focussing on a white card in the scene and pushing a button. But recently I
    received the impression that I'm supposed to be using an 18% gray card. When I
    try both ways sometimes the one (white card) will look 'better' than the other
    (gray card), and sometimes the other way around.

    'Better' doesn't necessarily mean 'accurate' - just more pleasing. I can live
    with that, but occasionally I have to try to attain accuracy regardless of what
    my preference might be.

    I'll appreciate some guidance. Thanks.
     
    Chuck Bollinger, Dec 19, 2003
    #1
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  2. Chuck Bollinger

    Don Coon Guest

    I've come to the unscientific conclusion that it doesn't matter. A
    gray-scale (all RGB numbers equal) card that reflects a reasonable amount of
    light seems to work. In other words, a black card won't work --- but I
    haven't really tries it yet. What white balance seems to be is
    equalization of the RGB levels. If a component is out of equalibrium with
    the other two, the camera compensates accordingly.
     
    Don Coon, Dec 20, 2003
    #2
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  3. Chuck Bollinger

    mcgyverjones Guest

    It really should not matter. Both should be reflecting light back at the
    camera without adding any colour. The grey card just reflects less, exactly
    like using a white card with less light. I tend to use a white card indoors
    or in low light situations and a grey in bright sun.
    Of course it is easier to find reasonably accurate white material (paper
    etc) when a card is not at hand.
    Perhaps the difference you've noticed is a result of slight inaccuracy of
    your card?

    MJ
     
    mcgyverjones, Dec 20, 2003
    #3
  4. My understanding is that an 18% gray card is used for meter readings for
    reflectance -- that is, it should give you a more accurate exposure. Are
    you confusing taking a reading for exposure with taking a reading for white
    balance?
    This would be the equivalent of choosing to use a film known for warmer
    colors or for exaggerated colors (like Velvia) or for accurage colors in
    certain situations. It may be that you are getting less accurate but more
    pleasing colors with the gray card. If you want accuracy, try both and see
    if you can tell the difference.
     
    Phil Stripling, Dec 20, 2003
    #4
  5. That makes sense. I hadn't thought of the fact that both white and 18% gray
    have that balance.
    No. I'm using a photographer's gray card, white on one side and 18% gray on the
    other. And my perception of the slight difference could be psychological, as
    when someone might have one taste the two samples of the same potion and ask "Do
    you pick up basil in that one?" The suggestion may be all.

    Thanks,
     
    Chuck Bollinger, Dec 20, 2003
    #5
  6. Yes, absolutely true.
    Whether it works equally well for digital depends on the printing doesn't
    it? Using it for color balance appears to me to be different than using a
    grey card in a scene to get the correct filter pack for printing a
    negative. In any case, if the digital image can be printed showing the gray
    card accurately, I'm sure the image would be 'accurate' in its color
    rendition.
     
    Phil Stripling, Dec 20, 2003
    #6
  7. Chuck Bollinger

    DHB Guest

    Lots of good replies but I would just like to stress 1 point that
    another person pointed out.

    White or Gray is not as important to a digital camera as these 2
    factors:

    <1> The card must reflect "all" colors equally.

    <2> The card must not be overexposed.

    For all practical purposes with regard to setting a custom white balance
    on a digital camera a white card works fine as long as it covers 2/3 or more
    of the frame & is not overexposed. In direct sunlight the white card could
    easily be overexposed where as this is much less likely with an 18% gray
    card. Most cameras that allow setting a custom white balance also have a
    histogram feature. Use the histogram to make sure your not clipping the
    white "over exposed".

    In short as was already stated use the white side of your card in low
    light situations & the gray side if needed in very bright lighting.

    AWB does not work very well on my Canon Digital Rebel / 300D so I have 2
    choices, use the custom white balance feature or shoot in RAW mode & adjust
    it later. For me, RAW mode is the way to go if it's a very important shot
    or session that I might need to crop heavily or make a large print of. The
    obvious disadvantage is that it uses about twice the space on a memory flash
    card to store a RAW mode picture, I can live with that!

    Respectfully, DHB
     
    DHB, Dec 20, 2003
    #7
  8. Thank you for your reply. What is "RAW" mode? Is that a term or initials, like
    AWB for auto white balance. I think you are providing me with a technique,
    here. And when you tell me I'll probably give myself a dope slap for forgetting.

    Chuck
     
    Chuck Bollinger, Dec 20, 2003
    #8
  9. Chuck Bollinger

    Don Coon Guest

    SNIP

    Just what it says. Raw, unprocessed image files. The camera stores exactly
    what the sensors record (compressed on Canon DSLRs) along with the original
    settings which are used as defaults by computer-based conversion programs.
    Obviously pre-shot variable such as shutter speed and f-stop cannot be
    modified in post processing. But parameters such as white-balance, contrast,
    saturation, sharpening, brightness and color-tone can. Note: this is the 50
    cent explanation : )
     
    Don Coon, Dec 20, 2003
    #9
  10. Chuck Bollinger

    DHB Guest

    "RAW" is basically a way of recording the image DATA from the CCD
    without applying in-camera processing. It's like selecting a "jpg" or
    "TIFF" mode. Check your cameras manual to see if it offers this feature.

    The 3 big advantages in recording your image in "RAW" mode is that
    "Color Temperature", "Sharpening" "Saturation" are not done in camera & thus
    you can do them when you covert the RAW image DATA to it's final format for
    printing or sharing.

    To be honest, I am still in the learning curve with RAW mode but the
    flexibility it offers to tweak things without image degradation is worth the
    extra effort & flash memory space it uses.

    Some additional info. here but I am sure you can find much better
    information & explanation of RAW image DATA & processing via a Google
    search:

    http://www.steves-digicams.com/2003_reviews/300d_software2.html

    As you can tell, I am still learning about digital photography also &
    hopefully that will continue for as long as I can hold a camera!

    Respectfully, DHB
     
    DHB, Dec 20, 2003
    #10
  11. Chuck Bollinger

    DHB Guest

    Chuck Bollinger,
    your "50 cent explanation :" just blow away my 2
    cents worth!

    Thanks for the assist.

    Respectfully, DHB
     
    DHB, Dec 20, 2003
    #11
  12. Chuck Bollinger

    DHB Guest

    Don Coon,
    sorry I copied the wrong name, it's just been 1 of those
    days. Thanks again for the 50 cent explanation though I think it was worth
    much more than that.

    Respectfully, DHB
     
    DHB, Dec 20, 2003
    #12
  13. RAW mode is an image format - and at the bottom of the menu in
    the creative zone (manual settings).

    It stores the raw data that comes off the chip, rather than storing
    a processed image. That means no white balance has been applied to
    the stored images. That has to be done on the computer.

    Another advantage is, that the RAW image has 12 bit color values
    for the pixels. RGB = 36 bit color rather than the 3x8bit = 24
    bit of JPEG. So you can actually save some of the highlights
    that has been burnt away in the conversion program.

    So there are lots of advantages to RAW mode. But the disadvantages
    are 2-3x the storage + you need to do manual processing.
     
    Povl H. Pedersen, Dec 20, 2003
    #13
  14. Chuck Bollinger

    stan Guest

    Depends on the light in the area where you're shooting. You simply need to
    experiment Don't confine yourself to just the grey and white cards for
    adjusting your camera's white balance setting. It also depends on the
    effect you want to achieve with a given photo. You can also try non-white
    cards, even such things as a bright red card, green, whatever just to
    see how things turn out.
     
    stan, Dec 21, 2003
    #14
  15. Chuck Bollinger

    Don Coon Guest

    A common use of something different is to use a very slightly blue tinted
    "white card" to get the effects of a warming filter. However, I find it's
    easier to use post processing filters as in PS CS to get the same result.
     
    Don Coon, Dec 21, 2003
    #15
  16. Chuck Bollinger

    Peter Aitken Guest

    In theory a white or gray card will work equally well. The idea is that for
    either the RGB values should be equal so if there is a color imbalance the
    camera can detect and correct for it. A white card however has the potential
    problem that it may be too bright and saturate the sensor. Its RGB "value"
    may be 300, 350, 400 but since the camera image can detect values up to 255
    only this will come thru as 255,255,255 and appear to be perfectly balanced.
     
    Peter Aitken, Dec 22, 2003
    #16
  17. OK, good. That goes along with a previous poster who mentioned using white in
    lower light and gray in bright situations. That sounds like a good practice.

    My 'perception' of difference has to have been bogus. I'm convinced now and
    chastened, like in the old cliche movies where someone becoming unhinged gets
    slapped and says, "Thanks. I needed that."

    Thank you.
     
    Chuck Bollinger, Dec 22, 2003
    #17
  18. In theory a white or gray card will work equally well. The idea is that
    for
    balanced.

    But if you avoid the saturation by choosing the appropriate exposure when
    measuring white balance, might not a white card may have a better chance
    of being spectrally flat than a grey card?

    David
     
    David J Taylor, Dec 22, 2003
    #18
  19. Chuck Bollinger

    Ender W. Guest

    Most modern cameras exposure meters are calibrated to ANSI standards
    which translates to about 12% gray. National Geographic says that
    studies have shown that an average scene really reflects 13% instead
    of 18%, but cards still use 18% for consistency.Using an 18% gray card
    for exposure will give you about a half stop under exposure. The best
    thing to do is to use a gray card to set exposure and a white card for
    white balance.Remember that the 18% gray or 90% white card will only
    be correct when it is exposed properly.Shoot frames of your gray and
    white cards and measure their color values in Photoshop or something
    similar. IF you want to do it the easy way, check out the Wallace
    ExpoDisc.(Not affiliated but I own one.) I think that they are 10% off
    till the end of the year.----------Greg---------------------
     
    Ender W., Dec 25, 2003
    #19
  20. Chuck Bollinger

    Ender W. Guest

     
    Ender W., Dec 25, 2003
    #20
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