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Old 28th of June 2004 (Mon)   #1
Mark0159
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Default How to make your own gray scale card

Hi

I remember a long time ago someone was asking on how to make there own gray scale card. So they can have the correct colour of white when shooting in lighting that might not be ideal.

As some of you may already know that a gray card is 15% gray. I started thinking about this the other day and I believe that I have found a way of making a gray card at home.

please check it out and let me know what you think.

http://homepages.ihug.co.nz/~markpc/wb/wb.htm

If you wont to test it out yourself, I have provided info on the steps that I used.

and I believe my boss does not read this forum
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Old 28th of June 2004 (Mon)   #2
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yes, Mark, i do read this forum. please see me in my office tomorrow morning... just kidding...

i've not ever used a grey card for white balance - i've always used them for proper exposure, but i guess it's from old-skool thinking. btw they're great for snowy scenes that tend to blow out in the bright sun (btw you can use the palm of your hand in a pinch...)

now i know there are expo-discs and pringles tops and a few here have reported great results. judging from your photos it works pretty well. im sure a lot of other will use the 'i shoot raw...' response - in any event it would be great to see some real world shots.
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Old 28th of June 2004 (Mon)   #3
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Just one minor quibble - standard grey cards are 18% (setting would be 209, not 217). Shouldn't affect colour balance much, but it has the potential to skew your exposure if you use it for metering.

The difference you saw between the plain paper and your grey card was probably due to the paper not being a "pure" white. Composition of the stock, or the brightening chemicals used, may have caused this. When you overprinted, you got straight black toner masking out the background. BTW, Kodak's 18% grey card flips to a 90% white (pigmented) card.
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Old 28th of June 2004 (Mon)   #4
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I may be wrong, but isn't a gray card with 18% reflectance the same as middle-gray, Zone V, 128R-128G-128B ? I don't think you can translate the 18% directly to the linear 0-255, since 209-209-209 is not middle gray. Nothing wrong with using that for white balance, though, as long as it's neutral. Again, I could be wrong ...
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Old 28th of June 2004 (Mon)   #5
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A cheap grey card is about $5. An expensive one is $15.

If you're going to make your own, you need to ensure that you've got all your bases covered in terms of printer calibration, to be sure your printer is creating a neutral card. I'd trust the commercial guys to get this right before I do, at least if I'm constrained to putting in less than $5 worth of effort into it.
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Old 28th of June 2004 (Mon)   #6
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A TRUE "Gray Card" can be used for 2 purposes: 1/ Assist the exposure setting process - 2/ Assist the WB setting process. The exposure adjustment should be done first then an image of this gray card is used to set the custom WB.

There are a few things you should keep in mind about gray card:
- You CANNOT print a gray card using an inkjet printer. No matter how well calibrated you system is, you CANNOT achieve a 100% neutrality in the printed gray color. The color of the printed card WILL shift over time.
- A commercial gray card is NOT printed. The card itself is 100% gray throughout.
- The reflectance of the surface affects both of the EV and WB settings.
- The angle of the gray card in relation to the camera's sensor plane makes a difference.

For a home made custom WB source, use the photo paper you normally use, lustre surface preferred. Photo paper (unless it's used for BW photo and has specific Warm /Cool tone dyed in the pulp) is made to be as neutral as possible. If you do a WB off this paper, you also cancel the warm /cool shift of the paper in the process. Thus the color when printed on this particular paper, will be very accurate.

One last note, a "gray card" is not the same as a "grayscale card". A grayscale card has a "grayscale" printed on the card for the purpose of setting up the exposure. The grayscale is normally shown as B&W frames representing 10 values of gray going from a 100% black to a 100% white (or 255-level to 0-level of black). You use an "eye dropper" tool and click on the 255, 128, and 0 levels to set the black, neutral, and white point.

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Old 28th of June 2004 (Mon)   #7
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well that goes to show you how good my memory is when it comes to numbers 15% or 18% at least you can see the difference when changing the colour of white. It is also supprising to note the change when you leave the camera on custom white balance.

At the end of the day, if there is a question about the colour of white, then shoot in RAW, and change in post processing. that is one of the advantages of digital.

Just thought I would share my experment with the group and it is always good to get feed back. learn more that way.
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Old 28th of June 2004 (Mon)   #8
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Yes, thanks for sharing NZL.
It's fun to experiment with these things.
Have you tried using a coffee filter yet?

BTW, once you have set the custom WB, can that image be deleted?
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Old 28th of June 2004 (Mon)   #9
Mark0159
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I am not to sure about the coffee filter bit yet, why cause I don't have a coffee machine, and the reason I don't have one of those is because I don't drink coffee.

I am not to sure about deleting the image you have used for the WB. I would think that the once the camera has got WB from the image, it no longer requires the image.

I could be wrong however.
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Old 29th of June 2004 (Tue)   #10
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Default Keeping custom white balance images?

I keep my "standard" custom white balance reference shots on an otherwise almost useless 16 Meg flash card...

I sometimes shoot items using 3 cheap 500 watt halogen lamp stands... I've stored some of my reference white .jpg's on the little card... I shot a few different white papers with color bracketing and I can pre-tweak for a warmer or cooler look by selecting which reference image I use...

The same thing works during family gatherings, etc… If I have a moment beforehand I’ll prep a CWB for the different lighting in the areas that will be used and then use the 16 Meg or just put the reference files on the in-camera CF card or micro-drive…
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Old 29th of June 2004 (Tue)   #11
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Quote:
Originally Posted by drisley
BTW, once you have set the custom WB, can that image be deleted?
Yes, try it.
-harry
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