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Old 19th of February 2005 (Sat)   #1
PhotosGuy
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Default Gray Card…White Paper. What’s best?

This is a continuation of the post, “Gray card: Why your meter may be lying to you!” at:
http://photography-on-the.net/forum/...ad.php?t=54281
I’m putting it in a separate thread ‘cause the pic is 100K.

There’s a lot of talk about what’s best for exposure, Gray cards, white paper, expensive attachments for the lens. I hope to put that to rest here. Draw your own conclusions, but a plain piece of paper does it for me.

The white 'card-paper' has an advantage in low light situations which is explained in the data sheet that came with my card - it's easier to get a reading since it is brighter.

Take a reading of the white card/paper. Center the meter & take a picture at that setting. You'll see the histogram is concentrated in the middle - just where you want it. Use that shot to set your WB.

For the exposure setting, open up ABOUT 2-1/3 stops & take another shot. Chimp the exposure so it almost touches the right side & set it in Manual mode. Done in less than a minute.
That might seem like a lot to do to get the exposure, & it is, but we can simplify the process. There's an example of using your hand instead of white paper for exposure in this thread: Need an exposure crutch?

NOTE: Make sure that you haven't included ANY reflective highlights in the pic (Sky, chrome, etc.). They WILL throw off the exposure!
(Unless it's the sky that you want "properly" exposed, that is!
More on how the subject affects the exposure in Post # 47

------------------------
EDIT: Jon made a comment in another thread that has some merit, so I'm adding it here:
"For instance, many papers contain UV brighteners, so that neutral white paper you selected by comparison with three other sheets of paper under your desk lamp (2900 K) will almost fluoresce when you bring it out into a strong UV source, like a sunny day, thus giving a strong colour imbalance. That's why using a commercial, neutral, grey card is preferable. In fact, it's what Canon is currently recommending."

That's true. Still, I rely on RAW & RSE to make final adjustments to the WB on post-processing, so I ignore that excellent advice!
I still use cheap, bulk, printer paper most of the time. I always have it with me to take notes on. Quartz lighting indoors shouldn't cause any UV fluorescing, and the cam has a UV filter, but I'll run some tests with a Kodak white card vs. the brand of white paper & the lighting I'm using at the time (flash or daylight). Maybe you should, too.

Re-edit: Here they are:
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File Type: jpg Gray-card_White-paper.jpg (100.0 KB, 9136 views)
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Last edited by PhotosGuy : 20th of July 2012 (Fri) at 00:16. Reason: typo
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Old 19th of February 2005 (Sat)   #2
Tom W
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Default Re: Gray Card…White Paper. What’s best?

Well, they're within 1/3 stop of each other. How did your gray card exposure show on the histogram? Right in the middle?
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Old 8th of March 2005 (Tue)   #3
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Default Re: Gray Card…White Paper. What’s best?

Quote:
How did your gray card exposure show on the histogram? Right in the middle?
Sorry for the wait, Tom. I didn't get an email notification that there was a reply to the post.
Here's a pic of a selection of the top pic in Levels.
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File Type: jpg GrayCardHistogram.jpg (37.0 KB, 8840 views)
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Old 8th of April 2005 (Fri)   #4
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Default Re: Gray Card…White Paper. What’s best?

I was going to post a question that is related to this thread so I decided to reactivate it instead. But I’m not sure it its still alive. I have the same question as Tom W, but I think the question is slightly more complex than the answer given. I have an old G2 which I think is slipping out of calibration but in order to test it to know for sure I am confronted with a dilemma. I need a relative measure in order to know if the grey card exposure is right. For example, RGB 128 comes to mind, as does 50%, but there are two problems with using levels and percentages as a relative measure, firstly, they are not colours or densities they are simply digitised control signals which represent different colours and densities in different spaces. Lab luminosity values ( L*) are the only indication of true density or colour. For example 50% in a greyscale 2.2 space is L*54, but 50% in a 1.8 greyscale space is L*64 and 50% in a 10% dot gain space is L*70, and the same is true for RGB 127. The second problem with using levels or percentages and reading them in Photoshop is tracking the profile tags and conversions from the point of exposure to the moment it arrives in Photoshop. What Photoshop displays in the info pallet will depend entirely upon how the colour settings box has been configured and whether the file has traveled through an input profile or arrived directly untagged into the RGB workspace. I wont even mention the further complication of shooting in raw and having to travel through gamma encoding and raw conversion settings that will drastically change where the data ends up. I think the question being asked here was, where did the reflective luminance from the grey card show up on the in-camera histogram (not after being brought into Photoshop) when the grey card exposure was correct

The question I would like to add is…

When testing for the correct grey card exposure in Photoshop, after noting the specific conditions of its passage (lets say in jpeg to remove the raw conversion variable), what luminosity value are we looking for middle grey? Is it L*54 in a 2.2 space and L*61 in a 1.8 space? . The reason I ask is because after determining the correct exposure of a Kodak Q14 greyscale target based on the first apparition of the line between the absolute white patch and the patch next to it while maintaining pure white L*100, this exposure produces a completely different L* value for the Kodak 18% Grey card. I am even beginning to wonder if there isn’t another grey card for digital capture, one that would be a higher grey value.
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Old 8th of April 2005 (Fri)   #5
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Default Re: Gray Card…White Paper. What’s best?

Quote:
but I think the question is slightly more complex than the answer given.
It very probably is! I'm no expert on that sort of thing, I shoot RAW 99.999% of the time, & my major concern is to get close enough to fix it in PS. Also, in my case, it would be usless measurebating since the gray card I use is about 40 years old & a bit banged up! Sort of like me.
I did shoot a small jpg using a 105mm way out of focus to try to minimize variations & drew what the LCD histogram looked like against the gray card background & included the PS histogram as a reference. I hope that it helps you out in some way. Feel free to start your own thread & reference this one. If you do, please post a link here to help other people out, too.
Thanks,
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Old 4th of May 2005 (Wed)   #6
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Default Re: Gray Card…White Paper. What’s best?

Quote:
Draw your own conclusions, but a plain piece of paper does it for me.
To summarize & just to make everything perfectly clear, I don't carry a gray card anymore as it's too big & I get the same results by using a sheet of white paper in Manual mode & chimping the exposure to the right as shown in the first example.
As long as the white paper is reflecting light from the source, AND you haven't included ANY reflective highlights in the pic (Sky, chrome, etc.), you're going to get the same effect as using an incident meter, except that you have to remember to open the lens up 7-8 clicks afterward. Without carrying a meter & extra batteries, or wondering where the &^$#@ the little piece of plastic you use for WB is hiding this time!

I use the darker "on-the-meter" exposure for the Custom WB, as the cam needs an exposure with some "gray" pixels in it to compute the WB. Underexposed white paper will provide the gray needed for that.

I feel that individual variations in the color of the white paper are insignificant, unless you insist on shooting JPGs, (in which case I have to wonder why you're pi**ing away the money you spent for an expensive cam & lens!). First because the variations are so small, & second because I shoot RAW 99.999% of the time.

EDIT: Don’t have a gray or white card, or hand held meter with you? “Film tricks” can help you out.
Need an exposure crutch?

Good luck & have fun!
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Have you thought about making your own book? // Need an exposure crutch?

New Image Size Limits: Image must not exceed 1280 pixels on any side.

Last edited by PhotosGuy : 31st of August 2006 (Thu) at 12:09.
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Old 2nd of April 2006 (Sun)   #7
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Default Re: Gray Card…White Paper. What’s best?

PhotosGuy, I use automatic exposure on a white sheet of paper for White Balance ... I shoot jpegs 99.999% of the time ... far superior to AWB ... but it sounds like you are suggesting that some other exposure method would be superior, eh? Oh, I spent all that money because the damn camera does what I want ... RAW is not the be all and end all in life!
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Old 3rd of April 2006 (Mon)   #8
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Default Re: Gray Card…White Paper. What’s best?

Dwight, do what works best for you & the things that you shoot.
I shoot a lot of cars in low light & the chrome reflections throw the meter off + as I said above, "The white 'card-paper' has an advantage in low light situations which is explained in the data sheet that came with my card - it's easier to get a reading since it is brighter."
Quote:
RAW is not the be all and end all in life!
True, but Why I love RAW - '53 Ford Sunliner is why I'll stick with it. I'm used to having the equivalent of a "negative" to work with.
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Old 9th of April 2006 (Sun)   #9
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Default Re: Gray Card…White Paper. What’s best?

Quote:
Originally Posted by DwightMcCann
RAW is not the be all and end all in life!
I checked around and it IS.
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Old 9th of April 2006 (Sun)   #10
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Default Re: Gray Card…White Paper. What’s best?

Sorry, Mike, although I know this is the first time EVER, you have checked the wrong references and have gotten bad information. "Drugs, sex and rock 'n roll" are the be all and end all of life, even though I have little experience with any!
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Old 28th of May 2006 (Sun)   #11
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Default Re: Gray Card…White Paper. What’s best?

I buoght my camara used and owner said it the AWB was reset by Canon and I have had no promblems with white color balnance at all. I photoed wedding for other company two month ago and had to use a photodisk from HK. I did not see any difference between the custome setting with disk and the auto white balance.

I have a little more luck with weddings here how ever. Brides they wear almost anything except white here in China. Red, blue, orange.

But some do wear white. So my AWB works same as custome with photodisk.
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Old 20th of February 2008 (Wed)   #12
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Default Re: Gray Card…White Paper. What’s best?

Quote:
I did not see any difference between the custome setting with disk and the auto white balance.
In my test with incandescent light, I see a lot!
Notice that the very last exposure in the 2nd group of tests was of a gray card. This thread has a good illustration of target influenced differences in exposure readings, too.
http://photography-on-the.net/forum/...ad.php?t=54281
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Old 20th of February 2008 (Wed)   #13
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Default Re: Gray Card…White Paper. What’s best?

I think this thread gets some kind of award for being slowest. There are new posts every year or two.
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Old 14th of March 2008 (Fri)   #14
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Default Re: Gray Card…White Paper. What’s best?

So correct me if I'm wrong. From what I understand:

In manual mode,

>Place a white card/sheet so that the light source that lights your subject is hitting it.

> Fill the frame with it, or spotmeter off of it.

>now what? Expose about 1 1/3 stops to the right? 1 stop? No stops? This is the part I don't get.
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Old 14th of March 2008 (Fri)   #15
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Default Re: Gray Card…White Paper. What’s best?

Quote:
Expose about 1 1/3 stops to the right?
That's about right. (This question refers to the link in post #6.)

You just want to get the white peak in the histogram almost touching the right edge of the histogram so whites won't be blown out. Everything else will fall into place IF it's a "normal" shot.
If there aren't any whites in the shot & it's made up of predominantly medium/dark tones, then the Expose to the right method would be best.
Quote:
> Fill the frame with it, or spotmeter off of it.
IF there aren't any bright, reflective areas in the shot like chrome or sky, you don't need to fill the frame or spot meter the white.

Got it?
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