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Thread started 04 Mar 2010 (Thursday) 00:24
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7D and WB calibration with 18% gray card

 
roakey
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Mar 04, 2010 00:24 |  #1

On page 71 of the 7D instruction manual there’s a description on how to set a custom white balance using a white card. On the next page, it states that an 18% gray card can be used to produce a more accurate WB setting.

What it doesn’t say is how you tell the camera that you’re setting the WB with an 18% gray card versus a white card.

I haven’t been in that part of the camera menu yet, so maybe there’s an obvious way to tell the camera that you’re using a gray card? If not, how does how to set the WB if it doesn’t know what the calibration “target” is?

Roak


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Redaddiction
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Mar 04, 2010 00:52 |  #2

It just meters off white or the gray card. If you go through the settings you can take a picture of the white card or gray card then use that as your custom wb. I haven't used it yet in a tricky lighting situation but hope to save some time pp.


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Redaddiction
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Mar 04, 2010 00:52 |  #3

Sorry just to make it clear it does NOT give you a choice on white card or gray card.


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gdl357
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Mar 04, 2010 01:08 |  #4

I use a Whibal card which is grey but is a WHITE BALANCE REFERENCE CARD. I do it on purpose to shoot with Fleurescent light setting in whitebalance. I take a picture of the card in the same lighting she is in and then I take a few test pictures of my wife.

I go to my computer and load them in DPP. the pictures are all purple/blue if I remember. I click on the Whibal card picture (which is the first pic of every scenario I am in and choose the SHOT SETTING to CLICK WHITE BALANCE. I take the dropper and click on the blue card and boom they all get autocorrected and skintones are spot on!

I have the camera in auto WB and take a picture of the card while my wife holds it (or you can hold it yourself or throw it on the floor) I take a pic of the card in every situation I am in that has a different light source so I will have a pic or the card for every place I took pictures that day, ready to be edited in DPP for perfect WB.

You can take a picture of the card and put that picture in the custom white balance but then you will have to do this every time the light changes, and you will end up shooting with the wrong card picture because you will forget to change it in camera custom settings. It's harder this way and more time consuming if your going from outdoors to indors and outdoors again.

http://www.whibalhost.​com …ials/WhiBal/01/​index.html (external link)


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tzalman
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Mar 04, 2010 06:54 |  #5

White and neutral grey are the same color. Neutral grey is any color whose RGB values are equal. Medium grey is 128/128/128, white is 255/255/255. A custom white balance can be made from any shade of grey as long as it is truly neutral. The camera or RAW converter examines the RGB values and calculates the correction needed to make the R and the B equal to the G.

Also, when you shoot the white paper the camera will make it grey unless you use EC to increase exposure. From the camera's point of view there is no difference between an image of a white card without EC and the image of a grey card, so it doesn't need to be told what shade the card is.


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SkipD
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Mar 04, 2010 07:02 |  #6

The problem with trying to use "white paper" as a neutral color reference is that ordinary white paper is not necessarily truly neutral. It is far better to use a product which is guaranteed to be neutral.

A neutral gray card (such as the WhiBal product, for example) is far more versatile than a white neutral reference card. Why? It's because it can be used for both a reference in setting up a "custom white balance" in the camera and it can be used as a reference in the scene. If you put a white card in the scene as a reference, it could be very easily overexposed, blowing out at least one color channel and thus becoming essentially useless.

Since I always shoot in RAW mode when the color of my images is important (which, for me, is all the time), I merely place a WhiBal card (or any other calibrated neutral gray card) into the scene for a test shot. Then, during RAW conversion (a post-processing step), I use an "eyedropper" tool to sample the gray card in the test image. The resulting color temperature and tint numbers are then transferred into the RAW conversion of the rest of the images in the series (in a single batch conversion of the rest).


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umphotography
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Mar 04, 2010 08:00 as a reply to  @ SkipD's post |  #7

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roakey
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Mar 04, 2010 08:21 |  #8

tzalman wrote in post #9726375 (external link)
Also, when you shoot the white paper the camera will make it grey...

Thanks folks, this is basically the answer I was looking for, as I slap my forehead. To oversimplify, the exposure will adjust the white card to 18% gray, or leave the 18% gray card alone, so they amount to the same thing (as long as they're truly "pure" white or "pure" gray).

Same reson you underexpose on snow if you fail to compensate...

Though the exposure in such a case isn't all that important, it's the spectrum.

Thanks!

Roak

Ps. I already have [too many] cards. :)


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artyman
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Mar 04, 2010 10:53 |  #9

I have a selection of white watercolour papers, and they are all different, so white isn't neccessarily white. ;)


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Pearlallica
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Mar 04, 2010 11:01 |  #10

i tried one of those expo discs that you place infront of the lens. Bit waste of money. I sold it for the same value I bought for on eBay. I guess there are a lot of suckers out there that have faith in these type of accessories. Obviously - I was one of them. I got much better results from a 4 dollar grey card from B&H. Use it all the time with my 7D under harsh tungsten lighting. Works like a charm! Just hold the card directly under light source, turn off auto focus, (use auto WB setting) take the shot and select the image as your custom white bal reference.

I've shot home videos and never thought to use the grey card for video too. Some of my videos turn out very saturated in yellow/orange because i use tungsten bulbs. I now remember to use the grey card for video as well.


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umphotography
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Mar 04, 2010 11:40 |  #11

Pearlallica wrote in post #9727671 (external link)
i tried one of those expo discs that you place infront of the lens. Bit waste of money. I sold it for the same value I bought for on eBay. I guess there are a lot of suckers out there that have faith in these type of accessories. Obviously - I was one of them. I got much better results from a 4 dollar grey card from B&H. Use it all the time with my 7D under harsh tungsten lighting. Works like a charm! Just hold the card directly under light source, turn off auto focus, (use auto WB setting) take the shot and select the image as your custom white bal reference.

I've shot home videos and never thought to use the grey card for video too. Some of my videos turn out very saturated in yellow/orange because i use tungsten bulbs. I now remember to use the grey card for video as well.

thats all good, but the thing about the photovision type discs is that not only does it set the white balance properly, but, you know exactly where your exposure is and if its right or wrong. you now have the ability to push it a little right w/o clipping your highlights.....thats huge. you know exactly where your at. now that ive used them and understand them, i wont shoot w/o them. you really cant miss and if you use your lightmeter to measure your manual flash output, you definately cant miss.


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SkipD
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Mar 04, 2010 12:28 |  #12

slowdad wrote in post #9727919 (external link)
thats all good, but the thing about the photovision type discs is that not only does it set the white balance properly, but, you know exactly where your exposure is and if its right or wrong. you now have the ability to push it a little right w/o clipping your highlights.....thats huge. you know exactly where your at. now that ive used them and understand them, i wont shoot w/o them. you really cant miss and if you use your lightmeter to measure your manual flash output, you definately cant miss.

How is it possible to use an Expodisc (or any of its clones) for exposure control? I've never heard of anyone doing that before.

In my opinion, the Expodisc is a rather clumsy way to deal with color control as well when compared with the conventional neutral gray card.


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umphotography
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Mar 04, 2010 15:23 |  #13

SkipD wrote in post #9728263 (external link)
How is it possible to use an Expodisc (or any of its clones) for exposure control? I've never heard of anyone doing that before.

In my opinion, the Expodisc is a rather clumsy way to deal with color control as well when compared with the conventional neutral gray card.

use your histogram. the black/white/grey show up as lines. you keep it right in the middleand keep you highlights and shadows off the edges. to far to the shadow side or highlight side you adjust the f/stop setting.


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Mar 04, 2010 15:46 |  #14

SkipD wrote in post #9728263 (external link)
How is it possible to use an Expodisc (or any of its clones) for exposure control? I've never heard of anyone doing that before.

The Expodisc had its start in the film days, for exposure! They had to re-invent themselves for digital, to be used for WB.

The Koday gray card, the PhotoVision, and the Douglas Gray Card can all be used for both exposure setting and for WB. In if the squares were larger on the Colorchecker, the fourth box on the bottom row could be, too.


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Mar 04, 2010 16:21 |  #15

slowdad wrote in post #9729427 (external link)
use your histogram. the black/white/grey show up as lines. you keep it right in the middleand keep you highlights and shadows off the edges. to far to the shadow side or highlight side you adjust the f/stop setting.

Where do you point the camera with the Expodisc on it for this? Where is the camera during this relative to where you'd make the image from? I ask this because for white balance, you're supposed to aim the rig at the light source(s).


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7D and WB calibration with 18% gray card
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