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06-23-2011, 10:40 PM   #16
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Using white paper or a grey card makes no difference, white is a shade of grey! Just a brighter shade.

A neutral grey is any pixel where the Red, Green and Blue values are the same. White will be R=256, G=256 and B=256, a grey card will read something like R=128, G=128 and B=128 either are colour neutral.

The advantage of a grey card is you can set a perfect exposure too, by including a grey card in one of the images in a sequence you can set WB and the Gamma point precisely in post processing, or you can spot meter it. Using a grey card for exposure is taking an incident light reading, which will always be more accurate than a reflective light reading.

Chris

06-24-2011, 12:29 AM   #17
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As I wrote before: the best possible WB card is the one which offers as large input signal (i.e. as close as possible to (255,255,255) but (critically important!) without clipping any channel.

An 18% grey card is rather dim so it won't clip (advantage) but the accuracy will suffer (small signal/noise ratio). The other very important problem is this card's spectral characteristic (is it spectrally flat?) It does not have to be for exposure but it must be for WB.

The white balance card must be spectrally flat (which will yield very good result in most lighting conditions) and white enough so it won't clip while still offering a reasonably high input signal. See my other post: https://www.pentaxforums.com/forums/general-photography/131326-grey-white-balance-cards.html#post1365877

About your monitor - I cannot recommend the Bruce Frasier's "Real World Color Management" enough! Buy it, borrow it from your local library, beg for it, anything. Just read it!
06-24-2011, 04:43 AM   #18
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Thank you, ChrisJ and Howdy! Very helfpul info!
06-25-2011, 09:03 AM   #19
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QuoteOriginally posted by Laurentiu Cristofor Quote
Setting the WB later is time consuming and it also prevents reviewing images in camera - it is very hard to judge the quality of an image when WB is off.
With any reasonable software, setting wb in pp is far faster than doing it in camera. As for checking quality of pictures in camera, find that awb does a good enough job for that except in the worst kinds of stage lighting. And in those cases, there is no in camera wb adjustment that would help.

06-25-2011, 09:50 AM   #20
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QuoteOriginally posted by Marc Sabatella Quote
setting wb in pp is far faster than doing it in camera
I am very sorry Marc, but it is not always so easy. How would you set a white balance of a yellow flower on green grass, without any grey patch to obtain the WB multipliers from? (Assume that you are using the UniWB for an additional difficulty). In such a situation a good WB card is, in my view, rather necessary.
06-25-2011, 09:51 AM   #21
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I don't get the need for perfect colour accuracy. Unless you're shooting carpet samples or something like that! AWB is usually pretty neutral, and if it fails you can use a lightroom preset, or set it yourself in post processing. For me, colour that *looks* natural and works for the shot is the main objective, and I will tweak the WB to warm up or cool down the shot as I feel appropriate. Life's to short to shoot grey cards...
06-25-2011, 09:58 AM   #22
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QuoteOriginally posted by ihasa Quote
I don't get the need for perfect colour accuracy. Unless you're shooting carpet samples or something like that! AWB is usually pretty neutral, and if it fails you can use a lightroom preset, or set it yourself in post processing. For me, colour that *looks* natural and works for the shot is the main objective, and I will tweak the WB to warm up or cool down the shot as I feel appropriate. Life's to short to shoot grey cards...
I agree. I warm up a fair few of my shots as I tend to be out in the middle of the day with my daughter when the light is quite harsh. A little bit of warmth to the light makes the pictures much more pleasing.

I make more of an effort to get it right with images for my website, but even then I'm not that fussed about total accuracy. A candle shot in a room that looks all cosy and warm sells better than one shot with total colour accuracy.
06-25-2011, 10:03 AM   #23
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QuoteOriginally posted by ihasa Quote
I don't get the need for perfect colour accuracy
Me either - the perfect accuracy is super-difficult to achieve and can often produce inferior results (I tried making an ICC profile for my K7 but the result was an absolute failure).
QuoteOriginally posted by ihasa Quote
AWB is usually pretty neutral
The keyword here is: "usually"...
QuoteOriginally posted by ihasa Quote
colour that *looks* natural and works for the shot is the main objective
I cannot agree more with this. The problem is that it is not so easy to find a good white balance that really works.

Unfortunately, the WB is a set of 2 multipliers (the 3rd, green one is usually set to 1) so you need 2 sliders to set it. A change in one value requires a change in the other to make the shot look right.

QuoteOriginally posted by ihasa Quote
Life's to short to shoot grey cards...
In 99.9% of situations - you are completely right. I was referring to this troublesome 0.1% .

06-25-2011, 10:14 AM   #24
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White Balance refers to the ratio of rgb channel multipliers. For example, the 5200K setting in Canon 5Dc gives multipliers of red=1.980469, green1=1 blue=1.471680 green2=1, the ratio is 1.980469:1:1.471680:1. Note that is a ratio. The actual multiplier numbers can be adjusted up & down to prevent blowing highlights when multiplier is applied, but the ratio of the multipliers remains constant.

Motion Picture film industry used incident light meters that measure the light for each color channel of rgb to get the multipliers to apply correct white balance.

QuoteQuote:
[...] Using a grey card for exposure is taking an incident light reading, which will always be more accurate than a reflective light reading.
Sorry, but no, a gray card reading does not measure incident light. The meter is measuring reflected light from a surface of known reflectivity (12-18% for gray card).

Makes no difference white or gray card used to set white balance -- the white balance measurement is not the exposure measurement, but the measurement of the ratios between rgb.
06-25-2011, 04:57 PM   #25
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QuoteOriginally posted by Marc Sabatella Quote
As for checking quality of pictures in camera, find that awb does a good enough job for that except in the worst kinds of stage lighting. And in those cases, there is no in camera wb adjustment that would help.
Manual wb adjustment helps *a lot*. If you do it before the shot, of course.

QuoteOriginally posted by Howdy Quote
The keyword here is: "usually"...
Exactly. Usually, the AWB is good enough. But in some cases it never quite works. I have two scenarios where AWB doesn't work:

- indoor portraits under artificial light - I never get the right skin color, even with the K-7 which has pretty good AWB. And if you mess WB, it becomes hard to judge sharpness - but if you manually set it for each room, it works really well.
- use of adaptall lenses in cloudy conditions - must have something to do with the BBAR coatings, but I get colder WB which makes grays look purplish and then it's hard to figure out whether you got PF or it's just a problem of WB
06-26-2011, 06:01 AM   #26
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This is very informative.

I do have a problem with flash WB though. I have a cheap Vivitar 383 clone (Digital Concepts? 952) that works great. The color seems just right in/outdoors with my k7 set to 'Flash' WB, but my new Metz 58 AF-2 seems to vary a little. What bothers me most is I've seen varied WB in an individual photo with the Metz. I think it's because it doesn't 'overpower' a scene and allows for less light than the other flash. Not sure, just started seeing this, but most of the time the Metz is fantastic.

My biggest issue right now though is setting manual WB with a hot shoe flash. I need larger cards than I usually have with me when I try to setting manually. How do you normally accomplish this?

Thanks
06-26-2011, 08:09 AM   #27
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I would start from the simplest solution - photograph your white balance card and use the photo to set the WB of the scene in post-processing. Obviously Raw is necessary (it can be done with a JPEG, but Raw is vastly superior for this).

If it does not help, see if you have other sources of light (like a sun). If so, try to remove those. If it is impossible, welcome to hard-to-do stuff . You may try gelling the lights (see e.g. the article on Strobist ). You will probably have to WB parts of a picture (the one in which the flash dominates and the one with the sun) separately and layer-mask it to look OK. Be prepared for a lot of work...
06-26-2011, 12:13 PM   #28
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QuoteOriginally posted by Howdy Quote
I would start from the simplest solution - photograph your white balance card and use the photo to set the WB of the scene in post-processing. Obviously Raw is necessary (it can be done with a JPEG, but Raw is vastly superior for this).

If it does not help, see if you have other sources of light (like a sun). If so, try to remove those. If it is impossible, welcome to hard-to-do stuff . You may try gelling the lights (see e.g. the article on Strobist ). You will probably have to WB parts of a picture (the one in which the flash dominates and the one with the sun) separately and layer-mask it to look OK. Be prepared for a lot of work...
Thanks Howdy,

I understand and agree with you, I'm just wondering if other photographers hold a white/grey card at arms length and set their WB manually with a shoe mounted flash, and if so what is the results, good, bad, consistent, etc...

With natural light I try to find a white object that directly reflects the light I'm using instead of pulling out the cards, but I don't have much experience with a flash as good as the Metz, so I'm learning.
06-26-2011, 03:01 PM   #29
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Why do you need / want to hold it at arms length instead of photographing it with the subject?
Just in case, see the WhiBal user guide PDF (the procedure is identical for all WB cards).
QuoteOriginally posted by Snydly Quote
With natural light I try to find a white object that directly reflects the light
You risk clipping and metamerism problems but in reality it works rather well. Still the proper (i.e. spectrally flat) WB card should yield more predictable results (not that anyone would care for 99% of shots - the problem is with the remaining 0.1%).

Also, do not underestimate the power of Pentax Auto WB - it is often surprisingly good!
06-26-2011, 07:56 PM   #30
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QuoteOriginally posted by Howdy Quote
Why do you need / want to hold it at arms length instead of photographing it with the subject?
Just in case, see the WhiBal user guide PDF (the procedure is identical for all WB cards).
You risk clipping and metamerism problems but in reality it works rather well. Still the proper (i.e. spectrally flat) WB card should yield more predictable results (not that anyone would care for 99% of shots - the problem is with the remaining 0.1%).

Also, do not underestimate the power of Pentax Auto WB - it is often surprisingly good!
I'm thinking out loud. I usually have a 50-135 on my camera, and to get it to see/focus on a WB card or piece of white paper I seem to have to hold it away from the camera. In addition, the flash needs to light the WB object, and with the hood on the lens I feel as though you need to hold it further away to to preclude a shadow on the image which alters the exposure at least, and possibly the WB or ability to get an acceptable result. Just wondering how others do this.

Thanks for the reference to whibal. Looked it over and it's helpful.


Bill
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