white-balancing of TIFF/JPEG

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It is a known issue that white balancing of tiff and jpeg files brings colour crossover. Each and every day I see photos where a neutral mid-tone object was used to establish white balance, and as a result all colours in shadows and highlights are screwed.

White balancing is essentially a linear operation of multiplication, and as such it is better to use linear colour space for it. One needs to convert image to 16 bits, and then to an appropriate linear colour space (same matrix, but with gamma = 1); and after that to do the balancing. Same way as it is done in RAW.
 
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Dear Rory,

Here is how a wall may look under FL light:
Subscribe to see EXIF info for this image (if available)

Please bring the image to PS, as it is Adobe RGB, and choose eyedropper tool (press "i") to see the anchor point I will use to adjust the tint.

Here are layered PS files to show the mid-tone correction:
http://www.rawmagick.us/crossover/shadow_BalancedInRGB.psd
http://www.rawmagick.us/crossover/shadow_BalancedInLab.psd

As you see, the file balanced in RGB shows different tints in shadows and highlights, and only the midpoint it is balanced in is really neutral; while file balanced in Lab (which is linear space) maintains neutrality across the gradient.

Lab is very useful for this purpose also because moves accomplished in "a" and "b" channels will never throw away luminosity information, hence nor shadows nor highlights will be sacrificed for the sake of colour balancing.
 
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Dear Paul,

To eliminate colour cast one needs only one point if it is done in Lab.

In non-linear colour space, indeed, separate addressing of highlights, midtones, and shadows is needed. However, it is usually a difficult prcedure, as there are not enough reference points.

One of the most difficult tasks in colour correction is to determine if the image has a colour cast. Histograms are essentially useless and misleading for this, as histogram shows that details are lost, but does not show what are those details.

If different tones of the image have different colour casts, like bluish shadows and yellowish highlights (this can be generalized to having 2 or more light sources in the scene, all with different spectrum), then several adjustment points are needed to eliminate the problem - even in Lab, where it is easier, especially using channel blending in overlay mode. But once more, setting perfect colour balance for scenes with complex or distinctive light can kill the atmosphere.
 
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Dear Paul,

Getting rid of the constant cast in Lab is a cleaner and easier solution - it might be not a subjective, but rather a mathematical observation :)

One example of intentionally skewed white balance is when I take photos of monotone objects, like red flowers. If I expose for red, I end up with very few details in blue and green. So, I use complimentary (cyan) filter, and/or skew the white balance to warmest. Result is that I have a "tint". If reds are strong, raw processor might blow them up while counteracting the tint with white balance tool. In this case the rest of colour correction should be addressed in PS.
 
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Iliah said:
As you see, the file balanced in RGB shows different tints in shadows and highlights, and only the midpoint it is balanced in is really neutral; while file balanced in Lab (which is linear space) maintains neutrality across the gradient.

Lab is very useful for this purpose also because moves accomplished in "a" and "b" channels will never throw away luminosity information, hence nor shadows nor highlights will be sacrificed for the sake of colour balancing.
Thanks very much Iliah. I really appreciate you're "advanced" education.
 
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Iliah, I downloaded your files and tried to duplicate your experiment. After one converts the original image to the lab profile, what does on do next? If I take the eyeballs off all the layers except for the lightness one, my image looks similar to your last one but the black and white in your example are darker and lighter respectively.

Does this mean my original sampling point is off or is there something else here I should be doing?

Plese advise.

Thanks, Virginia
 
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Dear Virginia, you have to use curves (I used an adjustment layer in my example), and compensate "a" and "b" so that they are =zero in the sampling point.
 
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Iliah said:
Dear Virginia, you have to use curves (I used an adjustment layer in my example), and compensate "a" and "b" so that they are =zero in the sampling point.
Now we're getting somewhere. I suspect only a very few people know what
compensate "a" and "b" so that they are =zero in the sampling point. means. Would you/or anyone who knows please elucidate, without photoshop jargon. Please understand, I'm not being a smart aleck, but rather than an esoteric discussion among experts simplified wording and not skipping steps would benefit everyone.

Thanks, this is a very valuable thread; I'd like to learn this technique.

Rich
 
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Dear Rich,

If you will open .psd samples, double-click the curves layer, and look at "a" and "b" channels adjustments ... :)

Some useful shortcuts, if we are starting from scratch:
To open Info palette, F8
To convert to 16 bit Lab, Alt-imn Alt-iml
To choose eyedropper tool, press "i"
Set eyedropper to 3x3 or 5x5, depending on the amount of noise on the image
To open curves, Ctrl-M
To set an anchor point in Info palette, Shift-click on the on the region of the image that is supposed to be neutral
To go to "a" channel, Ctrl-2
To make corner point active, Ctrl-Tab
To make "a" value equal zero (watch the info palette), arrows up/right on the lower left corner point; or left/down on the upper right point
To go to "b" channel, Ctrl-3
To cycle through corner points, Ctrl-Tab;
To make "b" value equal zero, use arrows.

I will be happy to provide further explanations if it will be necessary.
 
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Thanks, Iliah, this last bit helped although I got there via a slightly differently (I'm not as familiar with all the PS shortcut as you are). I didn't initially understand what you meant by corner points. For any one else who is confused (hope I'm saying this right, Iliah), they are the absolute black and white points in the a & b channel.

Now I have an image that resembles the last one you posted.

Thank you for your patience, Iliah. You've come to my rescue again!

Virginia

Iliah said:
If you will open .psd samples, double-click the curves layer, and look at "a" and "b" channels adjustments ... :)

Some useful shortcuts, if we are starting from scratch:
To open Info palette, F8
To convert to 16 bit Lab, Alt-imn Alt-iml
To choose eyedropper tool, press "i"
Set eyedropper to 3x3 or 5x5, depending on the amount of noise on the image
To open curves, Ctrl-M
To set an anchor point in Info palette, Shift-click on the on the region of the image that is supposed to be neutral
To go to "a" channel, Ctrl-2
To make corner point active, Ctrl-Tab
To make "a" value equal zero (watch the info palette), arrows up/right on the lower left corner point; or left/down on the upper right point
To go to "b" channel, Ctrl-3
To cycle through corner points, Ctrl-Tab;
To make "b" value equal zero, use arrows.
 
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Iliah said:
Dear Rich,

If you will open .psd samples, double-click the curves layer, and look at "a" and "b" channels adjustments ... :)

Some useful shortcuts, if we are starting from scratch:
To open Info palette, F8
To convert to 16 bit Lab, Alt-imn Alt-iml
To choose eyedropper tool, press "i"
Set eyedropper to 3x3 or 5x5, depending on the amount of noise on the image
To open curves, Ctrl-M
To set an anchor point in Info palette, Shift-click on the on the region of the image that is supposed to be neutral
To go to "a" channel, Ctrl-2
To make corner point active, Ctrl-Tab
To make "a" value equal zero (watch the info palette), arrows up/right on the lower left corner point; or left/down on the upper right point
To go to "b" channel, Ctrl-3
To cycle through corner points, Ctrl-Tab;
To make "b" value equal zero, use arrows.

I will be happy to provide further explanations if it will be necessary.

Thanks for your explanations. It works very good i will do some testing on some photo's with color casts thanks for this information Iliah.

And maybe a off topic question i want to buy studio equipment and i see alot of people use a color chart checker (macgrabeth or kodak). Is it adviced to buy such a card to get colors right and white balance. And would it then be also better if i use such a card to use white balance correction from the first photo that is shot with the color chart in LAB mode?

Thanks for your help allready.

Greetings,
VinceBeus
 
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Dear Virginia,

You are exactly right, though "a" and "b" are pure colour channels, and I do not know whether "black" and "white" are appropriate terms in English in regards to those. Anyway, here is a picture:

Subscribe to see EXIF info for this image (if available)


I referred to those points highlighted in green as "corner points"
 
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Dear Vince,

For digital studio I would say:

http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=27715&is=REG
better yet, purchase a sample of N8 from Gretag Macbeth (call them at 1-845-565-7660)

http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=325038&is=REG

http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=26662&is=REG

Very promising, but lacking good software support for digital camera applications/profiling is
http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=325039&is=REG
Still, it works very well in studio environment, under constant lighting conditions
The least useful is
http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=325035&is=REG
as it is designed to be a reference for eyeballing, and have not enough reference points for any serious calibration in digital environment.

"90% method" is heavily criticized, BTW :)
 
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Iliah said:
Dear Vince,

For digital studio I would say:

http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=27715&is=REG
better yet, purchase a sample of N8 from Gretag Macbeth

http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=325038&is=REG

http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=26662&is=REG

Very promising, but lacking good software support for digital camera applications/profiling is
http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=325039&is=REG
Still, it works very well in studio environment, under constant lighting conditions
The least useful is
http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=325035&is=REG
as it is designed to be a reference for eyeballing, and have not enough reference points for any serious calibration in digital environment.

"90% method" is heavily criticized, BTW :)
Ok thanks for the information i will look it up. And i did not know if i was right about if it was the 90% method. But i use to use that because i started last 2 months focussing more on the White Balance then before. So i try to get the white balance right when i take the photo's. And it is great to learn new things like your explanation of white balance adjustment for Tiff files. I am going to read and look at all the links you gave me.

Greeatings,
VinceBeus
 
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I saw this one is older version and think i buy this one because it is cheap:

http://shop.colourconfidence.com/product.php?xProd=1224&xSec=95

This one is the macgrabeth color chart the image is just standard but the company have confirmed it earlier on they also sell a german version what is 100 procent identical they say:

http://shop.colourconfidence.com/product.php?xProd=1239&xSec=30

And the other one you mentioned the white nuetral black kind of car (whitebalance card) i saw at other store.

I think these cards are ok to work with for the beginning and maybe later on if they are not fully satisfy i look for better solutions. But i think wb metering and setting all equipment good is allready good beginning for working with studiolights.

Greetings,
VinceBeus
 
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