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Old Jun 20, 2009, 11:59 AM   #1
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Default Maximizing your dynamic range shooting raw A700

Reading a few post recently I came across discussing a setting called "uni white balance". The theory behind this is you can widen your dynamic range thus having fewer blowouts and shadow loss. Plus widening your dynamic range allows you to expose to the right further pulling up the darker areas of the image so you end up with less noise.

Has anyone here tried this?

From what I have read the way to accomplish this is to first set set camera (A700 & A900) to take a custom WB in one of your 3 custom WB settings.

Aim camera at any bright light and shoot at widest aperture and slow shutter speed to blow out the entire image.

The camera will notify you that there is an error but ignore it and set the WB to one of your 3 custom settings.

Now all shots (in raw) will appear to have a green color in the LCD. To get a more accurate LCD review set your Creative Style to:


-- Neutral
-- Contrast -3
-- Saturation -1
-- Sharpness ?

Remember that your RAW converter will most likely add adjustments during import so you will have to adjust it to your liking. I would think that you would want to import your photo's without any adjustments if possible but thats only my opinion.

Please add too or correct anything that you can. This really looks like a way to maximize your cameras potential.

More dynamic range with less noise sounds worth trying.
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Old Jun 20, 2009, 12:54 PM   #2
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If you're shooting raw, White balance is nothing more than a set of RGB Multipliers stored in the metadata of a raw file. Virtually all camera manufacturers use the same technique (store the actual RGB Multipliers they want to apply later).

The raw converter then applies these RGB multipliers (for example, 2.15, 1.1, 1.27) to the red, green and blue channels of an image during the demosaic process if you elect to use the "as shot" white balance (versus setting it yourself).

If you want to see the multipliers being applied, some raw converters can show you that information (for example, UFRaw shows you the RGB multipliers being used if you go to the screen for setting WB and you can see how your changes impact the "as shot" multipliers it found in the metadata)

IOW, using a custom white balance shouldn't do anything more than you could do in post processing by adjusting the multipliers being applied yourself if you're shooting in raw. I usually set my white balance (either preset or custom) to the temperature of the lighting so that the raw converter can use it if I think Auto is going to be off very far.

As for other settings like contrast and sharpening, they wouldn't impact the raw file, either. But, many raw converters can use a custom tone curve if desired. Now, some raw converters may take those settings into consideration and try to apply them during the demosaic process. But, usually, most converters are going to ignore everything except for the White Balance (which you can change since it hasn't been applied to the raw data), unless you're using the camera manufacturer's converter. But, I've never even tried Sony's converter with my Sony A700's raw files.

Now, I can remember when Nikon caused a stir (because they started encrypting the "as shot" White Balance multipliers, with some developers wondering if they were using a different approach).

After developers cracked the encryption, it turns out they're still doing it the same way, too (although they do have a secondary section designed for a second set of RGB multipliers in the metadata, it's not being populated yet the last time I checked with developers).

Now, it's possible that some modification of the raw data is happening. For example, I have seen developers report on evidence that Nikon has applied multipliers to some of their raw files prior to any demosaic process (probably to help keep noise levels in check if I had to guess). Ditto for Sony (they even sell noise reduction at the raw level as being an advantage with many newer cameras). But, I really doubt that that your WB settings have any impact on the raw data itself with Sony's files (even though many converters can use those settings when applying RGB multipliers during the conversion).
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Old Jun 20, 2009, 1:09 PM   #3
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If you see any evidence of it, I'd be interested in seeing it. But, I'd be *very* skeptical of what you read about that type of thing.

Chances are, if you use a raw converter capable of a linear conversion with no custom tone curves or anything else being applied during the conversion process, you'll see that those settings make zero difference in the output (IOW, you could tweak the settings in the converter yourself and come up with the same result, since the raw data from the sensor is not being modified).
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Old Jun 20, 2009, 1:38 PM   #4
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My take on this is that blowing out all channels (RGB) to 256R-256G-256B would balance out all 3 channels.

Then the green channel would most likely be the first to blow out because there's more green in the bayer pattern, with that you could push exposure to the right pulling up the red and blue farther then using a preset thus gaining at least a stop in DR and lowering noise.

Maybe this will explain things better

White balance is multiplication of linear raw data to equalize sensitivity of sensels of different colour groups to render greys as greys.

UniWB is setting WB multipliers to all 1's and is meant to be a workaround for 2 major problems:

1. Histogram distortion with white balance application.
Cameras show a histogram based on JPEG preview, while JPEGs have white balance applied to raw data. If you want to use histogram to judge exposure, this white balance application prevents from the proper evaluation of the real exposure problems.

2. Many raw processors have problems scaling data due to incremental white balance application. Say, white balance is applied causing overflow in a channel. When we start adjusting white balance the lost information in the highlights can't be recovered as it is lost during white balance application at the first stage. Same goes to applying negative "exposure compensation" in a converter to a channel that is already blown out due to white balance (sequence of operations error, negative "eV" in a converter should be applied before white balance, but to speed things up and to use less memory it is not always the case, same as incremental application of white balance saves memory but causes irrecoverable overflows).

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Old Jun 20, 2009, 1:46 PM   #5
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It appears to give a better more accurate histrogram while shooting in raw?

Any opinions?
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Old Jun 20, 2009, 1:48 PM   #6
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That multiplication doesn't take place until you use a raw converter. It's only a set of multipliers being stored in the metadata.

Now, some cameras will apply it to the embedded jpeg thumbnail, and it could impact your histogram. That's one reason to set it for the temperature of the lighting you're shooting in. ;-)

But, the settings in the camera have no impact on the actual data stored in the raw file (only the multipliers that are being stored in the metadata are being modified, and they're not being applied to the raw data by the camera).

You could set the multipliers any way you want to *before* they're ever applied using a number of raw converters. IOW, you're just creating extra work trying that approach. ;-)

I'd be *very* skeptical that any camera manufacturer would attempt to apply any multipliers to the raw data itself based on your WB settings. Then, you would be risking blowing individual channels if the camera got it wrong and you needed to change it later (defeating the benefits of shooting raw to begin with). ;-)
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Old Jun 20, 2009, 2:10 PM   #7
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Quote:
Originally Posted by JimC View Post

You could set the multipliers any way you want to *before* they're ever applied using a number of raw converters. IOW, you're just creating extra work trying that approach. ;-)
Thanks Jim.

I don't like extra work.
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Old Jun 20, 2009, 2:33 PM   #8
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The one point I do agree on with uniWB is you get a more accurate histrogram to the raw information then the histrogram you'll get displayed on your viewfinder after the in camera JPEG conversion.

Also the extra work might only be setting up your raw converter initially to import your raw files directly from your camera without any changes, or the changes you set manually.
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Old Jun 20, 2009, 2:34 PM   #9
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If you're trying to maximize DR and don't like tweaking curves in your raw converter of choice (or don't want to use a Linear conversion which can result in a very "flat" output), you may want to try using a custom curve instead.

Some raw converters using Dave Coffin's dcraw.c as a base can apply a custom curve during the conversion process.

See the "Base Curve" section of this user guide page for UFRaw and you'll see an example of an image using a custom curve known as the "White Wedding" curve (you can "mouse over" the image to see the difference it makes in retaining highlight detail). That way, you wouldn't need to tweak curves yourself.

http://ufraw.sourceforge.net/Guide.html
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Old Jun 20, 2009, 4:47 PM   #10
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I like starting out with a "flat" raw file. That way you can adjusted to desired result. I don't know if that would be considered linear or not.

As mentioned in an earlier post I use cRAW neutral with -3 contrast and -1 saturation and 0 sharpness.

When I import the raw files into aperture 2, I choose apple-camera default. I have no idea what apple-camera default does as far of making adjustments to the JPEG preview. I hope it does not add any adjustments.

Last edited by lomitamike; Jun 20, 2009 at 4:52 PM.
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