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UniWB - Is it worth the trouble?
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Apr 6, 2021 13:24:19   #
selmslie Loc: Fernandina Beach, FL, USA
 
There is a lot of confusion surrounding UniWB.

1. Most of the attention given to it concerns how to set it up which can be easy or difficult depending on who describes it.

2. Very little attention is given to what it actually does and how to use it if you get it set up.

3. Finally, almost no attention at all is given to whether it actually accomplishes anything useful.

I found a simple way to set my Nikon Df to Daylight and UniWB. I then captured a scene based using each WB setting. The scene was chosen because it contains an extremely reflective white PVC fence, brighter than any sunlit cloud or white bird.

Both images were exposed at 1/250s f/11 @ ISO 100, 1/3 stop darker than Sunny 16. Although the camera was not mounted on a tripod, the exposure and ISO were identical in each case so both raw files are virtually identical.

In fact the two luminance histograms on the camera were very similar since they are based primarily on the green channel. However, there is a slight difference in the far right end of the histograms:

Daylight WB

UniWB

Looking at only the luminance histogram you might be tempted to increase the exposure a little. But as you will see, this might be a mistake.

What can we learn from the RGB histograms?

Daylight WB

UniWB

The main difference is that in the UniWB histograms the red and blue channels are pushed significantly to the left leaving the green and luminance channels where they were - almost.

Since the two raw histogram displays are identical except for the associated image we need only one of them:



You can see from the raw histograms that it might be possible to add about 1/3 stop to the exposure and actually use Sunny 16 - 1/200s f/11 ISO 100. But that's all. Any more and the green channel will blow out.

But if you look at the camera's histograms, the Daylight WB version already told us that. UniWB didn't actually tell us anything significantly different from what we could see in the Daylyght WB version in the camera's display.

There was no way that we could expose any than maybe 1/3 stop further to the right and that would not make the raw data visibly or measurably better.

So the bottom line is that there is no demonstrable benefit to UniWB.

Apr 6, 2021 13:26:03   #
selmslie Loc: Fernandina Beach, FL, USA
 
Here are the two JPEG images SOOC.
Daylight WB
Daylight WB...
(Download)
UniWB
UniWB...
(Download)

Apr 6, 2021 14:43:54   #
 
 
Apr 6, 2021 15:34:23   #
selmslie Loc: Fernandina Beach, FL, USA
 
quixdraw wrote:
https://www.dslrbodies.com/cameras/nikon-and-dslr-camera-faq/what-is-uniwb.html

The article states that, "Thus, by using UniWB you get accurate histograms and highlights for your raw data." That begs the question, how are they "accurate"?

He goes on to claim, "The camera companies don't understand that photographers might actually want the correct data." What make it "correct"?

The JPEG histograms will never match the raw histograms regardless of the white balance setting because it's impossible.

The raw data has a linear response in all three color channels - they increase by a fixed amount with each doubling of exposure and they stop increasing when they reach a [14-bit] value just below 16383 (-1+2^14).

Since they can't be directly plotted along with the JPEG values I converted the raw values with a simple equation - (256/14)*log(raw,2). Here is what we get for the Df as we record a standard white target in one stop increments from EC-4 through EC+4.



The raw plots (dashed lines) are linear. The JPEG plots (solid lines) are straight from EC-1 through EC+3 and follow a curve below EC-1. This gives the JPEG more contrast from mid-tones through highlights and less contrast in the shadows below EC-1.

The JPEG reaches its maximum value (255) less than 1 stop earlier than the raw file. And the green value is always brighter than blue which is brighter than red. But the JPEG response is not. Nevertheless, the JPEG lines are much closer together than the raw lines. All three lines cross the EC+0 level close to 127.

But here is what happens when we use UniWB:



The raw plots are virtually identical except for some slight sampling error because WB does not affect the raw values and it doesn't influence the camera's meter.

But the JPEG plots are pulled apart to provide brighter green and darker blue and red pots. This emphasizes the the importance of the green channel which represents 50% of the luminance for a Bayer array (it's 56% for an X-Trans array). The red, green and blue values at EC+0 are about 33, 139 and 83 respectively.

Since the JPEG values are used to create the JPEG histograms it's almost impossible to rationalize that they are either "accurate" or "correct". In fact, they are as useless as the greenish JPEG image itself.

Apr 6, 2021 22:25:08   #
Ysarex
 
selmslie wrote:
So the bottom line is that there is no demonstrable benefit to UniWB.

Don't you mean there's no benefit to UniWB that you can demonstrate using your camera and it's features? If I didn't know you better I'd suspect you were blowing thick clouds of sophist smoke while grinding your axe.

Apr 7, 2021 04:38:01   #
selmslie Loc: Fernandina Beach, FL, USA
 
Ysarex wrote:
Don't you mean there's no benefit to UniWB that you can demonstrate using your camera and it's features? If I didn't know you better I'd suspect you were blowing thick clouds of sophist smoke while grinding your axe.

Just because it's over your head does not mean that my analysis is wrong.

The numbers are slightly different for each camera but the overall effect is the same. It behaves the same way with my D610 and Z7.

I even looked at it with the Fuji X100T and got the same results. The RGB values for middle gray in the JPEG are 36, 188, 142.

I would suggest that you do some experimenting on your own but I doubt that you are willing or capable.

Apr 7, 2021 09:52:54   #
selmslie Loc: Fernandina Beach, FL, USA
 
selmslie wrote:
... I even looked at it with the Fuji X100T and got the same results. ...

If you are not convinced by my findings with the Df you might want to try UniWB with your own camera.

The easiest way to set your camera up is to pick a custom white balance based on the display of the UniWB target below, preferably on a calibrated monitor but that's not critical. Some have recommended much more convoluted ways to get this done this is a simple method that works well with my Nikons, my Sony A7 II and my Fuji X100T.

I have included the raw plots for two identical X100T exposures with the two WB settings. The raw histograms are unchanged. However, the camera's JPEG histogram are also the same - only the Luminance version is available in the camera.

UniWB provides no benefit in the X100T.
UniWB target
UniWB target...
(Download)
Daylight
Daylight...
(Download)
UniWB
UniWB...
(Download)

 
 
Apr 7, 2021 11:14:07   #
Ysarex
 
selmslie wrote:
The easiest way to set your camera up is to pick a custom white balance based on the display of the UniWB target below, preferably on a calibrated monitor but that's not critical.

Setting UniWB for any given camera requires a custom target designed for that camera. You should have read that in the Thom Hogan article that quixdraw posted.

I used your target (on a calibrated monitor) and set a custom WB on my SL. The result is a UniWB botch job (see below). Those Red and Blue values should be 1 if you've successfully set a UniWB white balance. 1.3 is not 1.

To quote your original post: "I found a simple way to set my Nikon Df to Daylight and UniWB." Did you now? Well that's so nice. Maybe we're getting to the root of your problem.


(Download)

Apr 7, 2021 12:07:57   #
selmslie Loc: Fernandina Beach, FL, USA
 
Ysarex wrote:
Setting UniWB for any given camera requires a custom target designed for that camera. You should have read that in the Thom Hogan article that quixdraw posted. ...

In my opening post I mentioned that there are three challenges. You can't demonstrate that you can get past #1, even following the instructions you have been able to track down. If you can't get past step #1 you will never be able to get to step #2.

No matter how you set your UniWB all it does is to move the JPEG histograms around. You then need to use those histograms in the field to help you arrive at a proper exposure.

So until you can accomplish #1 and #2 you can't reach#3, a conclusions about whether it is worth the effort.

But all you can do is to look stuff up on the internet. You can neither understand the subject or do your own test.

What can you deduce from these two examples?
Daylight WB
Daylight WB...
(Download)
UniWB
UniWB...
(Download)

Apr 7, 2021 12:14:10   #
Ysarex
 
selmslie wrote:
What can you deduce from these two examples?

That you're engaged in your usual smoke blowing BS and that you never got past #1. Otherwise you'd show the EXIF data and those Red Blue coefficient values for this image: https://static.uglyhedgehog.com/upload/2021/4/6/443108-uniwb.jpg

Apr 7, 2021 12:18:14   #
selmslie Loc: Fernandina Beach, FL, USA
 
Ysarex wrote:
That you're engaged in your usual smoke blowing BS and that you never got past #1. Otherwise you'd show the EXIF data and those Red Blue coefficient values for this image: https://static.uglyhedgehog.com/upload/2021/4/6/443108-uniwb.jpg

I will as soon as you demonstrate that you can do steps #1 and #2 with your own camera.

If you can't then we will all know who is blowing smoke.

 
 
Apr 7, 2021 12:31:46   #
Ysarex
 
selmslie wrote:
I will as soon as you demonstrate that you can do steps #1 and #2 with your own camera.

If you can't then we will all know who is blowing smoke.

You're the one making the presentation and claiming you know what you're doing. Burden of proof is on you. You don't get to play your juvenile school yard games -- grow up. Did you set up UniWB accurately on your camera or didn't you.

What we have so far is a post from you with incorrect instructions: https://www.uglyhedgehog.com/t-692202-1.html#12141373 Happy to leave it at that and call it your usual incompetence.

Apr 7, 2021 14:49:31   #
selmslie Loc: Fernandina Beach, FL, USA
 
Ysarex wrote:
You're the one making the presentation and claiming you know what you're doing. Burden of proof is on you. ....

I already proved my point, that UniWB provides no benefits and it's a colossal waste of time. Now it's up to you to prove otherwise.

But you can't get past step #1. You can't follow Guillermo Lugic (too complicated for you) or the instructions from Kasson in that post that where you claim, "There's easier ways to set up unity WB than the method described by Guillermo Luijk." And you don't have a clue how to follow Thom Hogan's instruction either. It's all too complicated for you. You need someone smarter than yourself to do it for you.

If you could have accomplished #1 you would have been able to proceed to #2 and show us how you can use it to help you with your exposure when using ETTR.

There is no point in trying to explain to you how these examples were made. They are related to this topic in a way you haven't figured out. They are beyond your comprehension. If anyone else asks I will answer them.

Apr 7, 2021 15:00:08   #
selmslie Loc: Fernandina Beach, FL, USA
 
There is no point in trying to explain these to you either.
Tungsten WB
Tungsten WB...
(Download)
UniWB (same as before)
UniWB (same as before)...
(Download)

Apr 7, 2021 15:39:03   #
Ysarex
 
selmslie wrote:
I already proved my point, that UniWB provides no benefits and it's a colossal waste of time. Now it's up to you to prove otherwise.

But you can't get past step #1. You can't follow Guillermo Lugic (too complicated for you) or the instructions from Kasson in that post that where you claim, "There's easier ways to set up unity WB than the method described by Guillermo Luijk." And you don't have a clue how to follow Thom Hogan's instruction either. It's all too complicated for you. You need someone smarter than yourself to do it for you.

If you could have accomplished #1 you would have been able to proceed to #2 and show us how you can use it to help you with your exposure when using ETTR.

There is no point in trying to explain to you how these examples were made. They are related to this topic in a way you haven't figured out. They are beyond your comprehension. If anyone else asks I will answer them.
I already proved my point, that UniWB provides no ... (show quote)

So just more schoolyard whining. Again, it's your presentation not mine. So far what we have from you is a post with incorrect instructions: https://www.uglyhedgehog.com/t-692202-1.html#12141373 Your whining doesn't change that in the slightest. It's not my job to show you how to do it right. I'm satisfied pointing out that you did it wrong.

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