UniWB with DxO

[Cerebus]

Greetings:
Just joined these forums, which I discovered in my search for info about UniWB. Now that I have my Sony A900 all set up, there's one part of the equation left I'm hoping someone can help me with. I'm using DxO as my raw converter, and I'm puzzled as to how to specify a linear tone curve. Do I just leave the tone curve alone in the Tone Curve tool? Is the default a linear curve? Does DxO Lighting, exposure and other tools affect the tone curve as well?

Also, I can get rid of the green cast using the Daylight preset. Am I correct in assuming that white balance is independent of a linear tone curve?

Any help appreciated.


thanks,
eric

 

[Dave_Anderson]

While I don't have DxO yet, I'm curious about this as well.

FWIW, I read the UniWB technique as more of an exposure aid. So, using your UniWB setting, you push your histograms as far to the right as you can manage without clipping, note the exposure setting, then you can go back to the appropriate WB setting for the conditions and expose at the noted setting.

While some(esp. Iliah) just shoot using UniWB, I have found that it can be difficult to get back to appropriate WB using Raw Therapee or IDC.

My understanding is that the RAW data is the same regardless of the WB setting, but having a more nearly "correct" WB setting at the time of the exposure provides the appropriate metadata to help your RAW processing software start off "in the ballpark".

The advantage to exposing with UniWB is that there is less fiddling needed, a boon in changing light. The advantage of metering with UniWB then exposing with appropriate WB is that RAW-rookies like me have an easier time in PP.

 

[Jamesmd]

Hi , the data in Raw file isn't the same wth unwb , there is a great difetence , because R G B didn't have any factor aplayed , so not only the histogram in cameras histogram is more acurate but I velive there is less noise to , ore should be , because R for example with no factor will be then more exposed , more light less noise .

James

 

[Dave_Anderson]

James, my understanding is that the only difference is the gain factors that are supplied to the RAW processor are simply set as close to "1" as possible with UniWB, essentially giving you the "native" WB of the sensor. The purpose of this is to get the camera histogram to stop lying to you, which it does when it displays the histogram based on the JPEG and WB settings already applied. Also, I understand that RAWanalyze is the only tool that shows the true RAW data without using gain factors at all, which explains why a difference between UniWB and say daylight for example is seen in RT, LR, IDC, etc. all of which use the gain factors whether you want it or not.

Once I get my camera back from repair I'll experiment with RAWanalyze and a couple of test shots. Unfortunately I don't have any "same composition, same exposure" shots to compare with at this point.

I am happy to learn and re-educate myself where I'm wrong. Most info I've seen on this seems to be derived from this page and this one. I am interested in any further info you may have.

I just found this, will dig through it when I can find the time.

 

[Jamesmd]

Hi Dave , I read all of this some time ago , I'll find where and let you know , it might be in Spanish .

I understud that when you cancel wb in camera , no " filters " are aplayed to raw , sow r g b was kept linear , but I might be wrong , but for sure r g specialy where more exposed ,1 to 1.5 stop , than with wb aplayed .

But this colud be just for exposing better due to a better histogram representation as r and g are normaly higher with normal WB.

It is true that with uniWB and raw converter with wb disabled the color is right ( all most ) so you probably are right and noise improvement is because you simply expose more to the right this way .

Let me know if you find out , I'm going to read the links you gave . Thanks

cheers

James

 

[Jamesmd]

Yes , I read the same as you . I went thru it again and , yes I think you are right , so sorry about that . I should of read again before answering.

Well , very interesting theme this is , specially if you like triying things .
Please let me know when you do your tests .

Sorry again for the confusion Dave.

Cheers

James

 

[Dave_Anderson]

Thanks for checking me on that, James. Good to know I wasn't reading it all wrong. That's how we learn, poking, prodding, questioning. :thumbup:

I have found that with RT, and shooting with UniWB, I often end up with my sliders way out of whack just trying to get the image in the ballpark. I think that one way to mitigate that is to create an ICM profile, though for now the easy way is to expose with appropriate WB.

I'm also looking into creating some inverted ICM profiles to aid in digitally capturing some of my old negatives. The problem there is, when I invert the luminance(?), all of the other sliders are then reversed. I read somewhere that this can be resolved with an ICM profile that performs the initial "color invert" along with some basic corrections.

 

[Jamesmd]

Hi Dave , if I tell ypu the truth I think uniWB is a great idea but it's better to wait for it to be a standar option in camera and converters .
I used it to have a shot in camera done with uniWB ( then checked in raw converter ) and use it to find the setting in camera that gave me the most similar histogram to the uniWB as it's easy to compare that way switching from one to other .

Cheers

James

 

[Dave_Anderson]

James, IMHO it's not really something I want to use for every shot. Firing off a bracketed set of a difficult scene can get you "good enough" results 99% of the time, I'm thinking.

UniWB is most interesting for me as a way to maximize DR without clipping highlights on a very difficult scene. I think I will eventually get used to looking at the normal histograms and being able to judge how close I am to clipping, but some time spent playing with UniWB ought to help me be a better judge of that.

Funny how things work out. Back when my budget was far more limited than it is now, I would burn through 2-3 rolls of slide film on improvised test targets, just trying to get a handle on a new lens's DOF, colors, diffraction, etc.

Now that money is not as much of an issue, time is my most precious commodity, in the shortest supply -- and now, I am awash in new software packages that more than anything require time and patience to master.

It's a bit ironic but fortunately I have a good background in imaging SW and I learn quickly.

 

[Jamesmd]

Yes sir , time is the most precious treasure !!

James

 

[douglasf13]

I've just started trying DxO, and I'm finding that I can nearly match my camera's histogram with DxO's if I dial down exposure in DxO around -1EV and turn off Dxo lighting, but I need to test more. I'm not sure if you can start with a truly linear curve like with RT or C1. As far as WB is concerned, Dave is right that it's in the RAW converter where the multipliers are added. I've adopted Jono's style of WB, and just use daylight for nearly everything except tungsten, and it has brought a more "film" feel to my photos. So, I can shoot with uniWB, and then just to a global daylight WB setting in the converter (and tweak if need be.)

FWIW, Iliah talks a lot about exposure to the right, and, he feels that sometimes people take this too literally, and should actually be exposing MORE to the right. ie, blowing highlights in order to preserve detail in the midtones. Obviously, it's subject dependent. If you spot meter your subject at around +.5EV, or spot meter your detailed whites at +2.5EV, you should be in good shape with the A900.

 

[Cerebus]

I had dropped a note to Thom Hogan regarding the use of a Linear curve and his response was that the Linear curve was used in camera to help get an accurate histogram. There's a way to load a linear curve in some Nikons apparently.

Doug, I'd certainly be interested in learning about your DxO settings. I've started to use the No Correction preset and then working from there. I'll try turning down the DxO lighting even more. I'm also going to experiment with switching from Zone -1 to Zone 0 and using exposure compensation to get more light for automatic metering.

 

[Dave_Anderson]

Doug, can you post a pointer to the "Jono style" WB that you are referring to? I'm always interested in hearing about others' techniques. Also, have you done any LR <-> DxO integration? I seem to be a small minority wanting to go this route as I opened a thread on the subject that is steadily making its way to the bottom of the first page in this forum

I'll give it a bump and see if anyone notices.

 

[Jamesmd]

Hi Douglas, at the moment I found the better way to expose is center weighted for the highest lights to indicate +2 , +2.3 . Do you think its ok or am I going wrong ? ( I ask you because you have much more experience than me )

Thanks

 

[douglasf13]

Cerebus, I also started with the no correction setting, and I've found that DxO definitely has some built exposure compensation (like Lightroom,) and it seems to be around one stop EV. Other than that, I'm still experimenting with settings, although, I'm about to give up on DxO. I really like the lens correction, and it is great for high ISO, but it isn't very stable on my machine. I think that I'm going back to C1. As far as -1 Zone is concerned, in RAW it really just adds +.5 EV to your exposure, and I've decided to go back to regular ZONE and set contrast to -3, and I just add +.5EV to all of my shots.

Dave, Jono's WB style is simply (nearly) always use daylight or tungsten WB. AWB can cause odd color shifts in mixed lighting, and using mostly daylight WB really allows me to get a feel for the camera's color. Every once in a while I tweak it in RAW, but most of the time I use daylight WB, with the occasional tungsten WB when necessary.

James, to tell you the truth, I'm not sure I've ever used center weighted metering, so I can't give you much help with that, but it seems like if you're aiming to meter a small part of the scene, spot would be the more accurate method.

 

[Jamesmd]

Douglas , it would be great if you could give it a try , I really think it makes life easier in most the situations ,.

Thanks

James

 

[douglasf13]

Douglas , it would be great if you could give it a try , I really think it makes life easier in most the situations ,.

Thanks

James

I'll play around with it, but, since I usually use zone metering, the smaller the exposure area that I have, the better, so spot metering makes more sense for me.

 

[Dave_Anderson]

Thanks Doug, I tend to stick with daylight, tungsten or flash WB to keep it simple. What OS are you running, where you are seeing DxO stability issues? What circumstances seem to cause the issue? Also, are you using the latest DxO, 5.3.5? The support person I asked about the a900 green cast/a900 issue hinted that there was something "big" coming this fall. 5.3.5 is supposed to fix the green cast but the impression I had was that something much bigger was imminent.

 

[douglasf13]

Yeah, I'm using the latest version of DxO. I'm currently using Windows XP. My issues usually come when I zoom in to 100% and move around the image.

 

[Dave_Anderson]

Hmmm... Have you considered the possibility that it could be a video driver issue?