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Archive 2008UniWB
p.1 #1UniWB
i've heard this discussed here and elsewhere but i haven't seen a description of what it is, plus why/how it works.
Can someone please fill me in?
Can someone please fill me in?
Aug 11, 2008 at 10:29 AM
p.1 #2UniWB
Here's a start. It would be great if we can have a consistent set of tutorials in this thread!
http://www.libraw.org/articles/white-balance-in-digital-cameras.html
http://www.libraw.org/articles/white-balance-in-digital-cameras.html
Aug 11, 2008 at 10:47 AM
p.1 #3UniWB
The main use of uniwb as far as I know is to set the prooper exposure for a given photo using the histograms on the camera. The histograms will show the true actual exposure for a given picture as opposed to the values calculated for the displayed photo when you use your camera to determine white balance.
And here is the uniwb files for a D300...
http://www.pochtar.com/Nikon_D300_NearUniWB.zip
Here is a description of what to do...
http://forums.dpreview.com/forums/read.asp?forum=1039&message=27426464
From what I understand, once you have this set up, you can adjust wb in camera raw or NX using the presets it has or the dropper. You can also use the white balance obtained from a grey card at post processing time.
Edited on Aug 11, 2008 at 11:12 AM
And here is the uniwb files for a D300...
http://www.pochtar.com/Nikon_D300_NearUniWB.zip
Here is a description of what to do...
http://forums.dpreview.com/forums/read.asp?forum=1039&message=27426464
From what I understand, once you have this set up, you can adjust wb in camera raw or NX using the presets it has or the dropper. You can also use the white balance obtained from a grey card at post processing time.
Edited on Aug 11, 2008 at 11:12 AM
Aug 11, 2008 at 11:07 AM
p.1 #4UniWB
i have a uni WB preset in my D300. I use it when i work with a gray card in lighting situation that doesn't change much. I make just one shot of the gray card (with the uniWB setting of course). The rest of the shooting i just use the uniWB setting and leave that as it is. All the files will look green. The uni wb is greenish due to the bayer design of your sensor. There are twice the amount of green pixels compared to the red and blue pixels. When i process the files i use the marquee tool in capture nx on my gray card shot to get the proper WB setting. Then i adjust the obtained setting to the other files and they will all have the proper WB setting. It works fine. I don't know if it's better, i'm just experimenting with it and i have some fine results with it. One thing i've noticed is that the red channel isn't clipping as fast as it would with another wb-setting. appearently becasue the uni wb is so green. I have no idea if that helps with my exposure. i don't really use it that often. Like i said: just experimenting 
Aug 11, 2008 at 02:07 PM
p.1 #5UniWB
I think if you just use the usual exposure before using uniwb there will be no real change. Howerver, if you always adjust your exposure to move the histogram to the right, you will get better exposed photos and hence spread the dynamic range over a larger exposure range. This should help the noise as well.
Aug 11, 2008 at 05:44 PM
p.1 #6UniWB
tomb18 wrote:
I think if you just use the usual exposure before using uniwb there will be no real change. Howerver, if you always adjust your exposure to move the histogram to the right, you will get better exposed photos and hence spread the dynamic range over a larger exposure range. This should help the noise as well.
That was my idea too. You'll see that the red channel will not clip as fast as it normally would. Now that's great. But i just wonder: When i process the file i have to adjust the whitebalance, so my red channel will look normal again. Will it not clip after all? I'll try some more testing.
I think if you just use the usual exposure before using uniwb there will be no real change. Howerver, if you always adjust your exposure to move the histogram to the right, you will get better exposed photos and hence spread the dynamic range over a larger exposure range. This should help the noise as well.
That was my idea too. You'll see that the red channel will not clip as fast as it normally would. Now that's great. But i just wonder: When i process the file i have to adjust the whitebalance, so my red channel will look normal again. Will it not clip after all? I'll try some more testing.
Aug 11, 2008 at 11:23 PM
p.1 #7UniWB
Using the uniwb will allow one to expose more accurately for maximum dynamic range. You want to expose to the right as much as possible so that you can have more data for the darker values in the image.
To see how much more latitude you have for example in the reds, take a picture of a red card using auto wb and then uniwb with the same exposure. You will see that you can expose more using uniwb, thus moving the histogram to the right.
When you load this in camera raw, you are applying the uniwb and the histogram you see should be the same as what you saw in the camera. You can then lower the exposure in camera raw and apply a new white balance. Even if this seems to clip the histogram, you can just lower the exposure and the data remains intact. You do not loose the actual data from the raw file. Thus you will use more bits of information for the shadows which is a good thing. This means less noise as well.
Using uniwb just allows you to get the best exposure possible, and avoids clipping since you are seeing the actual raw data contained in the raw file as opposed to a jpeg image that has had the white balance coefficients added.
To see how much more latitude you have for example in the reds, take a picture of a red card using auto wb and then uniwb with the same exposure. You will see that you can expose more using uniwb, thus moving the histogram to the right.
When you load this in camera raw, you are applying the uniwb and the histogram you see should be the same as what you saw in the camera. You can then lower the exposure in camera raw and apply a new white balance. Even if this seems to clip the histogram, you can just lower the exposure and the data remains intact. You do not loose the actual data from the raw file. Thus you will use more bits of information for the shadows which is a good thing. This means less noise as well.
Using uniwb just allows you to get the best exposure possible, and avoids clipping since you are seeing the actual raw data contained in the raw file as opposed to a jpeg image that has had the white balance coefficients added.
Aug 12, 2008 at 07:59 AM
p.1 #8UniWB
i think i have have an understanding of how and why. a big thanks for the links there tomb18. and thanks for some insight Ray. greatly appreciated.
i have the preset saved in my camera, and yes, the images are quite green under daylight conditions. i also tried the preset under incandescent light and got major underexposure in the blue channel. would this be normal and/or expected?
i have the preset saved in my camera, and yes, the images are quite green under daylight conditions. i also tried the preset under incandescent light and got major underexposure in the blue channel. would this be normal and/or expected?
Aug 13, 2008 at 05:57 AM
p.1 #9UniWB
tomb18 wrote:
When you load this in camera raw, you are applying the uniwb and the histogram you see should be the same as what you saw in the camera. You can then lower the exposure in camera raw and apply a new white balance.
Now there's what I was missing in this equation! I was trying to figure out where the difference was in applying in-camera WB vs out-of-camera WB, and it's because you're dropping the exposure afterwards before applying it.
Thanks, very interesting. Maybe I'll load it as a preset and give it a shot next time I think of it.
Edited on Aug 13, 2008 at 06:43 AM
When you load this in camera raw, you are applying the uniwb and the histogram you see should be the same as what you saw in the camera. You can then lower the exposure in camera raw and apply a new white balance.
Now there's what I was missing in this equation! I was trying to figure out where the difference was in applying in-camera WB vs out-of-camera WB, and it's because you're dropping the exposure afterwards before applying it.
Thanks, very interesting. Maybe I'll load it as a preset and give it a shot next time I think of it.
Edited on Aug 13, 2008 at 06:43 AM
Aug 13, 2008 at 06:42 AM
p.1 #10UniWB
When you are pushing the exposure to the right(of the histogram) use exposure compensation. That way, you can lower the exposure to the point where it will be close to the original scene.
Aug 13, 2008 at 07:21 AM
p.1 #11UniWB
RONIN2 wrote:
i think i have have an understanding of how and why. a big thanks for the links there tomb18. and thanks for some insight Ray. greatly appreciated.
i have the preset saved in my camera, and yes, the images are quite green under daylight conditions. i also tried the preset under incandescent light and got major underexposure in the blue channel. would this be normal and/or expected?
I guess the white balance that the camera would apply without uniwb would push the blues up quite a bit. Did you try to maximize the exposure as well?
i think i have have an understanding of how and why. a big thanks for the links there tomb18. and thanks for some insight Ray. greatly appreciated.
i have the preset saved in my camera, and yes, the images are quite green under daylight conditions. i also tried the preset under incandescent light and got major underexposure in the blue channel. would this be normal and/or expected?
I guess the white balance that the camera would apply without uniwb would push the blues up quite a bit. Did you try to maximize the exposure as well?
Aug 13, 2008 at 07:23 AM
p.1 #12UniWB
i did tomb18. red and green channel were bordering right edge of the histogram. i'll do admit that i haven't tried processing any images using UniWB. i'll have to try a few tonight and see what's up.
Aug 13, 2008 at 07:55 AM