Hand-Held High Res: A Practical Guide

Started May 15, 2020 | Discussions thread
Anders W
Anders W Forum Pro • Posts: 22,144
Re: Highlight Protection
5

MEDISN wrote:

Anders, can you share the settings for uniWB on the PEN-F? I was unfamiliar with the concept of uniWB until you and knickerhawk brought it up. I have looked at several tutorials and it's more complicated than I anticipated. Any tips? I assume settings from PEN-F will not apply to EM1's also?

Thank you both for your discussion - I find it very informative. Even if I need to read it several times to understand Also, your old 2015 thread discussing these concepts when the EM5mkII came out was enlightening. I wish I had read it years ago!

OK. So here goes. First a bit of background where I might well be telling you things you are already well aware of. But better a bit too much than a bit too little, I thought, especially since there may be other readers who are interested in what we are talking about.

Everything the camera tells you about exposure, including ordinary metering, histograms and highlight/shadows warnings, is based on the OOC jpegs, not the raw files. Of course, this makes the information less than perfect for those of us who want to shoot the best raws rather than the best OOC jpegs.

In general, universal white balance (UniWB) is a trick to force the camera to provide exposure information better attuned to the needs of raw shooters. What will happen with any more normal WB setting is that the camera will amplify the red and blue channels relative to the two green channels when producing the OOC jpegs. This is so because the level of the red and blue channels in the raw file is ordinarily only about half that of the green channels. Consequently, the green channels will ordinarily clip in the raw file long before the red and blue channels do. In the OOC jpegs, by contrast, all channels tend to reach the clipping point of a whitish area at approximately the same time.

So what we need in order to get reasonably correct information about the actual clipping points in the raw file is a WB settings, known as UniWB, that prevents the camera from amplifying the red and blue channels relative to the green ones when producing the OOC jpeg so that we can see them as they actually are in the raw file. In the special case of Olympus HR shots, UniWB has the additional benefit of preventing unnecessary clipping of the red and blue channels in the pseudo-raw file produced by the camera after first demosaicing and then "remosaicing" the eight individual shots from which the HR raw is created. But that's a special case and not the reason why the idea of UniWB first arose.

Now the camera makers could easily give us a UniWB setting as a fixed WB setting along with all the others (sunshine, shade, cloudy, tungsten etc.) but for some reason they don't. So if we want one, we have to create one ourselves by using one of the custom WB settings available. In the following, I describe how to do that on an Olympus MFT camera. While I haven't personally set a custom WB on more than a few of them, I would guess that all the others work the same way in this particular respect. On Panasonic cameras, the procedure is similar AFAIK. But you will have to refer to the section on WB in the manual for the details in that case.

IIRC, the person who first introduced me to the use of UniWB was a very friendly, helpful, and knowledgeable contributor to this forum known as gollywop, and I'd like to acknowledge his help by linking to the step-by-step instruction he once provided here. I have personally used the procedure he proposed and it works perfectly well as is or with minor modifications. However, I have since found a much simpler way to get it done that works perfectly well on my Pen F and hopefully on other models as well. So here it is:

1. Find an area that you can easily overexpose wildly, so wildly that every pixel still alive on your sensor will clip. A piece of sky in daylight will ordinarily do nicely as such a target. Then put your camera in manual mode and set an f-stop and shutter speed so as to actually accomplish this extreme overexposure.

2. Go to the SCP (Super Control Panel), choose WB, choose one of the custom WB settings (1, 2, 3 or 4), for example, the first of them if you are not already using it for something else, and press the info button.

3, The camera will now ask you to point the camera at a sheet of white paper and press the shutter button. Instead, point your camera at the target you selected in step 1 and press the shutter button. Since you overexposed wildly, the camera will issue a warning that the WB levels are extreme and ask you if you want to continue. Ignore the warning and answer yes to save the custom WB setting.

4. The shot you took in step 3 wasn't recorded but only used to produce the custom WB setting. Now shoot a picture with that custom WB setting. It doesn't matter at all what that picture is or how you shoot it.

5. Take the card out of the camera, go to your computer and open the picture you just shot (raw or jpeg doesn't matter) in a good EXIF viewer that lets you see all the info in the EXIF. The one I personally use is a freeware program called ExifToolGUI. Then look, in the "Olympus" section, for the tag named WB_RBLevels. The values for that tag should be 256 256 256 256, and if they are, you have successfully created a UniWB setting.

Try this, and please let me know if it works out as nicely for you as it did for me.

 Anders W's gear list:Anders W's gear list
Panasonic Lumix DMC-G1 Olympus PEN-F Olympus E-M1 II Panasonic Lumix G Vario 14-45mm F3.5-5.6 ASPH OIS Panasonic Lumix G Vario 7-14mm F4 ASPH +20 more
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