Gear Talk > Camera Talk
UniWB Link -- (and what about Monochrome??)
Andrea B.:
UniWB, a unitary white balance setting for your camera which forces it to use unitary colour multipliers, came up in another topic. As I recently found a very nice summary of a method for setting UniWB, I thought I would make a separate UniWB thread to post the link. I'm hoping some folks will try this UniWB method and report back to this thread.
To review, using UniWB produces a reasonably accurate raw histogram which helps us set exposures properly or which better enables ETTR for highlight preservation in cameras with smaller dynamic range. Everyone is probably somewhat familiar with UniWB's green cast and the need to shoot a white/grey card to restore "correct" white balance when converting fotos made with UniWB.
There are a multitude of UniWB articles out there on the web. So everyone should be able to find scads of additional info about this topic.
Here is the link to an ETTR and UniWB write-up by photographer (and electrical engineer) Jim Kasson in his Last Word blog: Using In-Camera Histograms for ETTR
If you want to cut to the chase, go directly to Section 7: Preparing for Monitor-Based UniWB and Section 8: A One-Step UniWB Procedure
You need Excel for some spreadsheet work unless you want to use a calculator.
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Andrea's Monochrome ETTR Experiment
Using an in-camera Monochrome setting seems to be useful for ETTR. Monochrome's R, G, B and L histograms all look the same, of course. What I am currently trying to figure out is how accurate the histogram is when viewed in Monochrome and whether there are any supporting settings which might be useful. For Nikon cameras, this would be such settings as Picture Control's Brightness or Contrast and in-camera ADL. Other cams no doubt have similar settings.
I tripped onto using Monochrome to better deal with the difficult exposures encountered in my UV work in which all colour is false and blown channels abound. My thinking on using Monochrome ETTR is that if we get the Light right, the Colour will follow (eventually). ;D
Should that be a motto??? Get the Light Right and the Colour Will Follow. :D 8)
I'm certainly not claiming to be the first to ever think this. Eons & ages ago a very helpful photographer once showed me how to convert a colour foto by first dealing with the light in a monochrome version before tackling the colour. I don't think I have ever seen any write-ups of this. But then there is a huge web out there and little time for me to search out links.
To better test the feasibility of Monochrome ETTR, I need to shoot some comparisons with that and UniWB. So I'll try to do that and report back to this thread too.
Frank Fremerey:
--- Quote ---Eons & ages ago a very helpful photographer once showed me how to convert a colour foto by first dealing with the light in a monochrome version before tackling the colour. I don't think I have ever seen any write-ups of this. But then there is a huge web out there and little time for me to search out links.
--- End quote ---
Dan Margulis and his Photoshop Professional book series explain how to treat exposure and contrast apart
from color. Margulis is a very demanding read ... a physicists approach to color contrast and exposure and a
new way to see color for editing in 10 channels ... very enlighting and helpful ...the chapter about how to use the
green channel to sharpen hair and eyes independently of the skin .. wow.
http://www.moderncolorworkflow.com/dan-margulis
Shane:
--- Quote ---What I am currently trying to figure out is how accurate the histogram is when viewed in Monochrome and whether there are any supporting settings which might be useful.
--- End quote ---
In-camera conversion to monochrome uses a typical luminance formula
RGB Luminance value = 0.3R + 0.59G + 0.11B
Note that this is heavily weighted towards the G channel.
Here's the problem with a luminance histogram.
It doesn't indicate when one or two channels may be saturated for strong colours e.g. red or blue flowers.
Example: If the RAW B channel (and/or R channel) data is at saturation point and the other channels are below saturation then the luminance histogram will under report a saturated channel.
Saturated Red & Blue Pixel: Y = R255x0.30 + G250x0.59 + B255x0.11 = 252
Using UWB the histogram will "correctly" report the B channel is saturated and that reducing the exposure might be in order.
Andrea B.:
Yes, I'm aware of that, of course. But, one (or two) oversaturated channel(s) is easy to deal with. I don't usually really care if I've blown one (or two) channel. Well, blown, but not too far, that is. There is always a point of no return.
Recently for example, I reduced blown red in a NEF by using an NX2 color point and decreasing the contrast in the blown red by a mere -2 points without affecting other colours/contrasts. [Other converters have other methods for dealing with this. Just wanted to present one example.]
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Shane, do you know of Kasson's UniWB tutorial which I linked above? I'm just setting up now to try it out. Last time I attempted to produce a UniWB, I got into some kind of crazy non-convergent loop. So I am wanting to try again with a new tutorial.
Shane:
--- Quote ---There is always a point of no return.
--- End quote ---
And that is when the original RAW data is saturated. Either RAW data is "blown" or it isn't, there is no in between. Once it is saturated then any "recovery" is an apparent recovery and still results in loss of detail. If you can recover a "blown" channel then it was an apparent recovery or, it wasn't really blown to begin with but just a result of WB, colour space application etc.
If the RAW data is truly saturated and you recover it then, you will lose any fine detail that may have been present in the subject. This of course may be acceptable in some cases.
I have used Kasson's method for a while now for creating UWB for a D800, D800IR830 and my D810. It works really well and is pretty quick providing you set it up by carefully following the directions.
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