WhiteBalance being the greatest factor contributing to the histogram difference is a bit surprising to me. I did some experimentation around this in dcraw [it has an option to set the multipliers to 1 for all three colors (RGB)] and found that the gamma correction had much higher impact than uniWB.
Manish (I think this is your real name), Panopeeper is totally right, the WB (if applied using >=1 multipliers, which is the way cameras do unless I am wrong) severely affects your exposure. WB means to linearly multiply all levels in a channel. Since most sensors have a greater sensibility on the G channel, G levels are usually left unaltered (multiplier=1.0) while R and B channels are scaled up easily by +1EV and even more, blowing highlights in those channels.
For instance, the tungsten preset multipliers for the Canon 350D are: R=1.392498 G=1.000000 B=2.375114
Scaling the B channel by 2.375 means log(2.375)/log(2)=1,25EV overexposure!
Regarding gamma, I am not an expert, but a pure gamma correction
OUT = MAX * ( (IN/MAX)^(1/2.2) )
will not blow anything, it will simply expand the shadows and compress the highlights but without blowing just 1 pixel.
No idea if a pure gamma correction is applied on most cameras, but whatever they do, is surely much less restricting for exposure than WB.
That is why I think your article, being very well written and having a good idea in mind, fails to think gamma is a key factor. Using that curve you will get very dark displays and will not assure to be properly representing the blown areas since WB is still being applied.
In postprocessing, many tricks can be used not to blow those channels when applying the WB during the RAW development, like for example using <=1.0 multipliers. This has the problem of creating magenta casts in the blown areas, but this can be easily fixed by special algorithms that ensure that the blown highlights remain neutral (R=G=B ). For instance DCRAW achieves this through the effective -H 2
An example is coming: I used this option in a severely ETTR shot (see whole article here: ETTR LANDSCAPE
When developed with 1.0 multipliers
, i.e. no WB (DCRAW's -r 1 1 1 1 option), you get this log
When developed with <=1 multipliers
(DCRAW's -H 2 option) the R channel remains unchanged in this case and the G and B channels are underexposed to balance the image and always assuring white highlights:
But cameras don't work this way, they apply >=1 multipliers
(DCRAW's -H 0 option) which would have lead to B and specially R blowing, remaining G unaltered: