Orchid XP v8 wrote:
>>> OK, that's just absurd. The sofa and the rug are *exactly* the same
>>> colour. How the hell can the machine tell them apart? Additionally, how
>>> on earth can it tell what colour they were originally? That's
>>> impossible...
>>
>> Except it clearly isn't impossible, because it was done.
> 
> Well yeah, OK, I rephrase: It defies explanation.
> 
>> Adjusting the white balance of the photo involves picking out 
>> something that actually is/was white (like the white on the baby's 
>> shirt).  That gives the computer a reference to make the adjustments 
>> from.  When photos age, they tend to age consistently and the colours 
>> adjust with consistency.  The computer basically is doing an "undo" on 
>> the age effect applied by real life.
> 
> But surely no scanner on Earth has sufficient resolution that you can 
> amplify a signal by many orders of magnitude and not be swamped by 
> noise? The photo posted contains almost no blue whatsoever, so you'd 
> have to apply a ridiculous amount of gain to that channel...
> 

The picture is an older, sorta analogue media, it does not fade it's 
colors the same way a bitmap would if bitmaps actually faded. It is so 
predictable, in fact, that baring strange papers and processing, it is 
very easy to correct for. Just treat the picture as if the lighting it 
was shot with was different from normal daylight of around 5500 K.

In effect, the computer doesn't boost the blue channel, it uses a damned 
"nonlinear colourspace transformations".

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