[argyllcms] Re: Profile input white not mapping to output white

  • From: Iliah Borg <ib@xxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Mon, 26 Nov 2012 20:04:59 -0500

On Nov 26, 2012, at 7:52 PM, Graeme Gill wrote:

> Iliah Borg wrote:
>> Before demosaicking, that is before some form of recombination of raw 
>> channels, we do
>> not have colour information at all. We need to run recombination / 
>> demosaicking to
>> calculate two missing components for each pixel. Raw channel data is some 
>> form of
>> monochrome, recorded as shades of grey so to speak.
> Hmm. You don't need full resolution data to do a white balance

We always have full resolution data from the sensor, but I know what you mean - 
demosaicking is indeed not needed for white balance.

> , and
> yes, you have color information- you have the camera filter
> RGB values from the raw cells.

They are not RGB, camera filters are not RGB, and we do not have the spectrals 
on them too - or we would not need to shoot the targets to create profiles.

> Each cell is a point sample out of it's 2x2.

Yes, and binning is a form of demosaicking.

> ("Demosaicking" is all about trying to invent detail
> that wasn't actually captured

Disagree. It is not invention, it is interpolation.

> , and it generally shows if you
> look at the pixels.

Pretty much the same way as any digitizing, be it image scanning, or audio. 
Worse, 8x loupe shows grain on film (and that is considered to be "print size", 
those 8x - not "display size").

> A downsample by 50% to the actual sampling
> interval always looks a whole lot better in my view.

Images are displayed at about 96ppi, but printed at 300-350, so we have our 
"downsampling" ;)

> It all
> seems to be numbers game, driven by marketing.

In a way, yes. And an unbalanced game on top of that, as limitations come not 
only from the sensor "resolution", but also from other components of a very 
complicated system - all the way from the haze in the scene to the presentation 
of the image.

> If displays were
> rated the same way as cameras, they would magically increase the
> numbers of pixels by 3, without an visual change ...)

That is Foveon :)

Iliah Borg

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