[Openicc] beyond 8-bit precission [was: new version of xcalib]

[Kai-Uwe Behrmann]

Am 08.03.05, 15:46 +1100 schrieb Graeme Gill:

> It depends how you are setting up your 8 bits space. The claim is
> that 8 bits is just enough under the right circumstances. There is
> little or no margin though.

LCDs becomes an high contrast media, where intensity distances 
become bigger and more visible. In case of my monitor (contrast 1:350) I 
can count 244 shades of gray. In the light and dark regions seems no 
information distinguishable to me. 

This means I can make something known to my mind. What is the amount of 
difference sensitivity people can not see by mind but they feel by sense. 
My conclusion is at least what we get to see should be much better than 
what comes visibly in our mind.

If I understood right Longhorn is going beyond todays 8-bit capablities of 
graphics display processing and presenting. This is the right direction.
I would love to see X11 or similiar technology ready to compete.

> > No black/white photographer is convinced by an maximum of 8-bit level of
> > sensitivity.
> 
> But if they are dealing with device space (ie. photographic film),
> or capturing a high dynamic range and expecting to extract a
> "finished" image from it, then of course 8 bits will not
> be enough. 8 bits is just enough for a final image, if it
> is represented in the right colorspace.

My experience with former standard and medium format still photos gave
allways an other feeling. Even if I could not see grain. Today I am very 
happy about the clear shades of gray 8 bit can deliver (no grain) - but in 
the same way I have the feeling, it is not an clear image like an dia or 
an silver photo from medium or large format film.
 
> > This calculation refers to an reflective media, right?
> 
> No, to any image that has been processed and is in a final
> state, so that it has a black point down to L* = 0, and
> a white point of L*=100. Most computer display devices (CRT's,
> LCD's etc.) conform to this assumption. Other technologies
> don't (ie. film projection), where there is the possibility of
> "white than white" highlights.

What is the contrast ratio of film? Are todays LCDs and TV displays 
really that far from film contrast?

> > Todays inkjets have left behind 256 steps - steps in the sense of
> > stepping. Tell me if you like, I can send you an print, which shows
> > clearly each step of 8-bit shades of gray output.
> 
> Once again, I was referring to a carefully constructed space, not
> a device space. The whole point of looking for RAMDAC tables with
> greater than 8 bit entries is to handle the requirements of device
> spaces with sufficient precision to be able to control them.

Sorry but I dont understand. Both, the mentioned print and the LCD setup ,
showed nearby each step in an 8-bit gray ramp. There is no space left to 
move intensities to the one or other end without degrading the used
setup.

> As for inkjets, we were using 8 bit/component systems extremely
> successfully in commercial high quality proofing, and the 8 bit
> limitation was never an issue. The reason was simple, the

Yes, I agree thats fine for proofs. In an printhouse one expects matching 
not sensitivity.  Offsets usually show 6 till 7-bit. Carefully utilized it 
seems enough for this field of appliance.

> system has device calibration, and the 8 bit space was carefully
> constructed to have a close to perceptually uniform transfer
> characteristic. The output of the calibration LUTs (device space
> values) was 12 bits/component.

Thats my experience too.

> > This calculation refers to an reflective media, right?
> > Todays inkjets have left behind 256 steps - steps in the sense of
> > stepping. Tell me if you like, I can send you an print, which shows
> > clearly each step of 8-bit shades of gray output.
> > 
> > Todays artists need more precission!
> 
> For creative use (where images are going to be edited, composed,
> or stored in device spaces), then I fully agree that this is very
> desirable. In practice, there are many 8 bit/component systems
> and storage formats out there, and we have to make the best of them.
> If they are used for final images in an appropriate space, the 8 bit
> limitation need not result in visible artefacts.

Agreed for the current devices. It is fine to use as much as available and 
dont waste resources. 

Anyway,
consequently nearby all media/devices had gone the way from 8-bit to 
more, I expect displaying devices will certainly change. If impulses 
come from cinema, TV , fine arts demand , computer graphics ... ?

regards
Kai-Uwe Behrmann
                                + development for color management 
                                + imaging / panoramas
                                + email: ku.b at gmx.de
                                + http://www.behrmann.name