[Radiance-general] Re: measuring color

[Greg Ward]

Hi Alexa,

>> ...
>> However, I think others will agree that pcond can be useful, and is 
>> an improvement over the standard "linear with clamping" method for 
>> image display.
>
> I don't doubt that it is better for image display and I think the idea 
> with these kind of mappings is to go down the route of 'perception' 
> rather than 'physics', one reason being the current limitations of 
> CRT's e.g.
>
> My concern is physical accuracy. I want to display an image on a 
> screen (eventually) and people should not be able to tell it apart 
> from the real world scene. Of course, I can only simulate colours and 
> luminances that my daft 8-bit monitor can actually render.

There are surround issues to consider as well, especially since the 
monitor only covers a small portion of your view.  Pcond attempts to 
adapt the original scene levels to the current viewing environment -- 
something not even an HDR display can do.  You need something like the 
wide-field HDR viewer I built to test out tone operators for that.

> Talking about the limitations of CRT's. Has somebody seen 
> DLP-technology displays in action and maybe even made some colour 
> measurements? Apparently, the colour resolution can be cranked up to 
> 15 bits per channel and the luminance range is also much bigger. I 
> only wonder, if the 15-bit resolution per channel is actually really 
> an improvement in terms of colour resolution for a given luminance 
> level (in comparison to a traditional 8 bit resolution)  or is 
> basically necessary to cover the increased luminance range?

If the 15 bits is in a linear range, and a DLP is a linear device, then 
you don't actually gain much in terms of dynamic range over an 
8-bit/primary encoding using a standard 2.2 gamma.  Beware of 
manufacturer's claims regarding contrast ratios and bit depths.  There 
are no standards, and the marketing people have a field day with these 
specs.  Bottom line:  don't trust it unless you've measured it 
yourself.

> Is that the same technology used in last year's emerging technology 
> SIGGRAPH session:
> Seetzen, H., Stuerzlinger, W., Vorozcovs, A., Wilson, H.R., Ashdown, 
> I.,
> Ward, W. and Whitehead, L., 2003, High Dynamic Range Display System. 
> SIGGRAPH 2003, Emerging Technologies Program.
> http://www.siggraph.org/s2003/conference/etech/hdr.html

We actually have a full-blown paper in this year's Siggraph, which is 
now online as well at Wolfgang Heidrich's website if you're interested:

	http://www.cs.ubc.ca/~heidrich/Papers/index.html#siggraph

This is a very cool device, but is only available in limited quantities 
as a prototype to select companies and individuals.  Sunnybrook 
Technologies (http://www.sunnybrooktech.com/ Vancouver, BC) hopes to be 
manufacturing the real deal by next year.  As I said, even an HDR 
monitor doesn't deal with surround issues, so it's really quite 
difficult to reproduce the visual appearance of the real world in all 
it's glory.

-Greg