Hi Gary, Unfortunately I rarely touch RS these days. Apart from modelling a few objects for my projects I just don't have time to play. I can't remember what state my GI shader was (using HSV) ir even if I had one!
However, using an HSV colour space throughout the render pipeline might not be too hard. Create a custom HSV channel and in certain shaders do the conversion. Say in Surface Properties for objects, and Light Properties for lights. There's a definite downside to HSV too though. In a partially reflective surface the final Surface Illumination is an average of the object's illumination and the secondary ray's illumination. If you have a white ball (1.0, 1.0, 1.0) reflecting a blue checker (0.0, 0.5, 1.0), the value on the surface would be the mean average. If a particular point on the ball was in 50% illumination, and reflectivity was 50%, the final illumination for that point would be... R : ((1.0*0.5) + (0.0*0.5)) / 2 = (0.5+0.0) / 2 = 0.25 G : ((1.0*0.5) + (0.5*0.5)) / 2 = (0.5+0.25) / 2 = 0.375 B : ((1.0*0.5) + (1.0*0.5)) / 2 = (0.5+0.5) / 2 = 0.5 The end result is a blue reflection. If we were to handle this in HSV space, the white sphere would be (0.0, 0.0, 1.0) and the blue checker would be (0.58, 1.0, 0.5). In the same circumstances as above... H : ((0.0*0.5) + (0.58*0.5)) / 2 = (0.0+0.29) / 2 = 0.145 S : ((0.0*0.5) + (1.0*0.5)) / 2 = (0.0+0.5) / 2 = 0.25 V : ((1.0*0.5) + (0.5*0.5)) / 2 = (0.5+0.25) / 2 = 0.375 This works out as dark mustard yellow! Averaging Hue's doesn't work. The Raytracing process would have to become a lot more complex in it's calculations to work out the correct results. At the moment I'm not sure what calculations would do the job. HSV is tricky to work in. V works okay but H can't be averaged at all and S needs to be changed based on what the other two channels are doing, so can't be dealt with linear interpolation. I guess this is why there's no GPU's that work in HSV! I think it'd be quite a breakthrough in rendering quality if someone could get a working HSV raytracing engine. Every time there's overbright areas in a computer generated image the saturation is always wrong in additive RGB. Maybe a solution is a hybrid that uses S and V in illumination, coupled with RGB processing to derive colours? David Coombes [EMAIL PROTECTED] ... ----- Original Message ----- From: "studio" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Friday, November 11, 2005 2:02 AM Subject: Re: Heads Up ( an old Gi Post Thread Again ) > > > Don't mean to be preaching to you , David , since you obviously > > >see the need and potential , hence your PhotoGrey plugin's use of HSV , > > >but it doesn't seem to be widely accepted or even acknowledged that we > > >live in an HSV world, not the RGB world found in CGI raytracings . > > > Hi Mark : > > Great ! Not sure if David's one plugin will convert you though . Being > able to work in HSV colorspace at every step of the way , might , however , > like is possible in some Paint & Photo programs . > > > Thanks for the HSV plugin David, and sorry for neglecting it all this > > time... > > -Mark H > > Godspeed Markus ! > > Garry Curtis > http://www.niagara.com/~studio > > > > >
