[Radiance-general] Color Bleeding

[Greg Ward]

Hi Marcus,

In brief, I think that 40% reflectance for a wood floor is too high.   
An off-white wall might have a 40% reflectance, but most wood floors  
would be closer to 20%.  If you use macbethcal for your floor capture,  
then it gives you back true reflectance values.  In such cases, I would  
not pass the pattern trhough normpat.

Further comments below:

> From: "Marcus Jacobs" <marcdevon at hotmail.com>
> Date: March 11, 2005 11:34:15 AM PST
>
> For the wood floor image map in this rendering, the image map was not  
> normpat'd and a rgb reflection for the floor (plastic) was set at .4  
> .4 .4. The floor image map brightness is a bit darker than what I  
> would expect:
>
> http://pg.photos.yahoo.com/ph/marcdevon/detail?.dir=/ 
> b3e9&.dnm=d98b.jpg&.src=ph

Here you are multiplying your captured reflectance from the image by  
40%, which makes it 40% of what it should be (most likely).  Too dark,  
as you say.

> For this rendering, the wood floor image image was normpat'd. The red  
> green blue option in colorpict was set to red green blue and a rgb  
> reflection for the floor (plastic) was set at .4 .4 .4. Notice the  
> level of color bleeding in the rendering. Also, the brightness and  
> saturation of the image map is much higher than the pre-normpat'd  
> image map:
>
> http://pg.photos.yahoo.com/ph/marcdevon/detail?.dir=/ 
> b3e9&.dnm=e6b4.jpg&.src=ph

Probably because 40% is too high a reflectance for your floor.

> In this rendering, the wood floor image map was not normpat'd and a  
> rgb reflection for the floor (plastic) was set at 1 1 1. I know not  
> how physically accurate the floor material is reacting but the  
> brightness of the floor material is what I think I would expect:
>
> http://pg.photos.yahoo.com/ph/marcdevon/detail?.dir=/ 
> b3e9&.dnm=adb6.jpg&.src=ph

If you were using macbethcal to create your floor pattern, this is the  
technique I would recommend (using the functions red() green() and  
blue() as the first three string arguments in your colorpict).

> In this rendering, the wood floor image map was normpat'd, the red  
> green blue option in colorpict was set to clip clip clip and a rgb  
> reflection for the floor (plastic) was set at .4 .4 .4:
>
> http://pg.photos.yahoo.com/ph/marcdevon/detail?.dir=/ 
> b3e9&.dnm=3242.jpg&.src=ph

I assume you mean clip_r(), clip_g() and clip_b().  The function clip()  
by itself would always return the red channel, and you would end up  
with a gray-looking floor.

> In this rendering, the wood floor image map was normpat'd, the red  
> green blue option in colorpict was set to grey grey grey and a rgb  
> reflection for the floor (plastic) was set at .4 .4 .4:
>
> http://pg.photos.yahoo.com/ph/marcdevon/detail?.dir=/ 
> b3e9&.dnm=36c5.jpg&.src=ph
>
> In this rendering, the wood floor image map was normpat'd, the red  
> green blue option in colorpict was set to noop noop noop (I think this  
> was recommended in RWR) and a rgb reflection for the floor (plastic)  
> was set at .4 .4 .4. This rendering and the floor is very saturated.
>
> http://pg.photos.yahoo.com/ph/marcdevon/detail?.dir=/ 
> b3e9&.dnm=d1fc.jpg&.src=ph

Again, I don't see how using noop() would give you this image, as  
noop() expects a single argument, and if given three (r,g,b), will  
return the first.

> I guess this is the rundown. Any suggestions?

Again, I suggest using macbethcal to capture your image, and don't run  
normpat unless you have a measured reflectance value to use.

-Greg